Gαs sensitizes human SH-SY5Y cells to apoptosis independently of the protein kinase A pathway

Disturbances in Gal-L levels and function have been implicated in the pathophysiology of bipolar disorder, but the role of these changes in the development of the illness is not clear. In view of the critical role of G alpha(s)-mediated cAMP signaling in regulating cell survival, we investigated the potential role of G alpha(s-L) in modulating susceptibility to cellular stressors in human SH-SY5Y neuroblastoma cells. Overexpression of Ga alpha(s-L) to a level twice that of the vector-transfected cells did not directly affect cell viability but significantly increased the sensitivity to induction of cell death by serum deprivation and other apoptotic stimuli, including staurosporine, H2O2, and tunicamycin. This enhanced sensitivity was associated with increased caspase-3 activation and appearance of fragmented nuclei (Hoechst 33342 staining). The broad-spectrum caspase inhibitor z-VADfmk completely suppressed cell death evoked by these apoptotic insults in both vector-transfected and G alpha(s-L)-overexpressing cells. The increased vulnerability conferred by increased Gas-L expression was neither mimicked by cAMP analogs 8-Br-cAMP, 8-CPT-cAMP, and 8-CPT-2Me-cAMP nor attenuated by PKA inhibitors Rp-cAMPS and KT5720. These data indicate that G alpha(s-L) may modulate apoptotic processes in a caspase-dependent manner through a signaling cascade that is independent of the cAMP/PKA or cAMP/Epac pathway. These results suggest that enhanced G alpha(s-L) expression, as was observed in post-mortem brain of bipolar patients, may impair cellular resilience in response to intracellular stress signals resulting from mitochondrial and/or endoplasmic reticulum dysfunction implicated in this disorder. (c) 2006 Wiley-Liss, Inc.