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Many aggressive epithelial cancers do not carry targetable driver mutations (Mendiratta et al. 2021, NCI-MATCH Clinical trial NCT02465060). Commonly altered signaling pathways highlight the propensity for tumors to depend on such pathways for growth and survival where genomic alterations may not be required for pathway activation. The Raf family kinases are crucial mediators of the Ras/Raf/MEK/ERK (MAPK) cascade, which has been shown to be upregulated in a subset of metastatic cancers and are mutated in many epithelial cancers. A recent study suggests non-mutated C-Raf can drive metastasis to the lungs, bone, and various other tissues (Faltermeir et al. 2016). Though the mechanism of C-Raf driven metastasis is likely through MAPK activation, C-Raf has been demonstrated to possess MAPK independent roles that may also contribute to this phenotype. In this study, we explored various C-Raf functions as drivers of metastasis in an intracardiac mouse model system. Using a series of Raf knock-out cell lines and mutants targeting functional residues in C-Raf, we demonstrated that C-Raf dimerization is necessary to drive metastasis. We further showed that the metastasis-promoting activity of C-Raf is dependent on co-expression of its family member, B-Raf, for an accelerated metastatic phenotype. However, overexpression of a kinase-dead C-Raf mutant was still able to produce metastases albeit with lower efficiency, suggesting C-Raf possesses non-kinase dependent functions that also contributed to metastasis. Together, these results point to the importance of Raf non-canonical roles in oncogenic processes that may be unappreciated in metastatic disease. Citation Format: Lisa H. Ta, Janai R. Carr-Ascher, Weixian Deng, Brandon L. Tsai, Wendy Tran, Donny Gun, Donghui Cheng, Jihui Sha, Yeonjoo Hwang, John W. Phillips, Matthew B. Obusan, Nathanael J. Bangayan, Miyako Noguchi, Zhiyuan Mao, Chia-Chun Chen, Liang Wang, Grigor Varuzhanyan, John D. Gordon, James W. Wohlschlegel, Owen N. Witte. Determining the role of non-mutated C-Raf kinase in metastatic disease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2438. |
