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Cytosolic Ca(2+) signal is involved in regulating UV-induced apoptosis in hela cells
1Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
Abstract:
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.
Insights
Cytosolic calcium (Ca2+) elevation is crucial for apoptosis progression. Unlike BAPTA/AM, membrane-impermeant BAPTA and heparin blocked apoptosis, indicating Ca2+ signaling
Area of Science:
- Cell Biology
- Biochemistry
Background:
- Recent studies using BAPTA/AM have questioned the role of Ca(2+) signaling in apoptosis.
- BAPTA/AM's complex effects on subcellular Ca(2+) distribution complicate interpretation.
Purpose of the Study:
- To clarify the role of cytosolic Ca(2+) in apoptosis progression.
- To investigate the differential effects of various Ca(2+) signaling blockers.
Main Methods:
- UV-induced apoptosis in HeLa cells.
- Application of BAPTA/AM, membrane-impermeant BAPTA (via electroporation), and heparin.
- Monitoring of cell death and apoptosis progression.
Main Results:
- BAPTA/AM did not inhibit UV-induced apoptosis.
- Membrane-impermeant BAPTA and heparin significantly suppressed apoptosis.
- These blockers targeted cytosolic Ca(2+) elevation and ER Ca(2+) release, respectively.
Conclusions:
- Cytosolic Ca(2+) elevation is a key signal driving apoptosis progression.
- BAPTA/AM's ineffectiveness is likely due to its dual action on cytosolic and ER Ca(2+) levels.
- Targeting specific Ca(2+) signaling pathways is essential for understanding apoptosis.