LXR?-mediated Downregulation Of EGFR Suppress Colorectal Cancer Cell Proliferation

Background: A varies of studies have found that LXR? inhibits proliferation ability of several cancer cells,but the role of LXR? in colorectal cancer cells and its mechanism by which LXR? regulates colorectal cancer cells proliferation is still unclear.Methods: The expression of LXR? in 20 paired CRC and adjacent tissues was detected by qRT-PCR.Immunohistochemistry was used to detect the expression of LXR? in tissues of CRC patients and to analyze the relationship between LXR? expression and clinical features of patients.Further,the expression of LXR? protein was detected in CRC tissue samples.The effects of LXR? on the biological function of colorectal cancer cells were examined by flow cytometry,CCK-8 assay and clone formation assay with the use of GW3965.The potential downstream genes of LXR? were detected by qRT-PCR and Western blot,and the downstream target genes regulated by LXR? were identified.The effect of interfering with EGFR on the biological function of colorectal cancer was studied.The correlation of LXR? expression was analyzed in colon cancer cell lines.The potential binding sites of LXR? in EGFR promoter(-2000 to + 100)region were predicted by bioinformatics analysis.The regulatory relationship between LXR? and EGFR promoter(-2000 to + 100)region was detected by double luciferase assay.We constructed a nude mouse model to detect the effect of LXR? expression on the growth of transplanted tumors in nude mice,and to verify the regulation of EGFR by LXR? in transplanted tumors in nude mice.Results: By using qRT-PCR and Western blot,we found that the expression of LXR? was higher in normal tissues adjacent to cancer than in cancer tissues,and the expression level of LXR? was correlated with clinic pathological features such as the size of tumors in clinical patients.We found that up-regulation of LXR? increased the inhibitory effect of LXRs agonist GW3965 on the proliferation of colon cancer cells,and decreased the inhibitory effect of GW3965 on the proliferation of colon cancer cells after interfering with LXR? in vitro.These results suggest that the inhibitory effect of GW3965 on the proliferation of colorectal cancer is mediated by LXR?.LXR? is a transcription factor which can regulate the expression of many cancer-related genes including FOXM1.We found that LXR? could inhibit the mRNA expression of EGFR in colorectal cancer cells by using qRT-PCR.Bioinformatics analysis revealed that LXR? could bind to multiple regions of EGFR promoter(-2000 to + 100).The inhibitory effect of LXR? on the activity of EGFR promoter was verifiedby double Luciferase Report experiment.The negative regulation effect of LXR? on EGFR was also verified in nude mice.Conclusions: LXR? can inhibit the expression of EGFR by inhibiting the promoter activity of EGFR,thus inhibiting the proliferation of colorectal cancer cells.