Cytosolic Ca(2+) signal is involved in regulating UV-induced apoptosis in hela cells.
Results of recent studies using BAPTA/AM have raised a serious question on whether Ca(2+) signal is truly involved in regulating the progression of apoptosis. To resolve this question, we examined the differential effects of three different Ca(2+) signaling blockers (BAPTA/AM, membrane-impermeant BAPTA, and heparin) on UV-induced apoptosis in HeLa cells. We found that although the membrane-permeable form of BAPTA (i.e., BAPTA/AM) could not inhibit cell death, the membrane-impermeant form of BAPTA, loaded into the cytosol by electroporation, clearly protected cells from entering apoptosis. Furthermore, when we injected heparin to block Ca(2+) release from the endoplasmic reticulum (ER) to cytosol, apoptosis was greatly suppressed. These findings strongly suggest that elevation of cytosolic Ca(2+) is part of the signal that drives the progression of apoptosis. The negative result of BAPTA/AM is probably due to its dual effect on subcellular Ca(2+) distribution; besides suppressing the Ca(2+) elevation in cytosol, BAPTA/AM can also enter into the ER to reduce the free Ca(2+) level there. The depletion of Ca(2+) in ER is believed to stimulate apoptosis and thus would counterbalance the protection effect of BAPTA/AM in suppressing the cytosolic Ca(2+) elevation.
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Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
Chang
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D017209:Apoptosis / Q000528:radiation effects*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D018274:Electroporation; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D014466:Ultraviolet Rays
D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium