p19Arf Cooperates with Shp2 in Lymphoid Leukemogenesis

Shp2 gain-of-function mutations are found in human acute lymphoblastic leukemia, as well as in juvenile myelomonocytic leukemia and acute myeloid leukemias. Genetic data from Noonan Syndrome patients bearing mutations in PTPN11/Shp2 suggest that Shp2 mutation alone is insufficient for leukemogenesis, and other genetic alterations are required. We investigated E76K Shp2-induced leukemogenesis in p19Arf+/− and p19Arf−/− backgrounds. Wild type mice reconstituted with Arf+/− or Arf−/− bone marrow cells (BMCs) transduced with E76K Shp2 developed hematologic disease with increased incidence and severity than mice reconstituted with vector-transduced Arf+/− or Arf−/− BMCs, with E76K Shp2-transduced Arf−/− BMCs causing the most aggressive disease at the highest rate. E76K Shp2 expression in Arf+/− BMCs caused myeloproliferation consisting of mainly Mac1+Gr1+ cells associated with extramedullary hematopoiesis, but E76K Shp2 expression in Arf−/− BMCs caused a shift in disease phenotype to transplantable B220+ leukemias. Consistently, E76K Shp2 transduced Arf+/− or Arf−/− BMCs from reconstituted pre-leukemic mice showed increased proB cell populations compared to vector transduced BMCs, suggesting that the E76K Shp2 expressing proB cells are the leukemia precursors. While Shp2 is well known to confer GM-CSF hypersensitivity in methylcellulose cultures, we found that E76K Shp2 transduced BMCs were also hypersensitive to the lymphoid colony-stimulating factor IL-7, and E76K Shp2 expressing lymphoid BMCs formed colonies in the absence of exogenous growth factor. These data suggest that gain-of-function Shp2 confers transformation features to B cell precursors and that Arf deletion potentiates E76K Shp2 in lymphoid leukemogenesis.