The effects of autocrine human growth hormone (hGH) on human mammary carcinoma cell behavior are mediated via the hGH receptor

The human GH (hGH) antagonist B2036 combines a single amino acid substituti on impairing receptor binding site 2 (G120K) with eight additional amino ac id substitutions that improve binding site 1 affinity. B2036 does not bind, activate, or antagonize the human PRL receptor and therefore is suitable t o determine cellular effects mediated specifically through the hGH receptor . We have used this hGH receptor specific antagonist in MCF-7 cells stably transfected with either the hGH gene (MCF-hGH) or a translation deficient h GH gene (MCF-MUT) to determine whether the effects of autocrine hGH on mamm ary carcinoma cell behavior are mediated via the hGH receptor. Enhanced JAX 2 tyrosine phosphorylation observed in MCF-hGH cells compared with MCF-MUT cells is abrogated by B2036 as is the autocrine hGH stimulated increase in total cell number and DNA synthesis. Interestingly, autocrine hGH functions as a potent inhibitor of apoptosis induced by serum withdrawal compared wi th exogenously added hGH, and the protection against apoptosis afforded by autocrine hGH is abrogated by B2036. B2036 also inhibited autocrine hGH sti mulated transcriptional activation mediated by either STAT5, CHOP (p38 MAP kinase specific) or Elk-1 (p44/42 MAP kinase specific). Finally, B2036 inhi bited the autocrine hGH-dependent enhancement of the rate of mammary carcin oma cell spreading on a collagen matrix. Thus, the effects of autocrine hGH on human mammary carcinoma cell behavior are mediated via the hGH receptor .