The role of STAT proteins in growth hormone signaling

Growth hormone (GH) has long been known to be the body's primary regulator of body growth and a regulator of metabolism, yet the mechanisms by which G H regulates the transcription of specific genes required for these processe s are just now being delineated. GH binding to its receptor recruits and ac tivates the receptor-associated JAK2 that in turn phosphorylates tyrosines within itself and the GH receptor. These tyrosines form binding sites for a number of signaling proteins, including members of the family of signal tr ansducers and activators of transcription (STAT), Among the known signaling molecules for GH, STAT proteins play a particularly prominent role in the regulation of gene transcription. This paper will review what is currently understood about which STAT proteins are regulated by GH, how they are regu lated by GH, the GH-dependent genes they regulate, and discuss current theo ries about how GH-activated STAT signaling is regulated, Particular attenti on will be given to the novel role that STAT5 plays in sexually dimorphic g ene expression in the liver as determined by the secretory pattern of GH an d the role of STAT5 in body growth.