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Intracellular Ca2+ pool content is linked to control of cell growth
1Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201.
Abstract:
A close correlation was observed between intracellular Ca2+ pool depletion and refilling and the onset of DNA synthesis and proliferation of DDT1MF-2 smooth muscle cells. The intracellular Ca2+ pump inhibitors 2,5-di-tert-butyl-hydroquinone (DBHQ) and thapsigargin (TG) specifically emptied identical inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ pools and both arrested cell growth at concentrations corresponding to Ca2+ pump blockade. However, an important distinction was observed between the two inhibitors with respect to their reversibility of action. Upon removal of DBHQ from DBHQ-arrested cells, Ca2+ pools immediately refilled, and 14 hr later cells entered S phase followed by normal cell proliferation; the time for entry into S phase was identical to that for cells released from confluence arrest. Although TG irreversibly blocked Ca2+ pumping and emptied Ca2+ pools, high serum treatment of TG-arrested cells induced recovery of functional Ca2+ pools in 6 hr (via probable synthesis of new pump); thereafter cells proceeded to S phase and normal cell proliferation within the same time period (14 hr) as that following release of DBHQ-arrested cells. The precise relationship between Ca2+ pump blockade and growth arrest indicates that Ca2+ pool emptying maintains cells in a G0-like quiescent state; upon refilling of pools, normal progression into the cell cycle is resumed. It is possible that a specific cell cycle event necessary for G0 to G1 transition depends upon signals generated from the InsP3-sensitive Ca2+ pool.
Insights
Intracellular calcium (Ca2+) pool depletion halts smooth muscle cell growth, but refilling allows cell cycle re-entry. This Ca2+ signaling is crucial for cell proliferation and progression from G0 to G1 phases.
Area of Science:
- Cell Biology
- Biochemistry
- Physiology
Background:
- Intracellular calcium (Ca2+) signaling plays a critical role in regulating various cellular processes, including cell proliferation.
- The inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ pool is a key component of cellular Ca2+ homeostasis.
- Understanding the precise mechanisms by which Ca2+ regulates cell cycle progression is essential for comprehending cell growth and development.
Purpose of the Study:
- To investigate the correlation between intracellular Ca2+ pool dynamics and the initiation of DNA synthesis and proliferation in DDT1MF-2 smooth muscle cells.
- To compare the effects of two distinct Ca2+ pump inhibitors, 2,5-di-tert-butyl-hydroquinone (DBHQ) and thapsigargin (TG), on Ca2+ pools and cell growth.
- To elucidate the role of Ca2+ pool refilling in the resumption of cell cycle progression.
Main Methods:
- Treatment of DDT1MF-2 smooth muscle cells with Ca2+ pump inhibitors DBHQ and TG.
- Monitoring of intracellular Ca2+ pool depletion and refilling.
- Assessment of DNA synthesis and cell proliferation following inhibitor removal or cellular recovery.
- Analysis of the reversibility of growth arrest induced by different Ca2+ pump inhibitors.
Main Results:
- Both D H Q and TG specifically depleted InsP3-sensitive Ca2+ pools, leading to cell growth arrest.
- DBHQ-induced arrest was reversible upon inhibitor removal, with immediate Ca2+ pool refilling and subsequent entry into S phase within 14 hours.
- TG-induced arrest, while initially irreversible, could be overcome by high serum treatment, restoring Ca2+ pools and enabling cell proliferation within the same timeframe.
Conclusions:
- Intracellular Ca2+ pool depletion maintains cells in a quiescent G0-like state.
- Refilling of Ca2+ pools is necessary for the resumption of normal cell cycle progression.
- A specific cell cycle event, potentially during the G0 to G1 transition, may depend on signaling from the InsP3-sensitive Ca2+ pool.