025 The synthetic retinoid CD437 induces apoptosis in human respiratory epithelial cells, via mitochondrial and caspase-8-dependent pathways, both JNK up-regulated

Abstract

CD437 a synthetic retinoid-related molécule, sélective agonist of retinoic acid receptor RARγ is a potent chemo-therapeutic agent which induces apoptosis in numerous cell lines. Mechanisms of proapoptoic action of CD437 were studied in human epithelial airway respiratory cells, 16HBE transformed bronchial cell Une and normal nasal epithelial cells in primary culture ( Exp Cell Res 2005; 307: 76-90). Induction of apoptosis was investigated in respect with DNA fragmentation, cell cycle altération (PI and BrdU intégration), mitochondrial integrity (measure of membrane potential, immunodetection of mitochondrial proteins), activation of caspases and MAP kinases (sélective inhibitors). In both cell types, CD437 caused apoptosis in S-phase cells and cell cycle arrest in S phase. Apoptosis was abolished by cas-pase-8 inhibitor z-IETD-fmk which preserved S-phase cells, but was weakly inhibited by other sélective caspase-inhibitors, indica-ting that upstream caspase-8 activation was involved. The broad caspase inhibitor z-VAD and z-IETD prevented the nuclear envelope fragmentation, but did not block the chromatin condensation. Disruption of mitochondrial transmembrane potential was induced by CD437 treatment. The translocation of Bax to mitochondria and Bax activation were demonstrated, as well as the release of cyto-chrome-c into the cytosol, and of apoptosis-inducing factor (AIF) translocated into the nucleus. Z-VAD and z-IETD did not inhibit mitochondrial depolarization, Bax translocation or release of cyto-chrome-c and AIF from mitochondria. In addition, CD437 activated the JNK-MAP kinase signaling pathway, with the transient increase of AP-1 and c-jun expression. The use of JNK inhibitor suppressed mitochondrial depolarisation, caspase activation and subséquent S-phase cell apoptosis. Conver-sely, JNK pathway inhibition did not prevent CD437-induced cell cycle arrest. In human respiratory epithelial cells, transformed and primary cells, CD437-induced apoptosis is executed by two converging pathways both up-regulated by JNK: a caspase-indepen-dent mitochondrial pathway results in AIF release, responsible for chromatin condensation and first stage of apoptotis, and a caspase-8-dependent pathway triggers nuclear envelope fragmentation and final stage of apoptosis.