Differential activation of Stat3 and Stat5 by distinct regions of the growth hormone receptor.

Abstract

The GH receptor (GHR) is a member of the cytokine receptor superfamily; its signaling involves the activation of Janus tyrosine kinases (JAK2) and Stat (signal transducers and activators of transcription) transcription factors. Using truncated and tyrosine mutants of the receptor, we show that different receptor domains are essential for the activation of Stat3 and Stat5. GH-dependent phosphorylation of JAK2, Stat3, and Stat5, as well as transactivation studies with reporter genes containing Stat3 and Stat5 DNA-binding elements, was performed in cells expressing the various GHR mutants. The membrane-proximal region of the receptor necessary for JAK2 activation is sufficient for Stat3 activation. In contrast, C-terminal tyrosine residues of GHR are absolutely required for Stat5 activation. The same residues are also involved in the regulation of JAK2 dephosphorylation, possibly through the activation of a phosphatase. Using in vitro experiments with glutathione-S-transferase fusion proteins, we demonstrate that the SH2 domain of Stat5 binds to the carboxy-terminal tyrosine-phosphorylated residues of GHR. Our results show that a cytokine receptor can mediate differently the activation of distinct Stat proteins that could be involved in cytokine-specific effects.

The role of STAT proteins in growth hormone signaling

“…However, signi®cantly truncated forms of GH receptor which lack most or all phosphorylated tyrosines can mediate GH-induced tyrosyl phosphorylation of STATs 1 and 3 and binding of STATs 1 and 3 to the Sis inducible element (SIE) of c-fos. This suggests that speci®c phosphorylated tyrosines in GH receptor may not be essential for activation of STATs 1 and 3 by GH (Smit et al, 1996;Sotiropoulos et al, 1995Sotiropoulos et al, , 1996Yi et al, 1996). While not essential for GHdependent activation of STATs 1 and 3, phosphorylated tyrosine(s) in the N-terminal half of the cytoplasmic domain of the rat GH receptor may contribute to maximal activation of STATs 1 and 3 in response to GH (Smit et al, 1996).…”

“…GH induces the binding of STAT5 proteins to IFNg activated sequence (GAS)-like elements (GLE) in several dierent genes, including the GH-sensitive spi 2.1, Insulin 1 and p450 CYP3A 6 beta-hydroxylase genes (Bergad et al, 1995;Galsgaard et al, 1996;Hansen et al, 1996;Subramanian et al, 1995;. STAT5 mediates GH-dependent transcriptional activation of promoter-reporter constructs containing the STAT5-binding promoter elements of these genes (Bergad et al, 1995;Galsgaard et al, 1996;Hansen et al, 1996;Sotiropoulos et al, 1996;Subramanian et al, 1995;Wood et al, 1995).…”

A common polymorphism of the growth hormone receptor is associated with increased responsiveness to growth hormone

“…We transiently cotransfected 293 HEK fibroblasts with vectors expressing full-length GHR, d3-GHR or both using the LHRE-luciferase reporter plasmid, which is activated by full-length GHR 2,11 . When cells were exposed to various growth hormone concentrations, d3-GHR induced a higher transcriptional activity of the reporter construct than full-length GHR (Fig.…”

Growth Hormone Regulates Phosphorylation and Function of CCAAT/Enhancer-binding Protein β by Modulating Akt and Glycogen Synthase Kinase-3

“…Regulation of the expression of the proto-oncogene c-fos has served as a useful model for studying regulation of gene expression by GH (5,6), and has demonstrated diverse effects of GH on the phosphorylation of transcription factors. For example, GHstimulated tyrosine phosphorylation of STATs and serine phosphorylation of Elk-1 are required for these transcription factors to activate transcription of c-fos in response to GH (7)(8)(9)(10)(11)(12)(13).…”