Demonstration of functional oxytocin receptors in human breast Hs578T cells and their up-regulation through a protein kinase C-dependent pathway

Oxytocin (OT) receptors (OTRs) have been demonstrated in a number of human breast tumors and tumor cells, but it was not clear whether the receptors w ere functional. We examined the regulation and function of OTR in a tumor c ell line, Hs578T, derived from human breast. These cells expressed moderate levels of OTR when cultured in 10% FBS, as demonstrated by RT-PCR and bind ing analyses. Serum deprivation resulted in the loss of OTRs, with no effec t on cell viability. Restoration of serum and addition of 1 mu M dexamethas one (DEX) increased OTR levels by about 9-fold. Up-regulation was blocked b y the addition of phospholipase C and PKC inhibitors. Serum/DEX; treatment also increased steady state OTR messenger RNA levels. OT increased intracel lular Ca2+ in a time- and dose-responsive manner, and the effects of OT wer e Lost when OTRs were downregulated by serum starvation. Serum/DEX up-regul ation of OTR restored the responsiveness to OT. OT also stimulated ERK-2 (e xtracellular signal-regulated protein kinase) phosphorylation and PGE(2) sy nthesis in Hs578T cells. In addition to showing that OTRs in the breast tum or cells are functional, these studies show that Hs578T cells can be used t o study molecular regulation of OTR gene expression and intracellular signa ling pathways stimulated by OT.