Inositol 1,3,4,5-tetrakisphosphate stimulates the initiation of DNA synthesis in Ca2+-deprived rat liver cells

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Abstract
The G1-S boundary of non-neoplastic cells requires extracellular Ca2+ for successful transition. Inositol 1,3,4,5-tetrakisphosphate but not inositol 1,4,5-trisphosphate can partially replace Ca2+ and stimulate the initiation of DNA synthesis of Ca2+-deprived T51B rat liver cells but only if sufficient extracellular Ca2+ (i.e., 0.075 mM) is present. The potent tumor promoter and protein kinase C activator 12-O-tetradecanoylphorbol acetate is also capable of replacing ex-tracellular Ca2+ and partially stimulating the initiation of DNA synthesis. In addition, both inositol-1,3,4,5-tetrakisphosphate and 12-O-tetradecanoylphorbol acetate added together elicit a full DNA synthetic response.