Growth hormone action in rat insulinoma cells expressing truncated growth hormone receptors.
Transfection of the insulin-producing rat islet tumor cell line RIN-5AH with a full length cDNA of the rat hepatic growth hormone (GH) receptor (GH-R1-638) augments the GH-responsive insulin synthesis in these cells. Using this functional system we analyzed the effect of COOH-terminal truncation of the GH receptor. Two mutated cDNAs encoding truncated GH receptors, GH-R1-294 and GH-R1-454, respectively, were generated by site-directed mutagenesis and transfected into the RIN cells. Both receptor mutants were expressed on the cell surface and displayed normal GH binding affinity. Whereas GH-R1-638 had a molecular mass of about 110 kDa, GH-R1-294 and GH-R1-454 showed molecular masses of 49 and 80 kDa, respectively. Cells expressing GH-R1-454 internalized GH to a similar extent as cells transfected with the full length receptor and the parent cell line, but GH-R1-294-expressing cells showed a markedly reduced capability of GH internalization. In contrast to cells transfected with GH-R1-638, none of the cell lines expressing truncated GH receptors exhibited any increase of the GH-stimulated insulin production. We conclude that domains within the COOH-terminal half of the cytoplasmic part of the GH receptor are required for transduction of the signal for GH-stimulated insulin synthesis, whereas cytoplasmic domains proximal to the transmembrane region are involved in receptor-mediated GH internalization.
Møldrup
A
A
Hagedorn Research Laboratory, Gentofte, Denmark.
Allevato
G
G
Dyrberg
T
T
Nielsen
J H
JH
Billestrup
N
N
D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology*; D007340:Insulinoma / Q000378:metabolism; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D011233:Precipitin Tests; D051381:Rats; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D011986:Receptors, Somatotropin; D013006:Growth Hormone