Abstract
We demonstrate here that p38 mitogen-activated protein (MAP) kinase is activated in response to cellular stimulation by human GH (hGH) in Chinese hamster ovary cells stably transfected with GH receptor cDNA. This activation requires the proline-rich box 1 region of the GH receptor required for JAK2 association and is prevented by pretreatment of cells with the JAK2-specific inhibitor AG490. ATF-2 is both phosphorylated and transcriptionally activated by hGH, and its transcriptional activation also requires the proline-rich box 1 region of the GH receptor. Expression of wild type JAK2 can further enhance hGH-induced ATF-2-, CHOP-, and Elk-1-mediated transcriptional activation, whereas pretreatment with AG490 is inhibitory. Use of either specific pharmacological inhibitors or transient transfection of cells with p38alpha MAP kinase cDNA or a dominant negative variant demonstrated that hGH-stimulated transcriptional activation of ATF-2 and CHOP, but not Elk-1, is regulated by p38 MAP kinase. Both the p38 MAP kinase and p44/42 MAP kinase are critical for hGH-stimulated mitogenesis, whereas only p38 MAP kinase is required for hGH-induced actin cytoskeletal re-organization. p38 MAP kinase is therefore an important regulator in coordinating the pleiotropic effects of GH.
Highlights
We demonstrate here that p38 mitogen-activated protein (MAP) kinase is activated in response to cellular stimulation by human Growth hormone (GH) in Chinese hamster ovary cells stably transfected with GH receptor cDNA
In order to determine whether cellular stimulation with human GH (hGH) results in the activation of p38 MAP kinase, we first examined whether hGH stimulation of cells resulted in the phosphorylation of p38 MAP kinase
Phosphorylated p38 MAP kinase was detected by use of a phospho-p38 MAP kinase (Thr-180/Tyr-182) antibody that detects p38 MAP kinase after dual phosphorylation at Thr-180 and Tyr-182. hGH stimulation of CHO-GHR1–638 cells resulted in increased p38 MAP kinase phosphorylation detectable 5 min after stimulation
Summary
We demonstrate here that p38 mitogen-activated protein (MAP) kinase is activated in response to cellular stimulation by human GH (hGH) in Chinese hamster ovary cells stably transfected with GH receptor cDNA. Use of either specific pharmacological inhibitors or transient transfection of cells with p38␣ MAP kinase cDNA or a dominant negative variant demonstrated that hGH-stimulated transcriptional activation of ATF-2 and CHOP, but not Elk-1, is regulated by p38 MAP kinase. We demonstrate here that hGH transiently phosphorylates and activates p38 MAP kinase in CHO cell lines stably transfected with rat GH receptor cDNA and that the activation of the p38 MAP kinase pathway by hGH is JAK2-dependent Both ATF-2 and CHOP (GADD153) are transcriptionally activated by hGH in a JAK2dependent manner, and p38 MAP kinase is required for both cytoskeletal re-organization and cell proliferation stimulated by hGH. The p38 MAP kinase pathway is an important regulator of the pleiotropic effects of GH
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