The Molecular Mechanism For Activation Of NF-kappaB Signal Pathway And The Occurrence Of Colorectal Cancer

Colorectal cancer(CRC)is one of the leading causes of cancer-related deaths worldwide.Local invasiveness and distant metastasis are the leading causes of mortality associated with CRC.The molecular pathogenesis remains to be further elucidated.Recent advances in large-scale sequencing and other genomic analyses of human colorectal tumors have offered new opportunities for further characterization of molecular mechanisms of CRC proliferation and progression.NF-?B signaling pathway was deemed as a novel one.NF-?B signaling pathway plays an essential role in proliferation,development,and survival in both normal and a variety of cancer tissues.APRIL(a proliferation-inducing ligand)is a member of the tumor necrosis factor(TNF)superfamily and a cytokine that can stimulate cellular proliferation.APRIL is highly expressed in cancer tissues such as colon carcinoma and pancreatic cancer.APRIL can activate the canonical NF-?B signaling by cross-linking to the TNF receptor TACI(TNFRSF13B).E-cadherin is a member of transmembrane glycoproteins that mediates calcium-dependent cell-cell adhesion in epithelial tissues.E-cadherin,which blocks tumor cell invasion by restraining cells and preventing cell movement,is negatively regulated by the transcriptional repressor Snail,and stabilization of Snail is dependent on activation of NF-B signaling.A proliferationinducing ligand(APRIL)is highly expressed in colorectal cancer(CRC)tissues and cell lines.In this study,we tested the hypothesis that APRIL-p65 NF-B-Snail signaling regulates E-cadherin in CRC.We found that expression of Snail was inversely related to that of E-cadherin in CRC tissues and colon carcinoma cell line T84.In addition,APRIL treatment induced Snail at protein level only but not mRNA level,and COP9 signalosome subunit 2(CSN2)that acts to block ubiquitination and degradation of Snail at both mRNA and protein levels.Similarly,depletion of p65 by siRNAs led to up-regulation of Snail at protein level only,but not at mRNA level in T84 cells.Moreover,silencing of Snail resulted in decrease of E-cadherin at both protein andmRNA levels.These results suggest that APRIL-p65 NF-?B-Snail signaling plays a critical role in regulation of E-cadherin and provide insights into mechanisms for paracrine inflammation-induced metastasis in CRC.Cell proliferation is pivotal in tumorigenesis and cyclooxygenases(COXs)are important regulatory enzymes in this process.COXs catalyze the conversion of free arachidonic acid into prostaglandin(PG)H2,which is the precursor of other prostaglandins and thromboxanes.PGs play a role in various biological processes such as cell proliferation,angiogenesis,immune function and inflammation,which are all crucial in the development or progression of neoplasm.The human COX family includes three members,COX 1,COX 2 and COX 3.COX-2 plays an important role in the development of metaplastic and dysplastic tissue,as well as in the development and progression of cancer.COX-2 is believed to regulate cell proliferation,cell transformation,tumor growth,tumor metastasis and invasion.Tumors with high levels of COX-2 are more invasive and patients with those tumors had a significantly reduced survival.Inhibition of COX-2 regulation can help to control cancer proliferation and invasiveness.NF-kB is a key regulator in production of COX-2 in multiple types of tissues.Activated NF-?B can functions as an important regulator of inflammation and immune responses by mediating the expression of proinflammatory genes including chemokines,cytokines,adhesion molecules and growth factors.Furthermore,the targets of NF-?B are also important regulators of cell proliferation.The mechanism(s)regulating COX-2 in colorectal cancer remain poorly defined.In this study,we investigate the regulatory mechanisms of COX-2 expression in human colon cancer tissues and human colon carcinoma cell line LS174 cell line.We find that constitutively activated RelB/nuclear factor-?B2(NF-?B)-2(p52)acts as an endogenous stimulatory signal to regulate COX-2 by binding to a previously described NF-?B enhancer of COX-2 gene promoter.COX-2 was remarkably increased in colon cancer tissues,compared with those normal ones in immunohistochemistry.Increased nuclear import of Rel B and p52 was also observed in colon cancer tissues and colon carcinoma cell line LS174.Chromatin immunoprecipitation assay determined that COX-2 gene associated with both Rel B and p52.Luciferase reporter assay determined that the NF-?B enhancer of COX-2was sufficient to regulate transcriptional activity of a heterologous promoter in LS174 cells.RNA interference-mediated knockdown of RelB or p52 resulted in significant inhibition of COX-2 at both mRNA and protein levels in LS174 cells.Taken together,these results suggest that the both canonical and non-canonical NF-?B signaling pathway may be a novel drug target for treatment of colon cancer.