GROWTH-HORMONE (GH) INDUCES TYROSINE-PHOSPHORYLATED PROTEINS IN MOUSEL-CELLS THAT EXPRESS RECOMBINANT GH RECEPTORS

Porcine and bovine GH receptor (GHR) cDNAs were stably expressed in mo use L cells, which normally do not possess detectable levels of mouse GHR. Expression of the GHR cDNAs resulted in specific binding of I-125 -labeled GH by these cell lines. To study GHR-related signaling events in these cells, protein tyrosine phosphorylation was examined. In GH- treated cells, a tyrosine-phosphorylated protein with a molecular mass of approximate to 95 kDa (pp95) was increased dramatically (approxima te to 100-fold) relative to non-GH-treated cells. The amount of pp95 w ithin the cells after GH treatment was positively correlated with the number of GHRs on the cells. Tyrosine phosphorylation of pp95 could no t be induced by prolactin, insulin, insulin-like growth factor I, inte rleukin 2, epidermal growth factor, platelet-derived growth factor, or fibroblast growth factor. Phosphorylation of pp95 was found to be a r apid event that could be observed 60 sec after GH treatment, Also, pp9 5 appears to exist as a complex of two proteins, i.e., pp95 and pp96. The GH-induced response by these cells may be of use in screening GH a nalogs for biological activity.