Growth hormone and cell growth.

Growth hormone (GH) promotes stem cell activation, cell proliferation, differentiation and survival, either directly or through the induction of IGF-1. GH acts via its cell membrane receptor to initiate a range of signalling pathways, with JAK2 kinase activation of STAT5 being the most important. The transcription factor STAT5 acts to induce expression of the key growth mediator, IGF-1, but also regulates the expression of a host of other genes, some of which are important growth regulators. In addition to its signalling from the cell membrane, the GH receptor translocates to the nucleus in a GH-dependent manner, where it regulates the expression of other cell growth-related genes, and sensitises the cell to the proliferative action of GH.