Transition from normal to cancerous cell by precancerous niche (PCN) induced chronic cell-matrix stress

The attempt to restore homeostasis, once disrupted, such that complex signaling, crosstalk between ubiquitous proteins, and a diverse range of pathways gone awry is near impossible, especially in the presence of an ongoing pathogenic stimuli with incessant inflammation. This persistent inflammation, when unresolved, induces fibrosis with consequent remodeling of the extracellular matrix (ECM) which leads to the formation of the precancerous niche (PCN), the tipping point in the transition of normal to cancerous cells. Thus, the sustained disruption of homeostasis when confronted with limited adaptation capabilities either of cells or of the surrounding matrix and faced with chronic stress in the tissue microenvironment results in an escape strategy which, if unsuccessful, causes cells, tissue, or the organism to become unable to recover over the long term. All conditions necessary for cell–cell transition such as deregulation of cell–cell complexes, decrease in the stability of adherens junctions, together with the apical-basal polarity, and the loss of the cytoskeletal architecture occurs as a cascade of events inducing inappropriate and diverse signaling pathways and crosstalk. In biology, the transition of one cell type to another and the transition from one cell function to another is incompletely understood mechanistically, but within the context of embryogenesis and morphogenesis is acknowledged as a physiologically routine event. The constant stress that can result in the development of the PCN leads to a chronic stress escape strategy (CSES) which, if unsuccessful, eventually triggers a normal cell- to-cancer cell- transition (NCCCT).

However, cells can switch between different types of polarity and cell transition needs much more to go awry such as "signaling networks, transcription factors, membrane-trafficking pathways" [21].
"The transition from one cell function to another, as well as the transition of one cell type to another seems to be a routine event rather than a rare one" [22]. The cell-cell communication as well as of the ECM influences the polarity, and perhaps most importantly, malignant transformation of mammary epithelial cells by alterations of the ECM including the complex interplay of various signaling pathways such as the metalloproteinases (MMPs) and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs) ( [23] reviewed in [24]).
Tissue inhibitor of metalloproteinases-1 (TIMP-1) can induce hepatocyte growth factor (HGF/scatter factor) accompanied by increased metastasis and triggering of its corresponding genes in colorectal cancer metastasis [25]. In this regard, gelatinases are of for cellular homeostasis as well as for metastasis [26]. For example, Helicobacter pylori (H. pylori) infected gastric mucosa increases interleukin 21 (IL-21) and promotes gelatinases, matrix metalloproteinase 2 (MMP-2), and matrix metalloproteinase 9 (MMP-9) synthesis through nuclear factor kappa-lightchain-enhancer of activated B cells (NF-jB) [27]. The disruption in homeostasis by signaling and crosstalk of ubiquitous proteins [28] in the presence of ongoing pathogenic stimuli induces unresolved chronic inflammation which has been reviewed elsewhere in this Special Issue [29,30].
Cell transition during carcinogenesis is difficult to break down to just a few signaling pathways, receptors, or cell types. Some specific pathways might be differently affected and/or dependent on other influences, e.g., some signaling will occur during embryology (normal physiology) or influenced by ongoing pathogenic stimulus while different changes in homeostasis may provoke different effects. These may be the reasons why cell transition in general is restricted and why it is necessary to understand in all its complexity. Here we provide information on cell transition with regard to embryology, pathogenic stimulus, the role of the retinoblastoma (RB) protein family and apoptosis, chronic inflammation, and the role of the retinoblastoma coiled coil protein 1 (RB1CC1), fibrosis and its remodeling, all working towards the precancerous niche (PCN). In addition, various signaling pathways such as pituitary tumor transforming gene 1 (PTTG1), catenin beta-1 (b-catenin), sex-determining region Y (Sry)-related high-mobility-group Box (SOX), microRNAs, histone acetyltransferase p300 (p300, adenovirus early region 1A (E1A)-associated protein p300), specificity protein 1 (transcription factor) (SP1), activator protein 1 (AP-1), aryl hydrocarbon receptor (AHR), long interspersed nuclear element-1 (LINE1) and chronic cell matrix stress including STE20-like serine/ threonine-protein kinase (SLK) signaling provide insights that are helpful to review so as to unmask the process of cell transition during carcinogenesis.

Embryology
Cell transition is absolutely necessary for embryogenesis and morphogenesis but incompletely understood. However, the "transition from one cell function to another, as well as the transition of one cell type to another seems to be a routine event rather than a rare one" [22,31]. For example, some 50 years ago it was shown that free-floating "peritoneal macrophages" replaced destroyed mesothelial cells via transformation of its original macrophage role to that of mesothelial cells [32,33]. Chronic lung injury, under some circumstances, can result in transition to cancer [34]. An EMT in embryogenesis/morphogenesis acts in a direction opposite to that of a mesenchymal-epithelial transition (MET) [35]. EMT can induce non-cancer stem cells to become cancer stem cells [36,37].
HDAC8 is involved in tissue development [39] and in various diseases. HDAC8 is increased in lung fibrosis and anti-HDAC8 therapy decreases type-1 collagen and fibronectin while increasing the anti-fibrotic peroxisome proliferator-activated receptor gamma (PPAR-c) [41] and is associated with poor survival in neuroblastoma [42]. HDAC8 knockdown decreases cell proliferation in lung, colon, and cervical cancer cell lines [43]. Furthermore, AHR and HDAC8 are enhanced in liver cancer cell lines and tissues, and HDAC8 inhibition upregulates the cyclin D-retinoblastoma protein (RB, RB1) in vitro and in vivo through AHR [44].

Pathogenic stimulus
Normal to metaplastic gastric epithelial cell proliferation is coordinated by hyaluronic acid cluster-ofdifferentiation (CD) cell surface glycoprotein (CD44) receptor in H. pylori-or tamoxifen-induced atrophy of acidsecreting parietal cells (PCs) [45]. Cell damage induces extracellular signal-regulated kinases (ERK, mitogenactivated protein kinase [MAPK]) signaling resulting in an increase in CD44 which then binds to signal transducer and activator of transcription 3 (STAT3) and reduces the proliferation response. CD44 is encoded by one gene on chromosome 11 [46] and consists of a constant part encoded by exon 1-5 and 16-20 which are included in all isoforms; N-and O-glycosylation increases CD44 heterogeneity and CD44 is synonymous with a large transmembranous proteoglycan surface molecule family.
In vitro experiments of EBV associated keratitis show that transforming growth factor beta 1 (TGF-b1) promotes spleen tyrosine kinase (Syk) and proto-oncogene tyrosineprotein kinase (Src) signaling after phosphatidylinositide 3-kinase (PI3K)/protein kinase B (Akt) and ERK activation resulting in cell transition in human corneal epithelial cells (HCECs) [54] which may be seen as an ignition point for cell-to-cell transition.
The association between pre-B-cell leukemia transcription factor homeobox (PBX) with PBX1-4 in human and H. pylori is of interest: H. pylori increases the transcriptional factor PBX1 followed by downregulation of connexin 32 (Cx32) [55]. Decreased Cx32 is correlated with "the degree of tumor cell differentiation with unrestricted growth control" ([56] reviewed in [55]).
Three amino acid extension loop proteins (TALE) play a role in cell differentiation and embryogenesis and include the trimeric DNA-binding complexes of PBX, the regulating protein-1-2 of the Homebox gene (Hox) with PBX/ Knotted 1 Homeobox 1 (PKNOX1), PKNOX1-2, PBXregulating protein-1-2 (PREP1-2), the DNA binding cofactors MEINOX (a contraction of MEIS and KNOX) for PBX and Hox with myeloid ecotropic viral integration site1-3 (homebox protein Meis1-3) [57-59]. However, these transcription factors interact independently in addition to being integrated into multiple pathways. For example, Meis1 acts as a purported oncogene, promoting cell proliferation and resistance to apoptosis, and was reported to be highly expressed in ovarian cancer [60].
Amplification . PREP1, Meis1, and PBX1 single nucleotides can be found in cancers and, the absence of PREP1, induces DNA damage. The fact that TALE gene amplifications are not frequent in that only 5/287 gastric cancer patients showed a deletion with one patient showing a truncating mutation in PREB1 also suggests that Meis1 alterations are also not very common and reported in 14/178 lung squamous cell carcinomas. This may be due to the fact that the majority of mutations occur after the onset of carcinogenesis as previously proposed [22].
It appears that both PREP1 and Meis1 compete in terms of their suppressive and oncogenic effects in carcinogenesis [59]. This might be relevant since different cancer phenotypes might be dependent on the kind and grade of disruption of their homeostasis at different points in the pathways. PREP1 has been associated with induction of cell transition and cancer spread through the TGF-b/ SMAD3 pathway in non-small cell lung carcinoma (NSCLC) [71]. As Meis1 was reported to induce G1/2 arrests and non-apoptotic cell death through decreased levels of Survivin and B-cell lymphoma 2 (Bcl-2) [66], its non-oncogene effect might be a matter of concentration which, in turn, argues in favor of the disruption-of-homeostasis concept in carcinogenesis. Meis1 associated cell growth promotion is directly linked to RB1 cell-cycle signaling [72].

Retinoblastoma (RB) protein family
The RB protein family contains the tumor suppressor RB1, the retinoblastoma-like protein 1 (p107, RBL1), and the retinoblastoma-like protein 2 (p130, RBL2) [73]. RB1 can be inactivated by phosphorylation resulting in cell cycle progression. It is important to note that Rb1 has independent cellular functions depending on its being un-phosphorylated, mono-phosphorylated, or hyperphosphorylated [74][75][76][77]. This condition is also independent from Myc amplification [78]. RB1 binds and inactivates the transcription factors E2 promoter-binding-protein-dimerization partner (E2F-DP) dimers and thus prevents cell cycle progression [79]. This explains why the majority of human OSCC do not express RB1 measured by immunohistochemistry, and that those which express RB1 (some 20%) reveal the inactive (phosphorylated) form [80].
EBV infection is inversely correlated with the expression of RB1 in Reed-Sternberg cells in classic Hodgkin lymphoma [81] and RB2/p130 was inversely correlated with vascular endothelial growth factor (VEGF) expression and tumor aggressiveness in cyclin-dependent kinase inhibitor 1B (p27 KIP1 )-negative hepatocellular carcinoma (HCC) patients and both were independent of tumor staging [82]. An inverse correlation of retinoblastoma protein was observed in head and neck squamous cell carcinoma [83].
Otherwise, it should be noted that the retinoblastoma protein 2 (RB2)/p130 immunohistochemistry (IHC) false positive rate can be as high as 22% [84] and that RB1 degradation by the human papillomavirus (HPV) E7 of the HPV type 16 might overcome the cellular response in high-risk HPV [85]. The necessity of zinc which has been reviewed in this Special Issue in various signaling pathways is also of importance as the E7 carboxyl terminus consists of a zinc-binding motif [86]. HPV E7 proteins even stimulate proliferation independently of their ability to interact with RB [87]. HPV E6/7 proteins can induce a decrease of the human suppressor protein 53 (p53) but also interact by p53 independent pathways inducing apoptosis [88].

Apoptosis
The self-induced death of cells called apoptosis involves "typical morphological features, such as shrinkage of the cell, fragmentation into membrane-bound apoptotic bodies and rapid phagocytosis by neighbouring cells" and chromatin condensation, membrane blebbing or ultrastructural modification of cytoplasmic organelles along with activation or suppression of specific signaling and crosstalk pathways [89][90][91][92]. At first, it was thought that apoptosis occurs spontaneously in cancers and was largely associated with anti-cancer treatment [93] but there is a difference in apoptosis in existing cancer compared to the development of a cancer cell (carcinogenesis) as here it is not just about how the double-strand cleavage of nuclear DNA occurs.
We now recognize the importance of the interruption of signaling pathways and decreased apoptosis, which typically is necessary for maintaining and regulating homeostasis of chronic cell stress matrix cells. Furthermore, decreased apoptosis is important during carcinogenesis [94]. Most important in the apoptotic process are caspases [95] but also caspase-independent pathways [96,97] and the interplay between various extrinsic receptors, such as the death type 1 TNF receptor (TNFR1), TNF receptor-associated death domain (TRADD), Fas-associated death domain (FADD), as well as cysteine proteases like caspase 8, and intrinsic pro-apoptotic proteins and the homeostasis between pro-apoptotic proteins Bax, Bak, Bad, Bcl-Xs, Bid, Bik, BIM and Hrk, and anti-apoptotic proteins Bcl-2, Bcl-XL, Bcl-W, Bfl-1 and Mcl-1 ( [95,98,99] reviewed in [94]).

Chronic inflammation
The extensive review of chronic inflammation triggered by pathogenic biological and/or chemical stimulus is presented elsewhere in this Special Issue [29]. Chronic pancreatitis with chronic inflammation is a well-known precancerous condition [100,101] and the important role of TGF-b1 had been discussed [29].
TGF-b1 induces lysyl oxidase (LOX) expression, secretion, and proteolytic processing in normal as well as in mammary epithelial cells and LOX downregulates the E-cadherin suppressive effect [102] while upregulating vimentin [103,104]. Both the upregulation of vimentin and the downregulation of E-Cadherin were observed at the mRNA level [104].
Chronic inflammation in mice and human colitis causes inactivation of retinoblastoma protein by hyperphosphorylation with consequent increase of cell proliferation [105]. Furthermore, dietaryinduced obesity in rats results in the downregulation of RB1 [106]. HPV proteins E6 ad E7 bind and inactivate p53 and RB1 [107] and HPV decreases E-cadherin and downregulates RB1, and interestingly, EBV seems to act as a co-factor [108]. The coinfection of H. pylori and EBV was reported to increase chronic inflammation being of importance for the severity of gastritis in young patients as well as for the development of gastric carcinogenesis [109,110].
RB1CC1 is regulator of cell differentiation and proliferation and modulates TGF-b signaling through the RINGtype E3 ubiquitin ligase, Arkadia [111].

Retinoblastoma coiled coil protein 1 (RB1CC1)
RB1CC1 is closely related to RB1 expression in various epithelial and mesenchymal cancers [112,113]. RB1CC1 is correlated with RB1, and RB1CC1 seems to be a RB1 regulator [114]. Furthermore, RB1CC1expression induces pancreatic stellate cells (PSCs) and correlates with pancreatic fibrogenesis [115]. RB1CC1 knockdown decreases alpha smooth muscle actin (a-SMAD), collagen expression and autophagy with consequent inhibition of pancreatic duct ligation-induced pancreatic fibrosis while RB1CC1triggered autophagy induces PSC activation and pancreatic fibrogenesis in chronic pancreatitis. Comparing human OSCC progression with a mouse model revealed an increase of TGF-b1, N-cadherin, p53 and RB1CC1 with a decrease of E-cadherin from normal oral mucosa to OSCC while it was "increased in lymph node metastases in both human and mouse samples" [116]. It was also shown that "altered ductal carcinoma in situ (DCIS)-associated myoepithelial cells promote the invasive progression of DCIS into invasive ductal carcinoma (IDC) via TGF-b signaling activation" [117]. Only some 8% of 169 investigated DCIS cases showed an aberrant molecular alteration.

Fibrosis and its remodeling resulting into the precancerous niche (PCN)
The role of remodeled fibrosis in creating the PCN has been reviewed separately in this Special Issue [118]. The decrease of E-Cadherin contemporaneously with ECM degradation appears to be relevant for transition of a normal cell to a cancer cell. The subunit enhancer of the zeste homolog 2 (EZH2) of Polycomb Repressive Complex 2 (PRC2), a complex with histone methyltransferase activity, results in increased expressions of Snail, Slug and vimentin with decreased E-Cadherin expression, and is associated with increased fibrosis together with ECM destruction, plasminogen activation, downregulating of adherens junctions, and increased cell transition [119]. Inhibiting EZH2 with 3-Deazaneplanocin A (DZNep) results in the inhibition of growth and reduced fibrosis in endometriosis along with an attenuated EMT.
LOX phosphorylates p130(Cas) (breast cancer antiestrogen resistance protein 1, BCAR1) resulting in the formation of p130(Cas)/adaptor protein Crk/dedicator of cytokinesis (DOCK180) signaling complex while increasing Rac and cdk42 activity regulating actin filament formation with an increase of the cytoskeleton protein, lamellipodium [123]. Lamellipodium is a myosin-independent mechanosensor [130] that drives cell migration in many normal and pathological conditions [131] and is promoted by Rac [132].
The FAK/p130(Cas)/Rac/lamellipodin complex transduces signaling information from matrix stiffnes into mechanosensitive cell cycling and "converts external information encoded by ECM stiffness into stable intracellular stiffness and mechanosensitive cell cycling" and, therefore, has an effect on cell migration as well as on the regulation of the cell cycle [133].
Snail promotes cell transition in a SMAD3/STAT3dependent manner in chronic pancreatitis associated with diabetes [134]. LOXL2 drives EMT through the inositolrequiring enzyme 1 (IRE1)/X-box binding protein 1 (XBP1) signaling pathway inducing Snail, Slug, ZEB2, TCF 3 which are all direct transcriptional targets of XBP1 [135]. Snail and Slug downregulate E-Cadherin. Loss of Ecadherin expression was associated with cell transition in esophageal spindle cell carcinoma which may trigger Snail neoexpression while N-cadherin appears to be of lesser importance in the pathogenesis of this tumor type [136].
Bleomycin induces collagen I synthesis in pleural mesothelial cells with increases of vimentin and a-SMAD and decreases in E-Cadherin by TGF-b1/Smad2/3 signaling with associated cell transition [139]. Activating the complex consisting of TGF-b1, lectin-like oxidized low density lipoprotein receptor-1, and krüppel-like factor 6 (KLF6), in lung tissues of diabetic patients results in increased cell transition along with pulmonary fibrosis [140]. A role for N-acetyl glucosaminyl transferase during cell transition induced by TGF-b1 signaling was reported [141]. More recently, it has been shown that this occurs via downregulation of non-muscle myosin II-A through c-Jun N-terminal kinase (JNK)/P38 mitogen-activated protein kinase (P38)/ PI3K pathway in lung cancer [142].
Stiff, but not soft, fibronectin substrates induce cell transition dependent on a contractile phenotype with TGF-b activation [143]. Matrix stiffness promotes Twist1 release from the cytoplasmic binding partner Ras GTPase-activating protein-binding protein 2 (G3BP2) with nuclear Twist1 translocation. Twist1/G3BP2 signaling responds to biomechanical signaling from the microenvironment with invasion and tumor spread and drives cell transition and metastasis [144]. The pro-inflammatory mediator, interleukin 6 (IL-6), enhances Twist1 in fibroblasts and STAT3 phosphorylation with consequent cancer-associated fribroblast transdifferentiation [145,146]. Furthermore, Twist1 upregulates the nuclear transcriptor protein paired related homeobox 1 (Prrx1) which increases the glycoprotein Tenascin-C (TNC) with consequent positive feedback loop (PFL) by enhancing Twist1 again. The continous Twist1-Prrx1-TNC PFL interaction results in fibrosis in vivo in fibrotic disease and cancer-assosicated stroma and this positive feedback loop can become irreversibly activated [146,147].

Pituitary tumor transforming gene1 (PTTG1)
The highly aggressive castration-resistant prostate cancers (CRPC) grow outside the prostate into adjacent tissues or metastasize (mCRPC) early with a 5-year survival rate of between 15 and 30% [148,149]. PTTG1 is upregulated in cancers such as colorectal cancer [150] and CRPC and regulated by IL-6/STAT3 promoting cell transition [151].
In another endocrine tumor, breast cancer, PTTG1 was increased in recurred estrogen receptor positive (ERpositive) breast cancers ( [152] reviewed in [151]). Ionization radiation can induce senescence in PTTG1-depleted cancer cells [153,154] and can suppress cancer cell proliferation by induction of cellular senescence; inhibiting autophagy can result in a "switch from radiation-induced senescence to apoptosis" [155].
Dicer, an endoribonuclease, discovered in 2001 [166], is downregulated by b-catenin and reported as a marker for cancer aggressiveness which appears to facilitate the spread of ovarian cancer [167].
The canonical Wnt/b-catenin signaling is co-activated by Smad2 through the histone acetyltransferase activity of p300 [168].
Sry-related high-mobility-group Box (SOX) imbalance ( Fig. 1) SOX factors are regulators of transcription and multiple SOX factors have been reported in mammals in nearly every tissue [169]. The functions of SOX genes, including a phylogenetic study of the SOX family and its role in evolution, have been extensively reviewed [170]. SOX4 is a transcriptional factor expressed in B-and T-lymphocytes involved in embryonic development, but its function in apoptosis and cell fate is not completely understood. SOX4 is necessary during organogenesis of the heart, pancreas, and brain and SOX4 regulates EMT by controlling Ezh2 expression and epigenetic reprogramming [171]. Elevated SOX4 levels were associated with poor outcomes in colon cancer [172], gastric cancer [173], lung cancer [174] and osteosarcoma [175].
miR204 was shown to directly target SOX4 in human renal cancer cells suggesting that it could be a marker for the early detection of metastases [176]. Downregulation of SOX1 was associated with improved survival in HCC suggesting that the imbalance of SOX plays a role in the development of cancer [177]. microRNAs ( Fig. 1) microRNAs (miRNAs) are small non-coding RNA regulating genes in plants, animals and in some viruses and many miRNAs have been observed in association with cancer [178]. miR204 expression was reported as being lower in H. pylori-positive gastric mucosal tissue [179]. miR204 directly targets SOX4 and suppress both proliferation and metastasis of gastric cancer AGS cells. miR-204 is not associated with lymph node metastasis or early tumor stages whereas SOX4 was shown to be associated with lymph node metastasis and advanced tumor stages [173,180]. miR204 is downregulated in severe H. pylori associated gastritis as well as H. pylori-positive gastric cancer cells, and in a transfection model with hsa-miR-204 mimic/inhibitor oligonucleotides in human gastric cancer cell lines, SGC-7901 and MKN-45, cells suppresses in vitro migration/invasion and proliferation of gastric cancer cells [180]. This may explain why an inverse correlation of miRNA204 with SOX4 was reported viz., higher SOX4 is associated with lower miRNA204 and vice versa and miRNA204 directly targets SOX4.
miR-503 directly targets Cyclin D1 and functions as a tumor suppressor as it reduces Cyclin D1 expression [181] which might be of therapeutic value as high Cyclin D1 levels were associated with decreased survival and higher recurrence rates in esophageal squamous cell carcinoma (ESCC) [182]. miR21 is a regulator of mesenchymal phenotype transition which is triggered by TGF-b [183]. Early fibrosis in chronic obstructive pulmonary disease (COPD) patients shows increased miR21 levels [184]. Increased miR21 levels also result in a decrease of the TGF-b1 regulator Smad7 and this deregulation enhances aSMA-mRNA, protein levels, and collagen accumulation [185].
Programmed cell death protein 4 (Pdcd4) interferes with JNK-mediated phosphorylation of c-Jun and recruitment of the coactivator p300 by c-Jun [186]. miR21 downstream of the tumor suppressor, Pdcd4, results in increased cancer invasion and spread [187,188]. The disruption of miR21 homeostasis can be seen as miR21 inhibits Smad7 resulting in the withdrawal of the otherwise available negative feedback regulation of TGF-b1 [189] miR21 represses the tumor suppressor phosphatase and tensin homolog (PTEN) [190] and inhibits protein BTG2 (Btg2), protein sprouty homolog 1 (SPRY1), and protein sprouty homolog 1 (SPRY2) that usually negatively regulate the RAS/ MAPK/Erk pathway [191] such that in the end the RAS/MAPK/Erk signaling is enhanced. However, the global dysregulation of the microRNA network is more complex than discussed here and much remains to be elucidated in vivo [182,192]. p300 ( Fig. 1) The enzyme, p300 (synonym: histone acetyltransferase p300, E1A-associated protein p300, EP300), discovered in 1994 [193], is a transcription promoter catalyzing histone acetylation via its histone acetyltransferase activity [194]. p300 and related cyclic adenosine monophosphate (cAMP)-response element-binding-protein was suggested to be "molecular interpreters" that can parse and/or conjugate the regulatory "words," "phrases," and "sentences" of the genome" [195]. p300 is involved in TGF-b/Smad mediated alpha 2(I) collagen expression [196] as well as in glomerulonephritis in a pSmad2/3 dependent manner [197]. p300 and had been reported in cancers of the breast [198], lung [199], colon [200], prostate [201] and in leukemia ( [202] reviewed in [194]). However, its role depends on which cell lines and/or tissue and/or medium is being examined, the method by which p300 is measured, and even if Figure 1. Disruption of signaling homeostasis induced crosstalk in the carcinogenesis paradigm "Epistemology of the origin of cancer". Simplified scheme of the Disruption of signaling homeostasis induced crosstalk in the carcinogenesis paradigm "Epistemology of the origin of cancer" consisting of a six-step sequence: (1) a pathogenic stimulus followed by (2) chronic inflammation from which develops (3) fibrosis with associated remodeling of the cellular microenvironment; and from these changes a (4) precancerous niche (PCN), a product of fibrosis, with remodeling by persistent inflammation, develops which triggers the deployment of (5) a chronic stress escape strategy and when this fails resolve it by (6)   Wnt/b-catenin activity is involved. Huh et al. found that increased nuclear p300 was associated with improved disease-free survival rates in colorectal cancer patients [203]. As pointed out correctly by Bordonaro and Lazaravo, "we would expect that cell lines derived from metastases would exhibit a greater degree of CBP-Wnt activity and less p300-Wnt activity compared to matched primary tumor samples from the same patient" [204]. miR21 downregulates the transformation suppressor Pdcd4 [187], and Pdcd4 usually inhibits the recruitment of the coactivator, p300, by c-Jun [186], suggesting that increased miR21 together with Pdcd4 suppression may be associated with increased p300.
Specificity protein 1 (SP1) (Fig. 1) SP1 is a member of the SP transcription factor family containing "C2H2-type zinc fingers and resembles the larger family of 'Krüppel-like factors' ( [205] reviewed in [206]) [ [Kadonaga Cell 1987]. Zinc is necessary for nuclear translocation as well as for specific high-affinity binding ( [208,209] reviewed in [206]). SP1 can have dual roles. For example, SP1 binding at the proximal and distal enhancer site activates transcription of the human topoisomerase IIa promoter "while competition between Sp1 and Sp3 for binding at either the distal enhancer or at both binding regions results in Sp3dependent repression" ( [210] reviewed in [206]).
The important interplay between SP1 and chronic inflammation as a sequence in carcinogenesis is supported by the following examples: cytokine-driven PI3K/Akt/ Sp1 together with hydrogen sulphide (H 2 S) impairs inflammation in an in vitro pancreatitis model [221]. SP1 binds to the promoter of the T-cell-specific T-box transcription factor (TBET) and enhances it in a dose-dependent manner, TBET and interferon gamma (IFc), in secretion in natural killer (NK) cells and T cells [222]; non-steroidal antiinflammatory drugs (NSAIDs) inhibited ERK activity with consequent lower SP1 phosphorylation and lower activation of MMP-2 [223].
The Food and Drug Administration (FDA)-approved antihypertensive, Losartan, is an angiotensin II receptor type 1 inhibitor. Losartan (Los) suppresses fibrosis in cardiac muscle in mice [227], as well as inflammation and beta amyloid in rats [228]. Los decreases aszites in ovarian cancer [229], and experimental hepatocarcinogenesis and HCC development together with acyclic retinoid (ACR) [230] as well as tumor progression from DCIS to invasive cancer in breast cancer cell lines [231]. The Los effect appears to be associated through the suppression of THBS1 [232][233][234] with consecutive decrease of TGF-b1, via decreases in the MAPK and NF-jB pathways in B and T cells [235] and induced antifibrotic miRNAs [229]. Furthermore, Los suppressed "cell proliferation in a dose-dependent manner, induced apoptosis, decreased YAP (Ser127), and downregulated the YAP target genes CTGF, CYR61, ANKRD1, and MFAP5" [236]. Los inhibit "intracellular angiotensin-II production and AGTR2 nuclear localization to enhance the antitumoral effect of 5-FU in an OSCC tumor model" [237].
The intratumoral distribution and antitumor efficacy of nanoparticles are increased by Los [238]. Los increases paclitaxel efficacy and delivery for ovarian cancer [229], doubled progression free-survival in pancreatic cancer patients [239], reduced cancer-specific mortality in a population-based cohort study gastro-esophageal cancer between 1998 and 2012 from English cancer registries [240], and increased, retrospectively, overall survival by 30 months compared to standard therapy in ovarian cancer patients [229].
Treating pancreatic cancer xenografts with mithramycin (M) and tolfenamic acid (TA) resulted in Sp1 protein degradation and the combined treatment revealed fewer side effects compared to MIT or TA treatment alone [241]. Combining MIT with betulinic acid (BA) in a xenograft mouse pancreatic cancer model resulted in SP1 and VEGF promotion, transcription, and downregulation. This therapeutic regime resulted in fewer side effects compared to gemcitabine [242]. SP1 can function as TGF-b mediated increased expression [243] and it has been reported to play a role in cell transition in gastric carcinoma cells which can be inhibited via miRNA-223 [244]. Dehydroandrographolide is an extract from the herbal medicine, Andrographis paniculata (Burm f), which upregulates tissue inhibitor of metalloproteinase-2 (TIMP-2) and downregulates NF-jB, SP-1 and AP-1 expression with consequent MMP-2 inhibition suppressing cell transition, cancer cell migration and invasiveness [245].

Aryl hydrocarbon receptor (AHR)
AHR is a cytosolic transcription factor with pro-and anti-inflammatory activity and serves as a central modulating receptor of inflammatory response [262]. AhR was discovered as a specific binding site to TCDD [263], inducing aryl hydrocarbon hydroxylase [264], with proven AHR induction by TCDD [265]. Later, it was proven that cytosolic AHR translocates temperature-dependent into the nucleus which is necessary to induce cytochrome P450 [266,267] and that aryl hydrocarbon receptor nuclear translocator (ARNT) is an essential dimerization partner for the AHR [268].
Constitutive NF-jB activation is increased in both breast cancer tissues and cell lines [290] and there is a direct association between the NF-jB subunit RelA and AHR in murine hepatoma cells [291]. Kim et al. showed in malignant and non-malignant breast cell lines, that RelA and AHR but not NF-jB RelB or c-Rel subunits build a transcription factor complex resulting in c-myc gene expression [292]. "The pleiotropic interleukin (IL)-6-type cytokine oncostatin M (OSM) is an inducer of AHR mRNA and protein expression in human HepG2 hepatocarcinoma cells" [293] and AHR-dependent IL-6 expression which is associated with IL-b1-induced binding of NF-jB components [294]. AHR-inhibition, but not cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1) inhibition, induces transcription factor p65 encoded by RELA gene (RelA), transcription factor encoded by the RELB gene interacting with NF-jB (RelB), nuclear factor kappalight-chain-enhancer of activated B cells 1 (NF-jB1), nuclear factor kappa-light-chain-enhancer of activated B cells 2 (NF-jB2) and MMP-1 promoting cancer invasiveness. Additionally, there is a different mechanism affecting 12-hydroxyeicosatetraenoic acid (12-HETE). Inhibiting NF-jB2 is associated with induced AHR, CYP1A1 and 12-HETE synthesis and both CYP1A1 and NF-jB can be inhibited in vitro by the alpha-2A adrenergic receptor (a 2A receptor) agonist guanfacine and ethyl apovincaminate (vinpocetine) [295].
AHR deletion was associated with "failure to control Citrobacter rodentium infection due to unrestricted intestinal stem cell (ISC) proliferation and impaired differentiation, culminating in malignant transformation" [296]. AHR deficiency is enhanced by chronic inflammation in colon carcinogenesis. Otherwise, AHR activation by AHR dietary ligands such as dietary components and tryptophan metabolites regulated intestinal crypt stem cell differentiation and was associated with prevention of carcinogenesis in mice through really interesting new gene (ring) finger protein 43 (Rnf43) and the cell-surface transmembrane E3 ubiquitin ligase zinc and ring finger 3 (Znrf3, homologue of Rnf43), E3 ubiquitin ligases with inhibition of Wntb-catenin signaling and consequent decrease of ISC proliferation. This may underpin the integrity role of AHR acting as a host defense [297].
Therapy with the AHR agonist TCDD in mice induced fibrosis markers (collagen 1A1 and a-smooth muscle actin), with increased interleukin-1 beta, tumor necrosis factor a and fibroblast activating fibroblast-specific protein 1 (FSP1, S100A4) together with an increase of TGF-b and Snail with an decrease of E-Cadherin and Claudin 1. The fibrosis was histologically apparent after 6 weeks [299]. As AHR knockout rats are insensitive to repeated TCDD exposure, AHR seems to be a regulator of fibrosis and carcinogenesis following TCDD treatment [300]. TCDD treatment at first increased rodent hepatic stem cells (rHpSCs) followed by a loss of loss of viability of hepatoblasts (rHBs) [301]. TCDD promotes cell transition through AHR-mediated EGFR/ERK signaling [302].
A catabolite of tryptophan, kynurenine (Kyn), was shown to be excessively produced by glioma cells through tryptophan-2,3-dioxygenase (TDO) with consequent binding and activation of AHR [303]. AHR was found to downregulate TGF-b signaling in non-neoplastic astrocytes and "constitutive AHR activity positively controls TGF-b1, TGF-b2 and latent TGF-b-binding protein-1 protein levels in malignant glioma cells" and AHR inhibition resulted in lower survival and invasiveness of glioma cells [304].
Recently AHR was reported to act as a repressor of inflammation associated in colon cancer [325]. These contradictory dictionary findings can be explained as was clearly shown that the concentration on one variable will not be enough to understand complexity and that AHR is involved in carcinogenesis but CYP isoforms will not be expressed in AHR knockdown mice AhR(À/À) mouse and that CYP1A1 is needed [318]. This reveals how just looking at findings in one knockout mouse model without simultaneously taking into account coactivator and/or associated other necessary variables and mediators will result in complete contradictionary findings and interpretations. Moreover, AHR negatively cross-talks with NF-jB but not with CYP1A1 [295]. The AHR ligand 6-formylindolo (3,2-b) carbazole (Ficz) is an AHR agonist in zebrafish inducing various CYP* such as CYP1A1, CYP1B1 [326] which explains why Ficz is protective against AHRmediated chronic inflammation and downregulates interleukin 7 (IL-7) and dextran sulfate sodium (DSS)-induced colitis in wild-type C57BL/6J mice [327]. We assume that assessing AHR can only be accomplished by taking into account the eicosanoid pathway and its cytochrome P450 pathway, including its many isoforms which has been reviewed in this Special Issue [30].
AHR-mediated carcinogenesis with the disruption of eicosanoid homeostasis as reviewed recently [30], is involved in breast cancer [328,329], colitis associated colon cancer through miR-132 expression after AHR activation by TCDD [330].
B[a]P induces AHR-dependent IL-10 increase with chronic inflammation [331] and AHR is involved in inflammatory fibrosis of the pancreas [332] and the liver [333]. It depends whether or not AHR is already translocated from its inactive cytoplasmic form to the nucleus.
L-kynurenine ((S)-2-Amino-4-(2-aminophenyl)-4-oxobutanoic acid) is a metabolite of the amino acid L-tryptophan through tryptophan dioxygenase in the liver and indoleamine 2,3-dioxygenase (IDO) by various human cells; IDO derived Kyn is an endogenous ligand of the human AHR, which is increased in chronic inflammation, promoting cancer cell survival and metastasis in brain cancer cells [303]. The D-enantiomer of kynurenine, D-kynurenine (D-Kyn), is increased in lung cancer cells and is associated with increased vimentin and increases in CYP1A1 and AHR nuclear translocation promoting cell transition [334]. Inactivating the dioxin-like polychlorinated biphenyl (PCB), PCB126, stimulates upregulation of ROS through AHR. Promoting cell transition is in this instance regulated through signal transducer and activator of transcription 3 (STAT3)/Snail1 which is dependent on pyruvate kinase M2 (PKM2) [335]. High expression of its members IDO, STAT3 and the AHR target gene CYP1B1 is associated with reduced relapse-free survival in lung cancer patients [336]. GSK-3b suppresses ESCC growth via STAT3 [337] but it seems that AHR is involved as well. Inactivating GSK-3b by the aminopyrimidine derivative CHIR-99021 reverses vimentin degradation in AHR overexpressed H1299 cells but it depends where AHR is increased/ activated. Cytoplasmatic (inactive) AHR suppresses cell transition via augmentation of mesenchymal vimentin level, and GSK-3b Ser-9 hyper-phosphorylation [338].
The AHR-TGF-b1 crosstalk is also complex. AHR can downregulate TGF-b1 signaling through latent transforming growth factor-beta binding protein 1 (LTBP-1) [339] or result in a deregulation of TGF-b1 secretion [340], but there is an association between AHR, TGF-b1 and the repetitive DNA sequence long interspersed nuclear element-1 (LINE1) which sheds a new light on carcinogenesis and cancer associated findings.

Long interspersed nuclear element-1 (LINE1)
Human transposable elements include RNA and DNA families, and RNA transposons (retrotransposons, retroelements) are divided into long-terminal repeat (LTR) LTR)containing or non-LTR groups and "The active, human non-LTR group includes LINE-1 (or L1), next to short interspersed elements (SINE) represented by Alu, and the more recently characterized SVA elements" and estimated some 45% of the human genome originates from transposable elements [341,342]. LINE1 "retrotransposons make up a significant portion of human genomes, with an estimated 500 000 copies per genome" [343].
LINE-1 is regulated and repressed in human tissue by DNA methylation [344][345][346][347] and "long-term NSAID use and a normal BMI were associated with increased LINE-1 DNA methylation" as well as a healthy life-style [348,349]. Chronic inflammation, oxidative stress, and environmental changes can induce and restore LINE-1 methylation [350][351][352][353] but not in gingival inflamed tissues [354]. LINE-1 is reactivated by the AHR agonist (B[a]P) through TGF-b1 signaling in human liver cancer samples "at various stages of malignant progression" [355].
The association of chronic inflammatory, environmental, oxidative stress and external pathogenic stimuli induced somatic LINE-1 restoration without the need of any mutations together with AHR and CYP* findings should cast a new light in the observed LINE-1 transpositions observed in various diseases and cancers.
"Factors belonging to the family of the testis-determining factor gene SRY (the SOX family)" regulate LINE-1 [367] and Dicer, which is downregulated by b-catenin and decreased in aggressive cancers [167], and which negatively regulates LINE-1 [368]. A LINE1 transcript "driven by an HBx promoter, referred to as HBx-LINE-1" activates Wnt/b-catenin signaling, promotes cell transition, and is expressed in HCC in mice and associated with poor survival and HBx-LINE-1 [369]. LINE1 inhibition results in altered cell morphology [370,371] and reversed cell transition (Fig. 2 from [372] not shown).

Chronic cell matrix stress
Activin A receptor like type (ALK) p120 selectively inhibits the small GTPase Ras homolog gene family, member A (RhoA) activity both in vitro and in vivo [375]. TGF-b1 induces cell transition via increased RhoA activity [376] which is dependent on activin receptor-like kinase 5 (ALK5) [377].
The transmembrane serine/threonine receptor kinase, activin A receptor like type 1 (ALK1), functions as an alternative type I receptor for TGF-b and increases in ALK1 occur due to elevated MMP-13. The interaction between ALK1 and the TGF-b type I receptor activin-like kinase 5 (TbRI or ALK5) with its ALK1/ALK5 ratio is age-related with a shift to decreased ALK5 in aged mice [378]. ALK1 signaling via MMP-13 results in type II collagen degradation. In young animals, ALK5 is protective of collagen degradation but during aging the ALK1/ALK5 ratio changes as does the role of TGF-b. This maybe relevant as ALK1 is involved in angiogenesis [379] and lends credence to why anti-ALKL1 therapy may be useful in certain cancer therapies [380].
Protein 120 (p120, catenin delta-1) The shift in localization of protein 120 (p120, catenin delta-1) was associated with a decrease in RhoA activation, and E-cadherin loss which resulted in decreased mobility of cells [381]. In p53-deficient mice, the tumor suppressor p120 "is dominant over E-cadherin inactivation and its inactivation promotes the development of basal, EMT-type invasive mammary tumors" [382]. Due to an increase of TGF-b [383,384] and a decrease in E-Cadherin, the long isoform of p120 dissociates from the membrane and accumulates within the cytoplasm [385]. The p120 family shows redundancy including delta catenin (d-catenin, cadherin-associated protein 2, CTNND2, neural plakophilin-related arm-repeat protein, NPRAP), armadillo repeat protein deleted in velo-cardiofacial syndrome (ARVCF), armadillo protein p0071 (plako-phili4), the more distantly related plakophilins 1-3, which regulate cadherins important for cell-cell communication and for adhesion [386].
Ras is activated by epidermal growth factor (EGF) with consequent RAS movement from an inactive GDP-bound state to an active GTP-bound state [391]. p120 can increase Cdc42 and Rac without altering Rho activity [392]. It is considered that the localization of p120 affects cell motility. p120 activates Rac1/MAPK signaling in breast cancer cells [393] but p120 can also be regulated depending on cancer cell type and through inactivation of E-cadherin [394].
Increased cytoplasmic p120 levels were observed in invasive gastric cancer [395] and loss, or even p120 translocation into the cytoplasm, was associated with cancer and with disease progression [394]. H. pylori induced MMP-7 expression is regulated by p120 and Kaiso [396], which is "a novel member of the rapidly growing BTB/POZ (Broad complex, Tramtrak, Bric à brac/Pox virus and zinc finger) family of zinc finger (ZF) transcription factors (hereafter referred to as POZ-ZF proteins" [397]. The interaction between p120, Rho and cadherins is complex [398], as Rho increases, Rac activity increases through loss of p120 [399].
ECM remodeling through Rac and Cdc42 activation was shown in rat fibroblasts [400]. Silencing of the Rac1 gene results in increased degradation of the ECM, suggesting that Rac1 inhibitors might play an important role in cancer therapy [401]. Rac1 silencing in lung cancer cells was also associated with inhibition of NF-jB with a corresponding decrease in cell proliferation [402].
The ROS-mediated Src activation also increases tyrosine phosphorylation of p120-catenin with consequent p120 translocation [403]. As mentioned earlier, the p120 translocation and cytoplasmatic accumulation due to continuous TGF-b and LOX activation influence ECM remodeling and "this process may be seen as the starting point for the chronic-stress escape strategy as proposed" [22,31].

Summary
In nature, cells routinely undergo both de-differentiation and re-differentiation. The transition of one cell type to another, including its transition from one cell function to another is incompletely understood mechanistically. Science has learned from embryogenesis and morphogenesis that this biological process is routine and not an exception. The normal cell to cancer cell transition occurs when the necessary groundwork has been prepared by sequences that include pathogenic stimuli, chronic inflammation, remodeled fibrosis (PCN) and a failed chronic stress escape strategy (CSES) that results in a disruption of homeostasis essentially creating an imbalance of pro-and contra-cell transition conditions (Fig. 1). The multiplicity of pathways and signaling events that a cell, tissue, or organism can enlist to prevent or abort the transition from a normal to a cancer cell in a sequenced process that describes carcinogenesis does not need the invocation of somatic mutations. Many of the pathways and signaling mechanisms described involve biochemical processes that are a routine part of a dynamic homeostasis involved in growth and development. Thus, an overview of these complex inter-connected "Disruption of signaling homeostasis induced crosstalk in the carcinogenesis paradigm Epistemology of the origin of cancer" plays a key role in the development of cancer although current understanding does not permit a weightof-evidence risk assessment on the importance of any given signaling pathway or biochemical mechanism. Despite that limitation, the data strongly support crucial roles for inflammation and fibrosis via a PCN-sequenced event that comprises carcinogenesis.  Cyclin-dependent kinase inhibitor 1B P38

Acknowledgments
The manuscripts of this Special Issue were supported by the Theodor-Billroth-Academy Ò (TBA Ò ) and INCORE, (International Consortium of Research Excellence) of the (TBA Ò ). We express our gratitude to the discussions on the web group of the Theodor-Billroth-Academy Ò (TBA Ò ) on LinkedIn, the exchange with scientists at Researchgate.com, as well as personal exchanges with distinguished colleagues who stimulated our thinking all named individually earlier in publicationswe thank each one.

Conflict of Interest
The author reports the following conflict of interest: Björn LDM Brücher is Editor-in-Chief in Life Sciences-Medicine of 4open by EDP Sciences. Ijaz S. Jamall is Senior Editorial Board member in Life Sciences-Medicine of 4open by EDP Sciences. The authors, of their own initiative, suggested to the Managing Editorial to perform a transparent peer-review of their submittals. Neither author took any action to influence the standard submission and peer-review process, and report no conflict of interest. The authors alone are responsible for the content and writing of the manuscript of this Special Issue. This manuscript contains origi-gelatinases synthesis. J Immunol 178, 9,