Reduced capacitative calcium entry correlates with vesicle accumulation and apoptosis

A preneoplastic variant of Syrian hamster embryo cells, sup(+), exhibits de creased endoplasmic reticulum calcium levels and subsequently undergoes apo ptosis in low serum conditions (Preston, G, A, Barrett, J, C,, Biermann, J, A, and Murphy, E, (1997) Cancer Res. 57, 537-542). This decrease in endopl asmic reticulum calcium appears to be due, at least in part, to reduced cap acitative calcium entry at the plasma membrane. Thus we investigated whethe r inhibition of capacitative calcium entry per se could reduce endoplasmic reticulum calcium and induce apoptosis of cells. We find that treatment wit h either SKF96365 (30-100 mu M) Or cell-impermeant 1,2-bis(o-amino-5-bromop henoxy)ethane-N,N,N',N'-tetra-acetic acid (5-10 mM) is able to induce apopt osis of cells in conditions where apoptosis does not normally occur. Becaus e previous work has implicated vesicular trafficking as a mechanism of regu lating capacitative calcium entry, we investigated whether disruption of ve sicular trafficking could lead to decreased capacitative calcium entry and subsequent apoptosis of cells. Coincident with low serum-induced apoptosis, we observed an accumulation of vesicles within the cell, suggesting deregu lated vesicle trafficking, Treatment of cells with bafilomycin (30-100 nM), an inhibitor of the endosomal proton ATPase, produced an accumulation of v esicles, decreased capacitative entry, and induced apoptosis, These data su ggest that deregulation of vesicular transport results in reduced capacitat ive calcium entry which in turn results in apoptosis.