Regulation of growth hormone signaling by SIRP(alpha) and the protein tyrosine phosphatase SHP-2.

Reversible tyrosyl phosphorylation of proteins is a key regulatory mechanism that cells utilize to transduce signals in response to a variety of polypeptide hormones and growth factors, which regulate cellular growth, movement, or metabolism. Growth hormone (GH) is a key regulator of body growth and metabolism, and GH exerts its physiological actions by binding to GH receptor (GHR) and rapidly and transiently inducing tyrosyl phosphorylation and activation of the Janus tyrosine kinase JAK2. Activation of JAK2 is required for tyrosyl phosphorylation and/or activation of signaling molecules such as GHR, JAK2, the signal transducer and activator of transcription STAT5B and extracellular signal regulated kinases ERKs 1 and 2. Although the events which initiate GH signaling (such as JAK2 activation and tyrosyl phosphorylation) are beginning to be understood, the events which terminate GH signaling (such as dephosphorylation of signaling proteins) are poorly understood. In this dissertation, the protein tyrosine phosphatase SHP-2 and its substrate SIRP a (signal regulatory protein a ) are identified as negative regulators of GH signaling. GH induces tyrosyl phosphorylation of SHP-2 and SIRP a and association of SHP-2 with both SIRP a and GHR. Although JAK2 can associate with and tyrosyl phosphorylate SIRP a in a COS cell overexpression system, neither LiF nor IFN g , ligands that activate JAK2, induces tyrosyl phosphorylation of SIRP a or association of SHP-2 with SIRP a . Overexpression of wild-type SIRP a , but not SIRP a which lacks all potential SHP-2 binding sites, reduces tyrosyl phosphorylation of STAT5B, ERK, and a subset of JAK2 associated with SIRP a . To explore further the role of SHP-2 in GH signaling, the role of the association of SHP-2 with GHR was examined. SHP-2 associates with tyrosine 595 of GHR via the SH2 domains of SHP2, and mutation of tyrosine 595 prolongs GH-promoted tyrosyl phosphorylation of STAT5B and GHR, but not JAK2. These data indicate that SHP-2 and SIRP a may negatively regulate GH signal transduction.PhDBiological SciencesMicrobiologyMolecular biologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131798/2/9929962.pd