Dexamethasone does not interfere with hormone-sensitive PI hydrolysis

Serum, but not epidermal growth factor (EGF), stimulated the release of radiolabeled inositol phosphates from human embryo palate mesenchyme (HEPM) cells prelabeled with [3H]-myoinositol. Pretreatment of cells with 10(-6) M dexamethasone (DEX) for 48 h had no effect on the release of inositol phosphates in response to serum. Furthermore, although treatment of the glucocorticoid-sensitive A/J strain of mouse embryo palate mesenchyme (MEPM) cells with 10(-6) M DEX inhibited their proliferation by 40%, it had no effect on the activity of phospholipase(s) C. However, DEX did enhance the incorporation of [3H]-myoinositol into membrane lipids. We interpret these data to mean that 1) serum factors enhance metabolism of inositol lipids in HEPM cells, 2) DEX does not interfere with the primary events by which agonists utilize metabolism of inositol lipids as a mechanism for transmembrane signaling, and 3) DEX may affect synthesis of phosphoinositides, as reported by Grove et al. (Biochem. Biophys. Res. Commun. 110:200-207, 1983; J. Craniofac. Genet. Dev. Biol. Suppl. 2:285-292, 1986).