The cell proliferation and apoptosis were detected by MTT assay and flow cytometry. Caspases activity was determined spectrophotometricaly at 405 nm using a microtiter plate reader. Western blot and real-time PCR was used to assess the protein and mRNA expression. Immunoprecipitation was used to examine the protein–protein interactions.
CSTMP inhibited the proliferation and induced cell cycle arrest and apoptosis of A549 cells. Caspase3, 8, 9 and PARP-1 activation, and Bax/Bcl-2 ratio analyses demonstrated that the anti-cancer effect of CSTMP in A549 cells was mediated by promoting caspase- and mitochondria-dependent apoptosis. Furthermore, CSTMP induced ER stress in A549 cells as evidenced by elevated levels of GRP78, GRP94, CHOP, IRE1α, TRAF2, p-ASK1 and p-JNK, activation of caspase12 and 4, and enhanced formation of an IRE1α-TRAF2-ASK1 complex. Knockdown of IRE1α by siRNA suppressed activation of IRE1α, TRAF2, p-ASK1 and p-JNK in CSTMP treated A549 cells. In addition, the effects of CSTMP on the formation of an IRE1α-TRAF2-ASK1 complex, caspase- and mitochondria-dependent apoptosis were also reversed by IRE1α siRNA in A549 cells.
Collectively, we showed that CSTMP induced apoptosis of A549 cells were through IRE1α-TRAF2-ASK1 complex-mediated ER stress, JNK activation, and mitochondrial dysfunction. These insights on this novel compound CSTMP may provide a novel anti-cancer candidate for the treatment of NSCLC.