IN-VITRO AND IN-VIVO STUDIES OF ANTAGONISTIC EFFECTS OF HUMAN GROWTH-HORMONE ANALOGS

A bovine growth hormone (bGH) analog, bGH-G119R, has been shown to act as a functional antagonist of GH activity both in vitro and in vivo. In the present study, human (h) GH analogs with alterations in the thi rd alpha-helix (G120A, G120R) and N terminus (I4A) were generated. The se two regions have been reported to form binding site 2 in hGH, which is involved in in vitro dimerization of the GH receptor (GHR). The bi ological activities of these hGH analogs were tested in vitro by a rad ioreceptor assay and an assay to test the ability of the molecules to induce tyrosine phosphorylation of a 93-kDa protein in a human lymphoc yte line, IM-9. The growth rate of transgenic mice that express differ ent hGH analogs was used as an in vivo test of the activity of the mol ecules. The results demonstrated that G120R is a potent hGH antagonist both in vitro and in vivo. Transgenic mice expressing G120R demonstra ted a growth-suppressed phenotype. However, I4A, which has been demons trated to be a potent inhibitor of in vitro GHR dimerization, exhibite d full growth promoting activity in transgenic mice. Thus, the ability of hGH analogs to induce GHR dimerization in vitro and the ability to promote growth in vivo are not directly correlated.