Intracellular free Ca2+ in the cell cycle in human fibroblasts: transitions between G1 and G0 and progression into S phase.
Intracellular free calcium ([Ca2+]i) has been proposed to play an important part in the regulation of the cell cycle. Although a number of studies have shown that stimulation of quiescent cells with growth factors causes an immediate rise in [Ca2+]i (Rabinovitch et al., 1986; Vincentini and Villereal, 1986; Hesketh et al., 1988; Tucker et al., 1989, Wahl et al., 1990), a causal relationship between the [Ca2+]i transient and the ability of the cells to reenter the cell cycle has not been firmly established. We have found that blocking the mitogen-induced elevation of [Ca2+]i with the cytoplasmic [Ca2+]i buffer dimethyl BAPTA (dmBAPTA) also blocks subsequent entry of cells into S phase. The dose response curves for inhibition of serum stimulation of [Ca2+]i and DNA synthesis by dmBAPTA are virtually identical including an anomalous stimulation observed at low levels of dmBAPTA. Reversal of the [Ca2+]i buffering effect of dmBAPTA by transient exposure of the cells to the Ca2+ ionophore ionomycin also reverses the inhibition of DNA synthesis 20-24 h later. Ionomycin by itself does not stimulate DNA synthesis. These data are consistent with the conclusion that a transient increase in [Ca2+]i occurring shortly after serum stimulation of quiescent fibroblasts is necessary but not sufficient for subsequent entry of the cells into S phase. This study is the first to show a direct relationship between early serum stimulated Cai2+ increase and subsequent DNA synthesis in human cells. It also goes beyond recent studies on BALB/3T3 cells by providing dose response data and demonstrating reversibility, which are strong indications of a cause and effect relationship.
Wahl
M
M
Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Ohio 45267-0524.
Gruenstein
E
E
D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D003470:Culture Media; D004247:DNA / Q000096:biosynthesis; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007399:Interphase / Q000187:drug effects / Q000502:physiology; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics
D002021:Buffers; D003470:Culture Media; D004533:Egtazic Acid; D004247:DNA; C058180:5,5'-dimethyl-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate; D002118:Calcium