Dok1 and SHIP act as negative regulators of v-Abl-induced pre-B cell transformation, proliferation and Ras/Erk activation

The v-Abl tyrosine kinase activates several signaling pathways during transformation of bone marrow cells in mice. Because the SH2-containing inositol 5′-phosphatase (SHIP) and Downstream of tyrosine kinase 1 (Dok1) have been shown to interact with Abl, the effect of SHIP and Dok1 deficiency on v-Abl transformation was investigated. Bone marrow cells from either Dok1- or SHIP-deficient mice are more susceptible to transformation by v-Abl. v-Abl-transformed preB cells from these knockout mice show Abl kinase-dependent hyperproliferation and moderate resistance to apoptosis. Elevated activation of Ras, Raf-1, and Erk, but not of Akt, was observed in either SHIP^-/- or Dok1^-/- v-Abl-transformed cells. This activation is sensitive to treatment with STI571. Furthermore, treatment of these cells with either a farnesyltransferase inhibitor or a MEK1/2 inhibitor abrogates the increased proliferation of SHIP^-/- or Dok1^-/- cells in a dose-dependent manner. Complementation of SHIP^-/- or Dok1 ^-/- cells abrogates their hyperproliferation and intracellular Erk activation. These data indicate that both SHIP and Dok1 functionally regulate the activation of Ras-Erk pathway by v-Abl and affect the mitogenic activity of v-Abl transformed bone marrow cells.