Potentiation of Calcium‐Mediated Stimulation of DNA Synthesis by Ethanol in Human and Mouse Fibroblasts

Abstract

Alcohol abuse is a risk factor for cancers of the gastrointestinal tract, and it also can precipitate psoriasis characterized by hyperproliferation of epidermal cells. Because these effects of alcohol may involve stimulation of cell growth, and ethanol (EtOH) was shown to enhance DNA synthesis in mouse fibroblasts and epidermal cells, we conducted a study to determine whether EtOH can also stimulate mitogenesis in human fibroblasts and keratinocytes. In keratinocytes, EtOH had no effects on mitogenesis after shorter (17-hr) treatments, but it partially prevented inhibition of DNA synthesis elicited by longer treatments (3-4 days) with 2 mM calcium (Ca2+), a differentiation-inducing agent. In contrast, treatment of serum-starved zinc-treated (40 microM) human skin fibroblasts with 50-60 mM EtOH for 17 hr resulted in increased DNA synthesis. EtOH-induced DNA synthesis was blocked by 1 mM EGTA, a specific Ca2+ chelator. Despite the presence of 1.8 mM Ca2+ in the cell culture medium, the addition of 1 mM extra Ca2+ (final concentration, 2.8 mM) for 17 hr induced DNA synthesis, presumably mediated by Ca2+ receptors. In eight independent human skin fibroblast lines examined, treatment with EtOH for 46 hr, but not for 17 hr, invariably enhanced the effects of Ca2+ on DNA synthesis, consistent with synergistic stimulation of cell proliferation by EtOH and Ca2+. Neomycin, a Ca2+ receptor agonist, and EtOH also exerted synergistic effects on DNA synthesis after longer (46-hr) treatments. In mouse NIH 3T3 fibroblasts, both EtOH- and Ca2+-enhanced DNA synthesis after 17-hr treatment, but they stimulated cell proliferation only in combination. The results indicate that in human fibroblasts, EtOH can potentiate the longer-term effects of high concentrations of Ca2+ on DNA synthesis whereas, in keratinocytes, EtOH may inhibit Ca2+-induced differentiation.