Mutations in G protein beta subunits promote transformation and kinase inhibitor resistance.. Homo sapiens

Activating mutations of G protein alpha subunits (Ga) occur in 4-5% of all human cancers1 but oncogenic alterations in beta subunits (Gb) have not been defined. Here we demonstrate that recurrent mutations in the Gb proteins GNB1 and GNB2 confer cytokine-independent growth and activate canonical G protein signaling. Multiple mutations in GNB1 affect the protein interface that binds Ga subunits as well as downstream effectors, and disrupt Ga-Gbg interactions. Different mutations in Gb proteins clustered to some extent based on lineage; for example, all eleven GNB1 K57 mutations were in myeloid neoplasms while 6 of 7 GNB1 I80 mutations were in B cell neoplasms. Expression of patient-derived GNB1 alleles in Cdkn2a-deficient bone marrow followed by transplantation resulted in either myeloid or B cell malignancies. In vivo treatment with the dual PI3K/mTOR inhibitor BEZ235 suppressed GNB1-induced signaling and markedly increased survival. In several human tumors, GNB1 mutations co-occurred with oncogenic kinase alterations, including BCR/ABL, JAK2 V617F and BRAF V600K. Co-expression of patient-derived GNB1 alleles with these mutant kinases resulted in inhibitor resistance in each context. Thus, GNB1 and GNB2 mutations confer transformed and resistance phenotypes across a range of human tumors and may be targetable with inhibitors of G protein signaling. Overall design: The GM-CSF dependent human cell line TF-1 was transduced with a retrovirus expressing GNB1 K89E or empty vector. RNA was extracted from cells 12 hours after withdrawal of GM-CSF and from cells maintained in GM-CSF. Biological triplicates of each condition were performed. Gene expression differences were calculated between the four conditions.