Role of Gab2 and Shp2 in Hematopoietic Signalling

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DESCRIPTION (provided by applicant): Hematopoiesis is regulated by growth factors and cytokines, many of which signal via protein- tyrosine kinases (PTKs). Abnormal PTKs cause myeloproliferative disorders (MPD) and/or leukemia; e.g., leukemia-associated translocations that encode fusion-PTKs (e.g. Bcr/Abl, Tel-Jak2), or point mutations in PTKs, such as the V617F mutation in Jak2 found in many adult MPDs. Protein-tyrosine phosphatases (PTPs) also regulate tyrosyl phosphorylation. Their roles are less well understood, and until recently, PTP mutations had not been identified in MPD/leukemia. The long range goal of this research is to understand the function of the SH2-containing PTP Shp2 (PTPn11) and its binding protein, Gab2, in normal hematopoiesis and disease. Earlier work established that Shp2 in required for cytokine-evoked Ras/Erk pathway activation. More recently, mutations in Shp2, similar to "activated mutants" we generated earlier, were identified in human disease. Germ-line Shp2 mutations cause Noonan syndrome, (NS) an autosomal dominant disorder featuring developmental defects and increased risk of MPD, especially juvenile myelomonocytic leukemia (JMML). Somatic Shp2 mutations are found in JMML and other leukemias. JMML cases without Shp2 mutation have activated Ras or loss-of-function Nf1 mutations, consistent with Shp2's role in regulating Ras, but the biochemical and biological consequences of disease-associated Shp2 mutations was unclear. During the current funding period, we generated and characterized mouse models for NS and JMML. Our results suggested that leukemia-associated Shp2 mutants are strong hypermorphs that cause MPD by enhancing IL3/GMCSF signaling, whereas NS alleles are weaker hypermorphs. However, the extent to which the intrinsic properties of an Shp2 mutation determine disease phenotype, as opposed to genetic modifiers and/or cooperating alleles remains unclear. The target cell in which leukemogenic Shp2 acts remains unidentified, and the precise mechanism by which leukemogenic Shp2 mutants enhance IL3/GMCSF signaling remains unknown. In Preliminary Studies, we have developed a new, unique "knock-in" model for the leukemogenic mutant D61Y and an allelic series of other disease- associated Shp2 knock-in mutants. We will use these models to delineate the effect of leukemogenic and NS mutants, expressed under endogenous promoter control, on hematopoiesis and hematopoietic cell signaling, to identify the target cell(s) for Shp2-evoked MPD, and to assess the relative contribution of disease gene, modifier loci, and secondary events to MPD development. Very recent data indicate that leukemogenic Shp2 mutants act by enhancing Jak2 activation, suggesting a shared molecular pathway between childhood and adult MPD. We also will determine the mechanisms and consequences of Jak2 hyperactivation, and test whether Shp2 mutations may also play a role in adult MPD.