A Ca2+ signal is found upstream of cytochrome c release during apoptosis in HeLa cells |
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Authors: | Pu Yongmei Luo Kathy Q Chang Donald C |
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Institution: | Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China. |
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Abstract: | 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. |
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Keywords: | Ca2+ signal Ca2+ spikes Apoptosis Programmed cell death Cytochrome c release |
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