title: Growth hormone pulse-activated STAT5 signalling: a unique regulatory mechanism governing sexual dimorphism of liver gene expression.
abstract: Growth hormone (GH) exerts sexually dimorphic effects on liver gene transcription that are regulated by the temporal pattern of pituitary GH release; this release is intermittent in male rats and nearly continuous in females. Comparisons of liver nuclear protein tyrosine phosphorylation in male and female rats have led to the discovery that the liver transcription factor STAT5b is tyrosine phosphorylated in male but not female rats in response to GH pulses. Intermittent plasma GH pulses trigger a rapid and repeated tyrosine phosphorylation and nuclear translocation of liver STAT5b in intact male rats, while the more continuous pattern of GH exposure down-regulates the STAT5b signalling pathway in female rat liver. The central importance of STAT5b for the physiological effects of GH pulses has been verified using a mouse gene knockout model. STAT5b gene disruption leads to a major loss of multiple sexually differentiated responses associated with the sexually dimorphic pattern of pituitary GH secretion. Male-characteristic body growth rates and male-specific liver gene expression are decreased to wild-type female levels in STAT5b-/- males, while female-predominant liver gene products are increased in males to near female levels. STAT5b is thus a liver-expressed, latent cytoplasmic transcription factor that undergoes repeated tyrosine phosphorylation and nuclear translocation in response to intermittent plasma GH stimulation, and is a key intracellular mediator of the stimulatory effects of GH pulses on male-specific liver gene transcription. Other studies indicate, however, that STAT5a and STAT5b are both required for constitutive expression in female, but not male liver, of certain GH-regulated CYP enzymes. GH activation of both STAT5 proteins, which in turn form distinct homodimeric and heterodimeric DNA-binding complexes, is thus an important determinant of the sex-dependent and gene-specific effects that GH has on the liver.
authors.affiliation: Department of Biology, Boston University, MA 02215, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Waxman
mesh_terms: D000818:Animals; D018929:Cell Culture Techniques; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D013006:Growth Hormone / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D008099:Liver / Q000378:metabolism; D051379:Mice; D008894:Milk Proteins; D008954:Models, Biological; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
chemical_list: D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; C494095:STAT5B protein, human; C494093:Stat5a protein, mouse; C494094:Stat5a protein, rat; C494096:Stat5b protein, mouse; C494097:Stat5b protein, rat; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; D013006:Growth Hormone; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; C507927:Jak2 protein, rat; D053614:Janus Kinase 2; C516724:PTPN11 protein, human; C509249:PTPN6 protein, human; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C516725:Ptpn11 protein, mouse; C516727:Ptpn11 protein, rat; C509248:Ptpn6 protein, mouse; C509250:Ptpn6 protein, rat