In 2002 sequencing efforts identified a high frequency of BRAF point mutations in melanoma and in other human cancers. The ensuing decade witnessed myriad publications further characterizing the roles of mutant BRAF in numerous solid tumors and hematological malignancies. Further, it has become evident that mutations in CRAF and ARAF also occur in cancer, thus implicating the RAF family protein kinases both as drivers of oncogenesis and also as direct targets for therapeutic intervention. BRAF is mutated in ~8% of all cancers, and roughly half of all melanomas harbor a BRAFT1799A transversion, which encodes the constitutively active BRAF-V600E oncoprotein. In the original description of BRAF mutations in cancer, BRAF-V600E was only one of 14 BRAF alterations identified in cell lines and primary tumor samples14. Since then, nearly 30015 distinct missense mutations have been observed in tumor samples and cancer cell lines (Figure 1). These missense mutations encompass 115 of the 766 BRAF codons, yet the majority of mutations are observed in the activation loop (A-loop) near V600, or in the GSGSFG phosphate binding loop (P-loop) at residues 464–46915,16 (Figure 1). Crystallographic analysis revealed that the inactive conformation of BRAF is stabilized by interactions between the A- and P-loops of the BRAF kinase domain, specifically involving V600 interacting with F46817. Under normal circumstances, reversible phosphorylation of T599 and S602 in the A-loop regulates the A-loop–P-loop interaction allowing BRAF to convert back and forth from its kinase-active to the kinase-inactive state. Consequently, BRAF mutations that lead to amino acid substitutions in either the A-loop or the P-loop mimic T599 and S602 phosphorylation and, by disrupting the A-loop–P-loop interaction, irreversibly shift the equilibrium of BRAF to the kinase-active conformation.
Holderfield M, Deuker M M, McCormick F, et al. Targeting RAF kinases for cancer therapy: BRAF mutated melanoma and beyond[J]. Nature reviews. Cancer, 2014, 14(7): 455.