A critical role for PLCG1 in RAS activation by BCR-ABL1 and FLT3-ITD

Myeloid leukemias are frequently associated with pathologically activating mutations in tyrosine kinases [BCR-ABL1 in chronic myeloid leukemia (CML); FLT3 juxtamembrane internal tandem duplication (ITD) mutations, FLT3 and KIT activation loop mutations in acute myeloid leukemia (AML)]. Mutations in these kinases activate RAS, which initiates multiple downstream signaling pathways that regulate cell proliferation, differentiation, and apoptosis. The mechanisms whereby RAS is activated by these kinases is incompletely understood, and a better understanding of the molecular mediators involved in RAS activation may uncover new therapeutic strategies. Here we identify a biologically and therapeutically important novel mechanism whereby BCR-ABL1 and FLT3-ITD activate the critical downstream effector RAS in part through phospholipase C gamma-1 (PLCG1). PLCG1 knockout decreases proliferation of CML and FLT3-ITD-expressing AML cells, reduces RAS nucleotide exchange factor activity, and increases sensitivity of CML cells to BCR-ABL1 tyrosine kinase inhibitors (TKIs). Collectively, these studies suggest that PLCG1 inhibition may augment clinical responses to BCR-ABL1 and FLT3 TKIs in CML and AML.