Phosphatidylinositol 3 kinase contributes to the transformation of hematopoietic cells by the D816V c-Kit mutant

Stem cell factor (SCF) binds the receptor tyrosine kinase c-Kit and Is crit ical for normal hematopoiesis. Substitution of valine for aspartic acid 816 (D816V) constitutively actives human c-Kit, and this mutation is found in patients with mastocytosis, leukemia, and germ cell tumors. Immortalized mu rine progenitor cells (MIHCs) transduced with wild-type c-Kit proliferate i n response to SCF, whereas cells expressing D816V c-Kit (MIHC-D816V) are fa ctor-independent and tumorigenic. However, the mechanisms mediating transfo rmation by D816V c-Kit are unknown. The objective of this study was to iden tify signaling components that contribute to D816V c-Kit-mediated transform ation. SCIF stimulates association of p85(PI3K) with phosphorylated tyrosin e 721 of wild-type c-Kit. Phosphatidylinositol 3 kinase (PI3K) subsequently contributes to the activation at Akt and Jnks. In contrast, these studies demonstrated that the D816V c-Kit mutant was constitutively associated with phosphorylated p85(PI3K), and, downstream of PI3K, Jnk 1 and Jnk 2 were ac tivated but Akt was not. Interestingly, Erks 1 and 2 were not constitutivel y activated by D816V c-Kit. Thus, D816V c-Kit maintains the activity of PI3 K but not of all signaling pathways activated by wild-type c-Kit. Further, all pathways downstream at PI3K are not constitutively active in MIHC-D816V cells. Studies with a PI3K inhibitor and D816V/Y721F c-Kit, a mutant incap able of recruiting PI3K, indicate that constitutive activation of PI3K thro ugh direct recruitment by D816V c-Kit plays a role in factor-independent gr owth at MIHC and is critical for tumorigenicity. (C) 2001 by The American S ociety of Hematology.