Increased SH2-Bbeta content and membrane association in transgenic mice overexpressing GH.
Transgenic mice overexpressing GH present a marked GH signaling desensitization, reflected by low basal phosphorylation levels of the tyrosine kinase JAK2, and signal transducer and activator of transcription-5 (STAT5) and a lack of response of these proteins to a high GH dose. To evaluate the mechanisms involved in the regulation of JAK2 activity by high GH levels in vivo, the content and subcellular distribution of SH2-Bbeta were studied in GH-overexpressing transgenic mice. SH2-B is a member of a conserved family of adapter proteins characterized by the presence of a C-terminal SH2 domain, a central pleckstrin homology (PH) domain, and an N-terminal proline rich region. The isoform SH2-Bbeta modulates JAK2 activity by binding to the phosphorylated enzyme, further increasing its activity. However, it may also interact with non-phosphorylated inactive JAK2 via lower affinity binding sites, preventing abnormal activation of the kinase. SH2-Bbeta may also function as an adapter protein, acting as a GH signaling mediator. We now report that, in an animal model of GH excess in which JAK2 is not phosphorylated, although it is increased in the membrane-fraction, both the level of SH2-Bbeta, and especially its association to membranes, are augmented (67% and 13-fold vs normal mice values respectively), suggesting SH2-Bbeta could modulate JAK2 activity in vivo.
Miquet
J G
JG
Instituto de Química y Fisicoquímica Biológicas (UBA-CONICET), Facultad de Farmacia y Bioquímica, Junín 956 (1113) Buenos Aires, Argentina.
Sotelo
A I
AI
Bartke
A
A
Turyn
D
D
D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis* / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D004268:DNA-Binding Proteins / Q000032:analysis / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D013006:Growth Hormone / Q000235:genetics / Q000378:metabolism*; D047468:Immunoprecipitation; D007425:Intracellular Membranes / Q000378:metabolism; D053614:Janus Kinase 2; D051379:Mice; D008822:Mice, Transgenic; D008862:Microsomes, Liver / Q000378:metabolism*; D008894:Milk Proteins / Q000032:analysis / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000032:analysis* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000032:analysis* / Q000378:metabolism; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000032:analysis / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D050799:STAT5 Transcription Factor; C115327:Sh2bpsm1 protein, mouse; D015534:Trans-Activators; D013006:Growth Hormone; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2