Overexpression of CD133 enhances chemoresistance to 5-fluorouracil by activating the PI3K/Akt/p70S6K pathway in gastric cancer cells

CD133 has been reported to be associated with chemoresistance in various cancer cells. The efficacy of 5-fluorouracil (5-FU), an important chemotherapeutic agent for advanced gastric cancer (GC), is limited by 5-FU resistance. Hence, the present study investigated the function of CD133 in 5-FU resistance in human GC cells. We isolated CD133(+) GC cells by immunomagnetic cell sorting and CD133 expression was modulated by transfection of CD133 gene or CD133 small interfering ribonucleic acid. To assess the 5-FU cytotoxicity, Cell Counting Kit-8 was used. Expression of CD133, P-glycoprotein (P-gp), B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), phospho-Akt (p-Akt) and phospho-p70S6 kinase (p-p70S6K) were analyzed by western blotting. CD133, P-gp, Bcl-2 and Bax messenger ribonucleic acids were evaluated using semi-quantitative reverse transcriptase-polymerase chain reaction. Cell apoptosis was assessed by Hoechst 33258 staining. CD133(+) cells were more resistant to 5-FU than CD133(-) cells, and showed higher expression of P-gp and Bcl-2 with lower expression of Bax. Furthermore, CD133 silencing enhanced 5-FU cytotoxicity and apoptotic characteristics, whereas CD133 overexpression increased 5-FU resistance. CD133 silencing and activation directly decreased and increased the expression of P-gp, Bcl-2, p-Akt and p-p70S6K, respectively. Notably, Akt inhibition by LY294002 restored the 5-FU cytotoxicity suppressed by CD133 overexpression, while Akt activation by epidermal growth factor reversed the 5-FU cytotoxicity enhanced by CD133 silencing. Therefore, CD133 may inhibit 5-FU-induced apoptosis by regulating the expression of P-gp and Bcl-2 family mediated by phosphoinositide 3-kinase/Akt/p70S6K pathway in GC cells.