Stimulatory heterotrimeric GTP-binding protein augments cisplatin-induced apoptosis by upregulating Bak expression in human lung cancer cells

Abstract

The present study aimed to investigate the effect of the stimulatory heterotrimeric GTP-binding (Gs) protein signaling system on cisplatin-induced apoptosis of lung cancer cells and its underlying mechanism as an attempt to develop a novel strategy to improve the therapeutic efficacy of cisplatin. Overexpression of the constitutively active alpha subunit of Gs (G alpha sQL) in A549 human lung cancer cells increased cisplatin-induced apoptosis, and knockdown of G alpha s with small hairpin RNA decreased the percentage of apoptotic cells. G alpha sQL increased the expression of the proapoptotic proteins B-cell leukemia/lymphoma-2 genes (Bcl-2) homologous antagonist killer protein (Bak) and Bcl-2 associated X protein (Bax), and decreased the expression of the antiapoptotic proteins Bcl-2 and Bcl-Xlong protein. Knockdown of Bak blocked the augmentative effects of G alpha sQL. G alpha sQL decreased the degradation rate of the Bak protein, and increased Bak mRNA transcript levels. G alpha sQL increased Bak-luciferase activity in a protein kinase A and cyclic AMP response element-dependent manner. G alpha sQL also augmented cisplatin-induced apoptosis of H1299 human lung cancer cells that lack functional p53. From this study, it is concluded that G alpha s augments cisplatin-induced apoptosis of lung cancer cells partially through upregulating Bak expression by increasing transcription and by decreasing the rate of protein degradation. (Cancer Sci 2009; 100: 1069-1074).