Endoplasmic reticulum stress enhances chemoresistance of glioma cell line U87 to temozolomide

Abstract

Objective To investigate the effect of endoplasmic reticulum stress on sensitivity of glioma cell line U87 to temozolomide (TMZ) and underlying mechanism. Methods (1) Glioma U87 cells were routinely cultured for 24 h in vitro; different concentrations of TMZ (0, 12.5, 25, 50, 100 μmol/L) were added to intervene the cell proliferation of U87 cells for 24 h; MTT method was used to detect the cellular proliferation inhibition rate, and half maximal inhibitory concentration (IC50) of TMZ was calculated; tunicamycin (TM) treatment (0, 2, 4, 8 μmol/L) was given to the cells for 6 h, and then, 50 μmol/L TMZ was given for 24 h, and cellular proliferation inhibition rate of U87 was detect by MTT method. (2) U87 cells were randomly divided into control group, TM group, TMZ group and TM+TMZ group; pretreatment of TM for 6 h was given to cells from TM group and TM+TMZ group; and 50 μmol/L TMZ was given to cells from TMZ group and TM+TMZ group; same amount of medium was given to cells from control group; 24 h after treatment, the apoptotic rate was examined by flow cytometry; Western blotting was used to detect the protein expressions of caspase-3, B-cell lymphoma 2 associated X protein (Bax), O-6-methlguanine-DNA methyltransferase (MGMT), glucose-regulated protein 78 (GRP78), and inositol-requiring enzyme 1 (IRE-1). Results (1) MTT showed that IC50 of TMZ was 50 μmol/L. As compared with that of 0 μmol/L TM+50 μmol/L TMZ group or 2 μmol/L TM+50 μmol/L TMZ group, the cellular proliferation inhibition rate of 4 μmol/L TM+50 μmol/L TMZ group and 8 μmol/L TM+50 μmol/L TMZ group was significantly decreased (P<0.05). (2) As compared with TMZ group, TM+TMZ group had significantly decreased apoptotic rate (46.98%±4.79% vs. 35.74%±4.09%), significantly decreased caspase-3 and Bax protein expressions, and significantly increased MGMT, GRP78 and IRE-1 protein expressions (P<0.05). Conclusion Endoplasmic reticulum stress can increase the resistance gene MGMT expression, decrease the chemotherapy sensitivity to TMZ, and induce chemoresistance of glioma cell line U87. Key words: Glioma; Endoplasmic reticulum stress; Temozolomide; O-6-methlguanine-DNA methyltransferase