NF-κBp65 Modulates HTERT Expression In HepG₂ Cell

Background:The incidence of hepatocellular carcinoma (HCC) is rising in North America, Europe and Eastern countries such as China and Japan. Interestingly,90% of HCC cases have a natural history of unresolved inflammation and fibrosis or cirrhosis. Approaches to HCC prevention should therefore focus on the molecular regulators of a disease process that has been termed by some authors as the inflammation-fibrosis-cancer (IFC) axis. As NF-κB has been the focus of the transcription and expression of various genes coding for cytokines, enzymes, apoptosis, proliferation and adhesion molecules which have been implicated in inflammation and tumorigenesis. including those of the liver. A growing of evidence suggests that activation of NF-κB negatively regulates apoptotic event in cancer cells, although classical pro-apoptotic role is still suggested.As these cancers progress, telomerase activation may function to restore a level of chromosomal stability required for cancer cell viability. Although up-regulation of hTERT gene expression has been observed in various cancer cells, including hepatoma carcinoma cell. How telomerase reactivation is controlled during hepatocarcinogenesis are not well definedThe NF-κB and human telomerase reverse transcriptase gene (hTERT) are frequently deregulated and overexpressed in malignancy. Formerly report demonstrated that NF-κB positively regulates hTERT transcription and demonstrated that its effects on hTERT gene expression through the repression of the hTERT promoter activity. Furthermore, NF-κB modulated cytoplasmic to nuclear translocation of hTERT protein. To date, however, whether the NF-κB impacts on hTERT protein synthesis remains to be investigated. Blockade of NF-κB or regulation of the activation status of hTERT and may offer considerable therapeutic value in the treatment of apoptotic event in cancer cells. Objective:To explore LPS as well as MG-132 has effect on NF-κB p65-induced hTERT expression both at transcriptional levels and post-transcriptional levels and Dexamethasone modify LPS stimulated NF-κB p65 and hTERT expression in HepG2 cells.Methods:The expression of hTERT gene and NF-κB gene was analyzed using RT-PCR. Western blot was used to determine protein expression of hTERT. NF-κB activity was measured using immunofluorescent microscopy.Results:Our data clearly showed that MG-132 inhibited the expression of NF-κB gene and hTERT gene in a dose-dependent manner. Meanwhile, LPS upregulated NF-κB expression and hTERT gene.The inhibitor of dexamethasone inhibited such effects of LPS-induced NF-κB and hTERT expresstion.Conclusions:Here, we show that LPS (specific binding to TLR4 to activate NF-κB) were positive for NF-κB p65 mRNA expression and activation, up-regulates the level of hTERT mRNA expression and protein at 36h in a dose-dependent manner. In contrast, MG-132(blocking the activity of 26S proteasome and thereby prevents nuclear translocation of NF-κB) significantly inhibited the NF-κB activation and the mRNA expression, the level of hTERT mRNA and protein at 36h in a dose-dependent manner. Furthermore, Dexamethasone inhibited LPS-induced NF-κB activation and expression of hTERT in HepG2 cells in vitro. These findings suggest that NF-κB could modulate hTERT at transcription level in HepG2 cells, importantly, in translation level and that dexamethasone inhibits LPS-induced hTERT via blocking NF-κB.