A Ca2+ signal is found upstream of cytochrome c release during apoptosis in HeLa cells.
We showed previously that a cytosolic Ca(2+) signal is involved in regulating UV-induced apoptosis in HeLa cells. In this study, we found evidence that this Ca(2+) signal occurs upstream of the release of cytochrome c from mitochondria. First, when we abolished [Ca(2+)](i) increases by injecting BAPTA or heparin into UV-treated HeLa cells, cytochrome c release was either blocked or severely delayed. Second, using a living cell imaging technique, we observed a series of transient [Ca(2+)](i) increases (typically lasting about 40-60s) in many apoptotic cells induced by either UV- or TNFalpha-treatment. Third, using GFP-tagged cytochrome c, we found that the Ca(2+) spikes appear in a time window before cytochrome c was released. Finally, by fixing the TNFalpha-treated cell at the time when it started to display Ca(2+) spikes, we examined the distribution of its endogenous cytochrome c using immunostaining. We found that cytochrome c was not yet released from mitochondria. These findings suggest the existence of certain apoptotic pathways, in which an early Ca(2+) signal is activated upstream of cytochrome c release.
Pu
Yongmei
Y
Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Luo
Kathy Q
KQ
Chang
Donald C
DC
D017209:Apoptosis; D020013:Calcium Signaling; D003574:Cytochrome c Group / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D006367:HeLa Cells; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014466:Ultraviolet Rays
D003574:Cytochrome c Group; D014409:Tumor Necrosis Factor-alpha; D004533:Egtazic Acid; D006493:Heparin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid