B-lymphoma moloney murine leukemia virus insertion region 1 promotes epithelial-mesenchymal transition and invasion of colorectal cancer cell HT-29 cells in inflammatory microenvironment

Objective Investigate the effect and mechanism of B-lymphoma Moloney murine leukemia virus insertion region 1 (Bmi-1) on tumor migration and epithelial-mesenchymal transition (EMT) of HT-29 cells in inflammatory microenvironment. Methods Detect the gene and protein levels of Bmi-1, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) by qPCR and Western blotingt respectively, and the levels of TNF-α and IL-6 in culture medium supernatant by enzyme linked immunosorbent assay (ELISA). Evaluate the proliferation, migration and invasion in HT-29 cells by MTT assay and Transwell assays. EMT-related markers and nuclear factor-κB (NF-κB) pathway key proteins were detected by Western blotting. Results The mRNA levels of Bmi-1, TNF-α and IL-6 was significantly increased in HT29 cells after THP-1 Conditioned-Medium (THP-1-CM) stimulation (1.86±0.08 vs.1.00±0.05, 2.38±0.13 vs.1.00±0.14, 3.00±0.15 vs.1.00±0.05, P<0.01, respectively), as well as the protein levels[1.68±0.08 vs.1.00±0.05, (73±4) pg/ml vs. (32±4) pg/ml, (140±9) pg/ml vs. (42±9) pg/ml, P<0.01, respectively]. Knockdown of Bmi-1 expression remarkably repressed the secretion of cytokines[ (31±3), (56±8) pg/ml]. THP-1-CM accelerated the protein synthesis of vimentin, N-cadherin and phosphorylation of NF-κB, enhanced invasion and metastasis. Inversely, knockdown of Bmi-1 expression remarkably repressed THP-1-CM-induced EMT and NF-κB activity, but had no effect on cell proliferation in vitro. Conclusion Bmi-1 may be involved in the cytokines secretion of HT-29 cells induced by THP-1-CM, and has effect on migration and invasion through epithelial-mesenchymal transformation, which is related to NF-κB pathway activity. Bmi-1 can be treated as a potential molecular target for metastatic colorectal cancer. Key words: B-lymphoma moloney murine leukemia virus insertion region 1 gene; Tumor inflammatory microenvironment; Metastatic colorectal cancer