A growth hormone (GH) analog can antagonize the ability of native GH to promote differentiation of 3T3-F442A preadipocytes and stimulate insulin-like and lipolytic activities in primary rat adipocytes.
The effect of amino acid substitutions introduced to the third alpha-helix in bovine GH (bGH) was investigated. A GH analog (bGH-M8), in which three amino acids were substituted to form an idealized amphiphilic alpha-helix, possessed the same specific binding affinity as wild-type bGH to cell membranes prepared from 3T3-F442A cells or rat adipocytes. However, bGH-M8 failed to stimulate preadipocyte differentiation, as measured by the level of glycerol-3-phosphate dehydrogenase activity. An equimolar concentration of bGH-M8 was inhibitory for this adipogenic effect caused by bGH at a concentration of 30 pM. bGH-M8 also failed to induce an insulin-like response and reduced lipolytic potency in rat primary adipocytes. A 10-fold excess of bGH-M8 abolished the effect of wild-type bGH in the insulin-like and lipolytic assays. Thus, bGH-M8 inhibited these actions of wild-type bGH and, therefore, appears to be a competitive antagonist. These results suggest that a major biologically active domain resides in the third alpha-helix of bGH, which is independent of amino acids important in the initial interaction of GH with its receptor.
Okada
S
S
Department of Zoological and Biomedical Sciences, Ohio University, Athens 45701.
Chen
W Y
WY
Wiehl
P
P
Kelder
B
B
Goodman
H M
HM
Guller
S
S
Sonenberg
M
M
Kopchick
J J
JJ
D016475:3T3 Cells; D000273:Adipose Tissue / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D013006:Growth Hormone / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors*; D007328:Insulin / Q000494:pharmacology*; D008066:Lipolysis / Q000187:drug effects*; D008297:Male; D051379:Mice; D051381:Rats
D007328:Insulin; D013006:Growth Hormone