GH signalling in pancreatic beta-cells.
GH and its related peptide PRL are known to stimulate proliferation and insulin biosynthesis in pancreatic beta-cells, and assumed to be involved in their functional maturation. We investigated signal transduction of GH and PRL in insulin-secreting cells using the differentiated rat insulinoma cell line, INS-1. In these cells, both hormones stimulated proliferation and DNA synthesis, increased viability, cellular metabolism and insulin content. GH induced cytosolic Ca2+ ([Ca2+]i) rises, which appear to be due to Ca2+-influx through voltage-gated Ca2+-channels. GH also promoted tyrosine phosphorylation of several proteins in INS-1 cells, one of which was identified as JAK2 tyrosine kinase. Moreover, GH caused changes in DNA binding of nuclear proteins to some interferon-gamma-activated sites. Verapamil inhibited neither DNA synthesis nor JAK2 phosphorylation stimulated by GH, whereas a tyrosine kinase inhibitor, lavendustin A, blocked the mitogenic effect. Involvement of cAMP is also suggested because Rp-cAMPS, a competitive inhibitor of protein kinase A, abolished both [Ca2+]i rises and DNA synthesis stimulated by GH. The effects of GH and PRL on [Ca2+]i, JAK2 phosphorylation and DNA binding of the STATs were virtually identical in INS-1 cells. Since both hormones failed to activate MAP kinase in these cells, it is strongly suggested that activation of the JAK-STAT pathway is the major signalling event for the mitogenic effects of GH and PRL in beta-cells. It remains to be clarified whether the [Ca2+]i rise mediates other effects of these hormones.
Sekine
N
N
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Wollheim
C B
CB
Fujita
T
T
D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D019382:Human Growth Hormone / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011388:Prolactin / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D015533:Transcriptional Activation
D007328:Insulin; D019382:Human Growth Hormone; D011388:Prolactin; D011505:Protein-Tyrosine Kinases; D002118:Calcium