Abstract LB-54: Identification of a RAF inhibitory auto-phosphorylation site.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Preclinical studies have demonstrated that BRAF wild-type cancer cells are not only refractory but paradoxically activate the MAPK pathway when treated with RAF inhibitors. Potentially through a related mechanism, multiple point mutations in the activation loop and Phosphate binding loop (P. loop) domains of BRAF have been characterized in human cancers, which often render BRAF catalytically impaired, yet stimulate phosphorylation of downstream targets in cells. However, the underlying biochemistry causing these phenomena has yet to be fully understood. In this study we investigate the biochemical mechanism of wild-type RAF activation in response to RAF inhibitor treatment and identify a novel auto-phosphorylation site within the well conserved BRAF/CRAF P. loop. Disruption of the auto-phosphorylation, either through pharmacologic or genetic alterations, results in activation of the MAPK pathway. This work offers new insight into RAF biochemistry by uncovering a previously unrecognized regulatory mechanism of RAF kinases that is bypassed by the BRAF oncoproteins. Citation Format: Matthew Holderfield, Hanne Merritt, Julie Lin, Zenhai Gao, Darrin Stuart, Frank McCormick. Identification of a RAF inhibitory auto-phosphorylation site. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-54. doi:10.1158/1538-7445.AM2013-LB-54