A Novel Role for Bcl-2 in Regulation of Cellular Calcium Extrusion

The antiapoptotic protein Bcl-2 [1, 2] plays important roles in Ca(2+) signaling [3] by influencing inositol triphosphate receptors and regulating Ca(2+)-induced Ca(2+) release [4–6]. Here we investigated whether Bcl-2 affects Ca(2+) extrusion in pancreatic acinar cells. We specifically blocked the Ca(2+) pumps in the endoplasmic reticulum and assessed the rate at which the cells reduced an elevated cytosolic Ca(2+) concentration after a period of enhanced Ca(2+) entry. Because external Ca(2+) was removed and endoplasmic reticulum Ca(2+) pumps were blocked, Ca(2+) extrusion was the only process responsible for recovery. Cells lacking Bcl-2 restored the basal cytosolic Ca(2+) level much faster than control cells. The enhanced Ca(2+) extrusion in cells from Bcl-2 knockout (Bcl-2 KO) mice was not due to increased Na(+)/Ca(2+) exchange activity, because removal of external Na(+) did not influence the Ca(2+) extrusion rate. Overexpression of Bcl-2 in the pancreatic acinar cell line AR42J decreased Ca(2+) extrusion, whereas silencing Bcl-2 expression (siRNA) had the opposite effect. Loss of Bcl-2, while increasing Ca(2+) extrusion, dramatically decreased necrosis and promoted apoptosis induced by oxidative stress, whereas specific inhibition of Ca(2+) pumps in the plasma membrane (PMCA) with caloxin 3A1 reduced Ca(2+) extrusion and increased necrosis. Bcl-2 regulates PMCA function in pancreatic acinar cells and thereby influences cell fate.