Loss of Soluble N-Ethylmaleimide-sensitive Factor Attachment Protein α (αSNAP) Induces Epithelial Cell Apoptosis via Down-regulation of Bcl-2 Expression and Disruption of the Golgi

Intracellular trafficking represents a key mechanism that regulates cell fate by participating in either prodeath or prosurvival signaling. Soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein alpha (alpha SNAP) is a well known component of vesicle trafficking machinery that mediates intermembrane fusion. alpha SNAP increases cell resistance to cytotoxic stimuli, although mechanisms of its prosurvival function are poorly understood. In this study, we found that either siRNA-mediated knockdown of alpha SNAP or expression of its dominant negative mutant induced epithelial cell apoptosis. Apoptosis was not caused by activation of the major prodeath regulators Bax and p53 and was independent of a key alpha SNAP binding partner, NSF. Instead, death of alpha SNAP-depleted cells was accompanied by down-regulation of the antiapoptotic Bcl-2 protein; it was mimicked by inhibition and attenuated by overexpression of Bcl-2. Knockdown of alpha SNAP resulted in impairment of Golgi to endoplasmic reticulum (ER) trafficking and fragmentation of the Golgi. Moreover, pharmacological disruption of ER-Golgi transport by brefeldin A and eeyarestatin 1 or siRNA-mediated depletion of an ER/Golgi-associated p97 ATPase recapitulated the effects of alpha SNAP inhibition by decreasing Bcl-2 level and triggering apoptosis. These results reveal a novel role for alpha SNAP in promoting epithelial cell survival by unique mechanisms involving regulation of Bcl-2 expression and Golgi biogenesis.