Gianni, M, Ponzanelli, I, Mologni, L, Reichert, U, Rambaldi, A, Terao, M, and Garattini, E
In the NB4 model of acute promyelocytic leukemia (APL), ATRA, 9-cis retinoic acid (9-cis RA), the pan-RAR and RARαselective agonists, TTNPB and AM580, induce growth inhibition, granulocytic differentiation and apoptosis. By contrast, two RXR agonists, a RARβ agonist and an anti-AP1 retinoid have very limited activity, ATRA- and AM580dependent effects are completely inhibited by RAR antagonistic blockade, while 9-cis RA-induced cell-growth-inhibition and apoptosis are equally inhibited by RAR and RXR antagonists. ATRA, 9-cis RA and AM580 cause upregulation of the mRNAs coding for pro-caspase-1, -7, -8, and -9, which, however, results in increased synthesis of only pro-caspase-1 and -7 proteins. These phenomena are associated with activation of pro-caspase-6, -7 and -8, cytochrome c release from the mitochondria, inversion of Bcl-2/Bax ratio and degradation of PML-RARα. Caspase activation is fundamental for retinoid-induced apoptosis, which is suppressed by the caspase-inhibitor z-VAD. [ABSTRACT FROM AUTHOR]