Growth hormone action in rat insulinoma cells expressing truncated growth hormone receptors

Annette Møldrup, G Allevato, Thomas Dyrberg, N Billestrup, Jens Høiriis Nielsen

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Abstract

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.
Original languageEnglish
JournalThe Journal of Biological Chemistry
Volume266
Issue number26
Pages (from-to)17441-5
Number of pages5
ISSN0021-9258
Publication statusPublished - 15 Sep 1991

Keywords

  • Animals
  • Cytoplasm
  • Growth Hormone
  • Insulinoma
  • Kinetics
  • Mutagenesis, Site-Directed
  • Precipitin Tests
  • Rats
  • Receptors, Somatotropin
  • Transfection
  • Tumor Cells, Cultured

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