Mechanisms of GTP-depletion induced apoptosis in HIT-T15 insulin-secreting cells

Abstract

Prolonged GTP depletion by mycophenolic acid (MPA) caused arrest of insulin-secreting beta-cells at G1 phase and triggered apoptosis in a dose- and time-dependent manner. Activation of caspase-2 was a critical event in this scenario, although it also involved activation of other caspases (caspase-3 and -9) and release of cytochrome c from mitochondria. In addition, the time course of MPA-induced apoptosis was closely correlated with the increase in tissue transglutaminase (tTG) activity. However, it appeared that tTG was only restricted to some terminal morphological changes but not responsible for the initiation of the cell death. Importantly, p21WAF1/CIP1 (a cyclin-dependent-kinase inhibitor) was elevated by MPA treatment independent of p53, an event preceding and well associated with caspase activation. A close relationship between p21WAF1/CIP1 and caspase activation/apoptosis was also observed when a p21WAF1/CIP1 inducer was studied. Thus these results indicate that p21WAF1/CIP1 may act as an upstream signal to activate caspases and in turn induce apoptosis subsequent of impaired mitogenesis due to sustained GTP-depletion.