RAPID NUCLEAR ACTIONS OF GROWTH-HORMONE

The mechanisms by which growth hormone (GH) initiates its effect on gr owth are largely unknown. In this report we examine the acute actions of GH with a focus on the intracellular signaling pathways leading fro m the cell-surface GH receptor into the nucleus, and culminating in th e activation of specific target genes. We show that in vivo GH treatme nt leads to the rapid appearance of tyrosine-phosphorylated nuclear pr oteins and the equally rapid induction of c-fos and insulin-like growt h factor I gene transcription. A model is proposed for a GH-activated intracellular signal transduction pathway.