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.
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.
Mounia
M
Chami
Andrea
A
Prandini
Michelangelo
M
Campanella
Paolo
P
Pinton
Gyorgy
G
Szabadkai
John C
JC
Reed
Rosario
R
Rizzuto
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