FUNCTIONAL EXPRESSION OF A MOUSE GROWTH-HORMONE RECEPTOR CDNA IN TRANSFECTED MOUSE L-CELLS

A cDNA encoding a full-length mouse (m) growth hormone receptor (GHR) derived from 3T3 F442A cells was amplified by RT-PCR and cloned into a mammalian expression vector. A mouse L cell:line (mGHR1.6), which exp resses high levels of full-length mGHR, was established. A mGHR-specif ic mRNA of approx 2.8 kb was found in these cells. Ligand binding stud ies showed that mGHR 1.6 cells were capable of binding I-125-hGH With a dissociation constant (K-d) of 2.9 +/- 0.13 nM. Scatchard analysis i ndicated that mGHR1.6 cells had only a single class of mGHR and posses sed approx 128,000 GH specific binding sites per cell. Affinity crossl inking studies showed that the recombinant mGHR possessed an apparent molecular mass of 105 kDa. In addition, mGHR1.6 cells responded to gro wth hormones (GHs) from several species. Two proteins, pp92 and pp95, were found to be tyrosyl phosphorylated following GH treatment. An hGH antagonist, hGH-G120R, inhibited GH-induced phosphorylation of both p p92 and pp95 in a dose-dependent manner. This cell line may be used as an in vitro model in the studies of GH signal transduction and in the screening of GH analogs for biological activity.