Bcl-2 acts subsequent to and independent of Ca2+ fluxes to inhibit apoptosis in thapsigargin- and glucocorticoid-treated mouse lymphoma cells.
The mechanism by which Bcl-2 inhibits apoptosis is unknown. One proposal is that Bcl-2 regulates intracellular Ca2+ fluxes thought to mediate apoptosis. In the present study, we investigated Bcl-2's mechanism of action by determining the effect of Bcl-2 on intracellular Ca2+ fluxes in the WEHI7.2 mouse lymphoma cell line, which does not express Bcl-2, and its stable transfectant, W.Hb12, which expresses a high level of Bcl-2. Treatment with the endoplasmic reticulum Ca(2+)-ATPase inhibitor thapsigargin produced marked alterations in intracellular Ca2+ homeostasis in both WEHI7.2 and W.Hb12 cells, including elevation of free cytosolic Ca2+, endoplasmic reticulum Ca2+ pool depletion, capacitative entry of extracellular Ca2+, and increased loading of Ca2+ into mitochondria. Similar changes in intracellular Ca2+ occurred spontaneously in both cell lines following exponential growth. In both situations, W.Hb12 cells maintained optimal viability despite marked alterations in intracellular Ca2+, whereas WEHI7.2 cells underwent apoptosis. Treatment with the glucocorticoid hormone, dexamethasone, induced apoptosis in WEHI7.2 cells, but not in W.HB12 cells, even though dexamethasone treatment did not alter intracellular Ca2+ homeostasis in either cell line. These findings indicate that Bcl-2 acts downstream from intracellular Ca2+ fluxes in a pathway where Ca(2+)-dependent and Ca(2+)-independent death signals converge.
Distelhorst
C W
CW
Department of Medicine, Case Western Reserve University, Cleveland, Ohio, USA. cwd@po.cwru.edu
McCormick
T S
TS
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002470:Cell Survival; D003600:Cytosol / Q000737:chemistry / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019254:Genes, bcl-2 / Q000235:genetics*; D005938:Glucocorticoids / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D008223:Lymphoma / Q000235:genetics / Q000503:physiopathology*; D051379:Mice; D013696:Temperature; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection / Q000235:genetics; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D005938:Glucocorticoids; D019284:Thapsigargin; D003907:Dexamethasone; D002118:Calcium