Growth hormone axis

Differentiated pituitary GH production, determined largely by POU1F1, is induced by GHRH and ghrelin and is suppressed by somatostatin by means of signaling through cognate somatotroph surface receptors. GH binds the preformed GHR dimer. Internal dimer rotation results in JAK2 phosphorylation (P) and signaling by JAK2-dependent and JAK2-independent pathways. GH targets include IGF-1, cell-proliferation factors, glucose metabolism, and cytoskeletal proteins. GHR internalization and translocation may directly induce nuclear proliferation genes^[1]. GHR signaling may be abrogated by suppressors of cytokine-signaling proteins and by phosphatases. GH production may be suppressed by a range of conditions^[2]. GH action targets pleiotropic tissues mainly in the organs depicted. A model of GH bound to the GHR dimer is shown.