Bcl-2 and Bax exert opposing effects on Ca2+ signaling, which do not depend on their putative pore-forming region.
Recent work has shown that Bcl-2 and other anti-apoptotic proteins partially deplete the endoplasmic reticulum (ER) Ca(2+) store and that this alteration of Ca(2+) signaling reduces cellular sensitivity to apoptotic stimuli. We expressed in HeLa cells Bcl-2, Bax, and Bcl-2/Bax chimeras in which the putative pore-forming domains of the two proteins (alpha 5-alpha 6) were mutually swapped, comparing the effects on Ca(2+) signaling of the two proteins and relating them to defined molecular domains. The results showed that only Bcl-2 reduces ER Ca(2+) levels and that this effect does not depend on the alpha 5-alpha 6 helices of this oncoprotein. Soon after its expression, Bax increased ER Ca(2+) loading, with ensuing potentiation of mitochondrial Ca(2+) responses. Then the cells progressed into an apoptotic phenotype (which included drastic reductions of cytosolic and mitochondrial Ca(2+) responses and alterations of organelle morphology). These results provide a coherent scenario that high-lights a primary role of Ca(2+) signals in deciphering apoptotic stimuli.
Chami
Mounia
M
Department of Experimental and Diagnostic Medicine, Section of General Pathology and the Interdisciplinary Center for the Study of Inflammation, University of Ferrara, 44100 Ferrara, Italy.
Prandini
Andrea
A
Campanella
Michelangelo
M
Pinton
Paolo
P
Szabadkai
Gyorgy
G
Reed
John C
JC
Rizzuto
Rosario
R
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000331:Aequorin / Q000235:genetics; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism*; D003001:Cloning, Molecular; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D006367:HeLa Cells; D006706:Homeostasis; D006801:Humans; D008928:Mitochondria / Q000378:metabolism / Q000648:ultrastructure; D017433:Protein Structure, Secondary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000502:physiology; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014162:Transfection; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D051028:bcl-2-Associated X Protein; D000331:Aequorin; D000255:Adenosine Triphosphate; D002118:Calcium