Activating Shp2 Mutations Cause Progressive Myeloproliferative Disorder in Mice.

Mutations in the SH2-containing tyrosine phosphatase, Shp2 (PTPN11) have been found in human diseases. Germ-line Shp2 mutations cause ~50% of Noonan Syndrome (NS), which is associated with an increased risk of juvenile myelomonocytic leukemia (JMML). Somatic Shp2 mutations are found in ~35% of sporadic JMML, most other cases have either activating Ras mutations or homozygous Nf1 deficiency. Shp2 mutations are also found at lower incidence in acute myeloid leukemia (AML), myelodysplastic syndrome (MDS) and B-cell acute lymphoblastic leukemia (B-ALL). NS and leukemia-associated Shp2 mutations often affect the same residue, but result in different substitution. We previously showed that leukemia-associated mutants E76K or D61Y, but not wild type (WT) Shp2 could transform bone marrow (BM) or fetal liver cells and give rise to cytokine-independent myeloid colony formation. Transplantation of E76K- or D61Y- (but not parental virus or WT Shp2) transduced BM evoked invasive MPD in most recipients and majority of them died at 6–7 months. We have generated knock-in mice for the Shp2 mutants D61G and D61Y to better understand the effects of these mutations under endogenous promoter control. Whereas D61G is associated with both NS and leukemia, D61Y is only found in leukemia and catalytically more active than D61G in basal state. D61G/+ mice exhibited all major features of NS and a mild, well-tolerated MPD for ~1 year and then progressed to fatal MPD. Constitutive expression of the D61Y heterozygous allele was embryonic lethal. However, when an inducible allele of D61Y (inD61Y) was crossed to Mx-Cre mice and expressed upon pI-pC induction, these mice rapidly developed MPD and ~50% mice died within a period of 4–7 months. Immunophenotypic analysis of bone marrow and spleen of these mice showed marked expansion of Gr-1/Mac-1 positive population indicating that these mice died of infiltrating MPD. Bone marrow macrophages from D61G/+ and inD61Y mice showed increased GM-CSF-evoked proliferation and increased overall tyrosine phosphorylation. Likewise GM-CSF-evoked activation of Erk, Akt, Jak2 and Stat5 were enhanced, as was Ras loading suggesting that leukemogenic Shp2 causes MPD by enhancing both Ras/Erk and Jak2/Stat5 pathways. The results of our retroviral and knock-in models suggest that leukemia-associated Shp2 mutant is sufficient to initiate myeloid leukemogenesis in mice.