Objective: To investigate the expression of Toll-like receptor 7 (TLR7) in gastric cancer cell lines and the effect of imiquimod, a TLR7 agonist, on the proliferation and apoptosis of SGC-7901 cells.
Methods: The protein expression levels of TLR7 were detected with Western blotting in 3 human gastric cancer cell lines (SGC-7901, HGC-27 and MKN-28). The cell line expressing the highest TLR7 level was exposed to different doses of imiquimod for 12-72 h and the cell viability was assessed with MTT assay. The cell apoptosis rate after 100 µg/ml imiquimod treatment for 12 or 24 h was quantified by flow cytometry, and the ultrastructual changes of the cells were observed under electron microscope. The expression of apoptosis-related genes Bcl-2 and Bax were analyzed with real-time PCR.
Results: All the 3 cell lines expressed TLR7, among which SGC-7901 cells showed the highest expression level. TLR7 agonist imiquimod dose- and time-dependently reduced the viability of SGC-7901 cells. Exposure to 100 µg/ml imiquimod for 24 h resulted in SGC-7901 cell apoptosis as shown by an increased ratio of early apoptotic cells and significant ultrastructural changes of the cells. Real-time PCR demonstrated that imiquimod treatment for 24 h caused a dose-dependent reduction of Bcl-2 mRNA expression and increment of Bax mRNA expression.
Conclusions: TLR7 protein is expressed in all the 3 gastric cancer lines and its agonist imiquimod can inhibit cell proliferation and induce apoptosis in SGC-7901 cells.