Bcl-2 inhibits c-fos induction by calcium

Abstract

Transient elevation of cytosolic Ca²⁺ induces the expression of a variety of genes involved in cell growth and transformation, including the early response gene c-fos. Previously, we reported that Bcl-2 inhibits the transient elevation of cytosolic Ca²⁺ induced by thapsigargin (TG), a selective inhibitor of the endoplasmic reticulum-associated Ca²⁺-ATPase. Therefore, to determine if the effect of Bcl-2 on cytosolic Ca²⁺ elevation modulates Ca²⁺ signaling, we investigated the induction of c-fos by TG in WEHI7.2 mouse lymphoma cells, control transfectants (WEHI7.2-neo), and transfectants that stably express a high level of Bcl-2 (W.Hb12 and W.Hb15). TG induced 20-fold elevation of c-fos mRNA in WEHI7.2 and WEHI7.2-neo cells, but c-fos mRNA induction by TG was only fivefold in W.Hb12 and W.Hb15 cells. In contrast, phorbol 12-myristate acetate induced marked c-fos mRNA elevation in both WEHI7.2 and W.Hb12 cells, indicating that the inhibitory effect of Bcl-2 is selective for induction of c-fos by Ca²⁺. To measure c-fos promoter activity, WEHI7.2 and W.Hb12 cells were transiently transfected with a c-fos promoter-luciferase reporter plasmid. TG induced c-fos promoter activity in WEHI7.2 cells, but not in W.Hb12 cells. In WEHI7.2 cells, the signal for c-fos induction by TG was cytosolic Ca²⁺ elevation, as the increase in both c-fos mRNA level and promoter activity were prevented by lowering extracellular Ca²⁺ concentration, a condition that inhibits cytosolic Ca²⁺ elevation by reducing the TG-mobilizable Ca²⁺ pool. In summary, the findings indicate that Bcl-2 regulates Ca²⁺ signaling.