Effect of mitogen-activated protein kinase signal transduction pathway on multidrug resistance induced by vincristine in gastric cancer cell line MGC803

AIM:To investigate the correlation between mitogen-activated protein kinase (MAPK) signal transduction pathway and multidrug resistance (MDR) in MGC803 cells.METHODS:Western blot was used to analyze the expression of MDR associated gene in transient vincristine (VCR) induced MGC803 cells, which were treated with or without the specific inhibitor of MAPK, PD098059.Morphologic analysis of the cells treated by VCR with or without PD098059 was determined by Wright-Giemsa staining. The cell cycle analysis was performed by using flow cytometric assay and the drug sensitivity of MGC803 cells which were exposed to VCR with or without PD098059 was tested by using MTT assay.RESULTS:Transient exposure to VCR induced P-gp butnot MRP1 or GST-π expression in MGC803 cells and the expression of P-gp was inhibited by PD098059.Apoptotic bodies were found in the cells treated with VCR or VCR+PD098059. FCM results indicated that more MGC803 cells showed apoptotic phenotype when treated by VCR and PD098059 (rate:31.23%) than treated by VCR only (rate:18.42%) (P<0.05).The IC50(284±13.2 μg/L) of MGC803 cells pretreated with VCR was 2.24-fold as that of negative control group (127±17.6μg/L) and 1.48-fold as that of the group treated with PD098059 (191±27.9μg/L).CONCLUSION:This study shows that the expression of P-gp can be induced by transient exposure to VCR and this induction can be prevented by PD098059, which can block the activity of MAPK. MAPK signal transduction pathway may play some roles in modulating MDR1 expression in gastric cancer.

Effect of staurosporine on cycle of human gastric cancer cells

AIM:To study the effect of staurosporine (ST) on the cell cycle of human gastric cancer cell lines MGC803 and SGC7901.METHODS:Cell proliferation was evaluated by trypan blue dye exclusion method.Apoptotic morphology was observed under a transmission electron microscope.Changes of cell cycle and apoptotic peaks of cells were determined by flow cytometry. Expression of p21^WAF1 gene was examined using immunohistochemistry and RT-PCR.RESULTS:The growth of MGC803 and SGC7901 cells was inhibited by ST.The inhibitory concentrations against 50% cells (IC50) at 24 h and 48 h were 54ng/ml and 23ng/ml for MGC803, and 61ng/ml and 37ng/ml for SGC7901.Typical apoptotic bodies and apoptotic peaks were observed 24h after cells were treated wth ST at a concentration of 200ng/ml.The percentage of cells at G0/G1 phase was decreased and that of cells at G2/M was increased significantly in the group treated wth ST at the concentrations of 40ng/ml,60ng/ml,100ng/ml for 24h,compared with the control group (P<0.01).The expression levels of p21^WAF1 gene in both MGC803 and SGC7901 cells were markedly up-regulated after treatment with ST.CONCLUSION:ST can cause arrest of gastric cancer cells at G2/M phase,which may be one of the mechanisms that inhibit cell proliferation and cause apoptosis in these cells.Effect of ST on cells at G2/M phase may be attributed to the up-regulattion of p21^WAF1 gene.