Background Increased risk of bladder cancer has been reported in diabetic patients. This study was to investigate the roles of mitogen-activated protein kinase kinase （MEK） 1 and 2 in the regulation of human insulin- and insulin glargine-induced proliferation of human bladder cancer T24 cells. Methods In the absence or presence of a selective inhibitor for MEK1 （PD98059） or a specific siRNA for MEK2 （siMEK2）, with or without addition of insulin or glargine, T24 cell proliferation was evaluated by cell counting kit （CCK）-8 assay. Protein expression of MEK2, phosphorylation of ERK1/2 and Akt was analyzed by Western blotting. Results T24 cell proliferation was promoted by PD98059 at 5-20 IJmol/L, inhibited by siMEK2 at 25-100 nmol/L. PD98059 and siMEK2 remarkably reduced phosphorylated ERKI/2. Insulin- and glargine-induced T24 cell proliferation was enhanced by PD98059, suppressed while not blocked by siMEK2. Insulin- and glargine-induced ERKI/2 activation was blocked by PD98059 or siMEK2 treatment, whereas activation of Akt was not affected. Conclusion MEK1 inhibits while MEK2 contributes to normal and human insulin- and insulin glargine-induced human bladder cancer T24 cell proliferation.
LIU Shan-yingLIANG YingLIN Tian-xinSU FangLIANG Wei-wenUwe HeemannLI Yan
Background Increased levels of plasma lipopolysaccharide （LPS） have been found in obesity and diabetes patients. This study was to investigate the effect of LPS on pancreatic beta-cell viability and the involvement of caspase 3 in NIT-1 cell line. Methods Mouse insulinoma NIT-1 cells were treated with LPS for the indicated time and dose. Cell viability was measured by cell counting kit-8 reagent. Toll-like receptor 4 （TLR4）, caspase 3 and cleaved caspase 3 were detected by Western blotting. Insulin was determined by radioimmunoassay （RIA）. Results LPS promoted NIT-1 cell proliferation at 1 μg/ml, peaked at 72 hours of incubation. A reduction in cleavage of caspase 3 was observed upon LPS treatment. Bay11-7082, a specific inhibitor of nuclear factor （NF）-κB, blunted LPS-induced inhibition of caspase 3 cleavage. Reduction in chronic insulin secretion was observed after treatment with LPS at 1 μg/ml for 48 and 72 hours, not for 24 hours. TLR4 protein was upregulated when NIT-1 cells were treated with LPS at 1 μg/ml for 24 hours. Conclusions LPS promotes early NIT-1 cell proliferation in association with NF-KB-mediated inhibition of caspase 3 cleavage. LPS exerts a time-dependent inhibitory effect on chronic insulin secretion from NIT-1 cells.
LIU Shan-ying LIANG Qi-jun LIN Tian-xin FAN Xin-lan LIANG Ying Uwe Heemann LI Yan
