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Senescence marker protein-30 (SMP30) rescues cell death by enhancing plasma membrane Ca(2+)-pumping activity in Hep
T Fujita1, H Inoue, T Kitamura
1Department of Molecular Pathology, Tokyo Metropolitan Institute of Gerontology, Japan. tofujita@center.tmig.or.jp
Abstract:
Senescence marker protein-30 (SMP30) has been reported to decrease with aging in the rat liver. SMP30 has been also suggested to play a role as a Ca(2+)-binding protein localized in cytosol of hepatocytes. To elucidate the functional significance of SMP30, we have generated Hep G2 cell lines that stably express large amounts of SMP30 by transfection with human SMP30 cDNA. Using these cell lines, in view of the intracellular Ca2+ homeostasis, we then investigated cytosolic free Ca2+ concentration ([Ca2+]i) and Na(+)-independent Ca2+ efflux from the cells after extracellular ATP stimulation. Although stimulation of cells with ATP caused transient [Ca2+]i increase in both SMP30 and mock transfectants, rate of decrease after peak in [Ca2+]i was enhanced 2-fold by transfection of SMP30. Correspondingly, Ca2+ efflux was significantly increased in SMP30 transfectants compared with mock transfectants. In addition, more SMP30 transfectants survived than mock transfectants when cell death was induced by Ca2+ ionophore treatment. These results suggest that SMP30 regulates [Ca2+]i by modulating plasma membrane Ca(2+)-pumping activity, and thus down-regulation of SMP30 during aging may contribute to deterioration of cellular functions.
Insights
Senescence marker protein-30 (SMP30) regulates intracellular calcium levels by enhancing calcium efflux. Reduced SMP30 during aging may impair cellular function and contribute to age-related decline.
Area of Science:
- Cell Biology
- Biochemistry
- Gerontology
Background:
- Senescence marker protein-30 (SMP30) levels decrease with aging in rat liver.
- SMP30 is a calcium-binding protein found in hepatocyte cytosol.
- Its precise role in cellular calcium homeostasis and aging is not fully understood.
Purpose of the Study:
- To investigate the functional significance of SMP30 in intracellular calcium homeostasis.
- To determine if SMP30 influences calcium efflux and cellular response to calcium stress.
Main Methods:
- Generated Hep G2 cell lines with stable overexpression of human SMP30.
- Measured cytosolic free calcium concentration ([Ca2+]i) and Na(+)-independent Ca2+ efflux after ATP stimulation.
- Assessed cell survival following calcium ionophore treatment.
Main Results:
- SMP30 overexpression significantly enhanced the rate of cytosolic calcium decrease after ATP stimulation.
- Calcium efflux from SMP30-overexpressing cells was markedly increased compared to controls.
- Cells overexpressing SMP30 exhibited improved survival rates when subjected to calcium ionophore-induced cell death.
Conclusions:
- SMP30 plays a crucial role in regulating intracellular calcium ([Ca2+]i) by modulating plasma membrane calcium-pumping activity.
- The observed down-regulation of SMP30 during aging may contribute to cellular dysfunction and age-related decline.
- Targeting SMP30 could offer therapeutic potential for age-related cellular deterioration.