Selective Roles of Retinoic Acid Receptor and Retinoid X Receptor in the Suppression of Apoptosis by All-trans-retinoic Acid

Retinoic acids exert profound effects on many biological processes including cell proliferation, differentiation, and morphogenesis. We previously reported that all- trans -retinoic acid (t-RA) protected mesangial cells from H 2 O 2 -triggered apoptosis by suppressing the activator protein 1 (AP-1) pathway. It was via inhibition of c- fos and c- jun expression and suppression of c-Jun N-terminal kinase (JNK) activation. In this report, we investigated the involvement of retinoic acid receptor (RAR) and retinoid X receptor (RXR) in the antiapoptotic effect of t-RA in H 2 O 2 -exposed cells. We found that pretreatment with RAR pan-antagonist (AGN193109) or RXR pan-antagonist (HX531) attenuated the antiapoptotic effect of t-RA. Similarly, transient transfection with a dominant-negative mutant of RAR or a dominant-negative RXR diminished the antiapoptotic effect of t-RA. Both RAR and RXR antagonists reversed the suppressive effect of t-RA on AP-1 activity. However, the roles of RAR and RXR in the suppression of AP-1 components by t-RA were found to be different. RAR antagonist reversed the suppressive effect of t-RA on both c- fos and c- jun , whereas RXR antagonist reversed the effect of t-RA on c- fos but not c- jun . Furthermore, suppression of JNK activation by t-RA was observed even in the presence of RAR and RXR antagonists. Consistently, suppression of JNK by t-RA was not affected by overexpression of either the dominant-negative RAR or the dominant-negative RXR. These data elucidated that the antiapoptotic effect of t-RA is mediated by both nuclear receptor-dependent and -independent mechanisms.