KRAS insertion mutations are oncogenic and exhibit distinct functional properties

Oncogenic KRAS mutations introduce discrete amino acid substitutions that reduce intrinsic Ras GTPase activity and confer resistance to GTPase-activating proteins (GAPs). Here we discover a partial duplication of the switch 2 domain of K-Ras encoding a tandem repeat of amino acids G60-A66dup in a child with an atypical myeloproliferative neoplasm. K-Ras proteins containing this tandem duplication or a similar five amino acid E62-A66dup mutation identified in lung and colon cancers transform the growth of primary myeloid progenitors and of Ba/F3 cells. Recombinant K-Ras^G60-A66dup and K-Ras^E62-A66dup proteins display reduced intrinsic GTP hydrolysis rates, accumulate in the GTP-bound conformation and are resistant to GAP-mediated GTP hydrolysis. Remarkably, K-Ras proteins with switch 2 insertions are impaired for PI3 kinase binding and Akt activation, and are hypersensitive to MEK inhibition. These studies illuminate a new class of oncogenic KRAS mutations and reveal unexpected plasticity in oncogenic Ras proteins that has diagnostic and therapeutic implications.