PI3 Kinase mediates transformation of hematopoietic cells by the V816 c-kit mutant

C-Kit is a receptor tyrosine kinase that binds stem cell factor. Substitution of valine for aspartic acid 816 (V816) constitutively activates human c-Kit and this mutation is found in patients with mastocytosis, leukemia and germ cells tumors. Transduction of immortalized murine progenitor cells with wild-type c-Kit (MIHC-Kit) results in stem cell factor-induced growth (SCF), while cells expressing V816 c-Kit (MIHC-V816) are factor-independent and tumorigenic. The mechanisms mediating transformation by V816 c-Kit are unknown. SCF activates Erk 1, Erk2 and P13 kinase in MIHC-Kit cells, and P13 kinase contributes to activation of Akt and Jnks. In MIHC-V816 cells, P13 kinase, Jnk 1 and Jnk 2 were activated, but Akt, Erk 1 and Erk 2 were not. Thus, V816 c-Kit constitutively activates P13 kinase, but not all signaling pathways activated by wild-type c-Kit. Further, pathways downstream of P13 kinase are altered in MIHC-V816 cells. Studies with a P13 kinase inhibitor and V816/F721 c-Kit, a mutant incapable of recruiting P13 kinase, indicate that constitutive activation of P13 kinase plays a role in factor-independent growth mediated by V816 c-Kit and is critical for tumorigenicity of MIHC. These data are the first to demonstrate the role of P13 kinase in transformation of hematopoietic cells by this oncogenic c-Kit mutant.