Involvement of JAK2 and Src kinase tyrosine phosphorylation in human growth hormone-stimulated increases in cytosolic free Ca2+ and insulin secretion

1 Karolinska Institute, Department of Internal Medicine, Stockholm South Hospital, Stockholm and 2 Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden Submitted 18 August 2005 ; accepted in final form 31 March 2006 We previously reported that human growth hormone (hGH) increases cytoplasmic Ca 2+ concentration ([Ca 2+ ] i ) and proliferation in pancreatic -cells (Sjöholm Å, Zhang Q, Welsh N, Hansson A, Larsson O, Tally M, and Berggren PO. J Biol Chem 275: 21033–21040, 2000) and that the hGH-induced rise in [Ca 2+ ] i involves Ca 2+ -induced Ca 2+ release facilitated by tyrosine phosphorylation of ryanodine receptors (Zhang Q, Kohler M, Yang SN, Zhang F, Larsson O, and Berggren PO. Mol Endocrinol 18: 1658–1669, 2004). Here we investigated the tyrosine kinases that convey the hGH-induced rise in [Ca 2+ ] i and insulin release in BRIN-BD11 -cells. hGH caused tyrosine phosphorylation of Janus kinase (JAK)2 and c-Src, events inhibited by the JAK2 inhibitor AG490 or the Src kinase inhibitor PP2. Although hGH-stimulated rises in [Ca 2+ ] i and insulin secretion were completely abolished by AG490 and JAK2 inhibitor II, the inhibitors had no effect on insulin secretion stimulated by a high K + concentration. Similarly, Src kinase inhibitor-1 and PP2, but not its inactive analog PP3, suppressed [Ca 2+ ] i elevation and completely abolished insulin secretion stimulated by hGH but did not affect responses to K + . Ovine prolactin increased [Ca 2+ ] i and insulin secretion to a similar extent as hGH, effects prevented by the JAK2 and Src kinase inhibitors. In contrast, bovine GH evoked a rise in [Ca 2+ ] i but did not stimulate insulin secretion. Neither JAK2 nor Src kinase inhibitors influenced the effect of bovine GH on [Ca 2+ ] i . Our study indicates that hGH stimulates rise in [Ca 2+ ] i and insulin secretion mainly through activation of the prolactin receptor and JAK2 and Src kinases in rat insulin-secreting cells. c-Src; growth hormone receptor; prolactin receptor; Ca 2+ -induced Ca 2+ release Address for reprint requests and other correspondence: Q. Zhang, Research Ctr., Karolinska Inst., Stockholm South Hospital, SE-11883 Stockholm, Sweden (e-mail: qimin.zhang{at}sos.ki.se )