Activation and Regulation Mechanisms of the RAF Kinase Family

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BRAF, a member of the RAF family protein kinases, works in the MAPK signaling pathway, which controls broad cellular events like proliferation and differentiation. BRAF is the most frequently mutated kinase in human cancers. Furthermore, tumors lacking BRAF mutations are contingent on BRAF activity when there are mutations in upstream pathway members, such as RAS or growth factor receptors. Thus, BRAF represents an important target for cancer therapy. Despite three decades of intense research, only recently has a sufficient understanding of BRAF's mechanism creaked open the door to BRAF therapy. However, the current clinical BRAF inhibitors, vemurafenib and dabrafenib, are limited to the class I mutant BRAFV600E. Vemurafenib and dabrafenib, the two ATP-competitive inhibitors, can paradoxically activate non-BRAFV600E and wild-type BRAF, suggesting that BRAF has functions that are independent of its kinase activity. Therapeutic strategies for tumors with non- BRAFV600E mutations and wild-type BRAF are still lacking. Gaps in our knowledge contributed to the limitations of ATP-competitive BRAF drugs. The proposed work centers around three questions regarding RAF activation and regulation in health and disease states. Q1: how BRAF structural elements and ATP binding mediate the catalytic-independent functions of non-BRAFV600E and wild-type BRAF? Q2: what is the mechanism of action of the first BRAF allosteric inhibitor developed by our group and how can inhibitors targeting the catalytic and non- catalytic functions of BRAF be developed? Q3: What factors contribute to the non-overlapping functions of RAF isoforms, despite their structural similarity? The PI and her team will address these questions through multidisciplinary approaches, including X-ray crystallography, binding kinetics, phosphoproteomics, live cell imaging, chemical biology, and computational methods. Our findings will not only facilitate a better understanding of the complex biochemical mechanisms of the RAF kinase family, also provide a molecular basis for novel therapeutic approaches targeting BRAF-driven tumors.