Extracellular calcium stimulates DNA synthesis in synergism with zinc, insulin and insulin-like growth factor I in fibroblasts

In serum-starved mouse NIH 3T3 fibroblasts cultured in 1.8 mM Ca2+-containi ng medium, addition of 0.75-2 mM extra Ca2+ stimulated DNA synthesis in syn ergism with zinc (15-60 mu M), insulin and insulin-like growth factor I. Ex tra Ca2+ stimulated phosphorylation/activation of p42/p44 mitogen-activated protein kinases by an initially (10 min) zinc-independent mechanism; howev er, insulin, and particularly zinc, significantly prolonged Ca2+-induced mi togen-activated protein kinase phosphorylation. Ln addition, extra Ca2+ act ivated p70 S6 kinase by a zinc-dependent mechanism and enhanced the stimula tory effect of zinc on choline kinase activity. Insulin and insulin-like gr owth factor I also commonly increased both p70 S6 kinase and choline kinase activities. In support of the role of the choline kinase product phosphoch oline in the mediation of mitogenic Ca2+ effects, cotreatments with the cho line kinase substrate choline (250 mu M) and the choline kinase inhibitor h emicholinium-3 (2 mM) enhanced and inhibited, respectively, the combined st imulatory effect of extra Ca2+ (3.8 mM total) and zinc on DNA synthesis. In various human skin fibroblast lines, 1-2 mM extra Ca2+ also stimulated DNA synthesis in synergism with zinc and insulin. The results show that in var ious fibroblast cultures, high concentrations of extracellular Ca2+ can col laborate with zinc and certain growth factors to stimulate DNA synthesis. C onsidering the high concentration of extracellular Ca2+ in the dermal layer , Ca2+ may promote fibroblast growth during wound healing in concert with z inc, insulin growth factor-I insulin, and perhaps other growth factors.