Abstract
We have identified previously undiscovered BRAF in-frame deletions near the αC-helix region of the kinase domain in pancreatic, lung, ovarian, and thyroid cancers. These deletions are mutually exclusive with KRAS mutations and occur in 4.21% of KRAS wild-type pancreatic cancer. siRNA knockdown in cells harboring BRAF deletions showed that the MAPK activity and cell growth are BRAF dependent. Structurally, the BRAF deletions are predicted to shorten the β3/αC-helix loop and hinder its flexibility by locking the helix in the active αC-helix-in conformation that favors dimer formation. Expression of L485-P490-deleted BRAF is able to transform NIH/3T3 cells in a BRAF dimer-dependent manner. BRAF homodimer is confirmed to be the dominant RAF dimer by proximity ligation assays in BRAF deletion cells, which are resistant to the BRAF inhibitor vemurafenib and sensitive to LY3009120, a RAF dimer inhibitor. In tumor models with BRAF deletions, LY3009120 has shown tumor growth regression, whereas vemurafenib is inactive. This study discovered oncogenic BRAF deletions with a distinct activation mechanism dependent on the BRAF dimer formation in tumor cells. LY3009120 is active against these cells and represents a potential treatment option for patients with cancer with these BRAF deletions, or other atypical BRAF mutations where BRAF functions as a dimer.
Highlights
Somatic mutations in the BRAF gene were discovered in 2002 in melanoma, where they behave as potent oncogenes and activate downstream MAPK signaling and cancer cell growth [1,2,3,4,5]
In an unbiased screen of a large panel of tumor cell lines for their sensitivity to MAPK pathway inhibitors, we observed that BxPC-3 cells were very sensitive to the RAF dimer inhibitor LY3009120, but not sensitive to the BRAF-selective inhibitors vemurafenib or dabrafenib [36]
When we carefully evaluated these data for mutations in RAS pathway genes in BxPC-3 cells, including small in-frame deletions which are easy to be ignored by routine data analysis, we discovered that BxPC-3 cells have a 5-amino acid deletion near the αC-helix region of the BRAF kinase domain (V487-P492>A)
Summary
Somatic mutations in the BRAF gene were discovered in 2002 in melanoma, where they behave as potent oncogenes and activate downstream MAPK signaling and cancer cell growth [1,2,3,4,5]. In addition to missense mutations, oncogenic BRAF fusions were identified in cancers of the thyroid and prostate, melanoma, and astrocytomas [14,15,16,17,18,19]. These fusions either encode protein partners that contribute coiled-coil (CC) or zinc-finger dimerization motifs to produce constitutively activated BRAF dimers, or remove at least the first eight exons of BRAF that are known to promote BRAF dimerization
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
