The Tumor Suppressor DiRas3 Forms a Complex with H-Ras and C-RAF Proteins and Regulates Localization, Dimerization, and Kinase Activity of C-RAF

The maternally imprinted Ras-related tumor suppressor gene DiRas3 is lost or down-regulated in more than 60% of ovarian and breast cancers. The anti-tumorigenic effect of DiRas3 is achieved through several mechanisms, including inhibition of cell proliferation, motility, and invasion, as well as induction of apoptosis and autophagy. Re-expression of DiRas3 in cancer cells interferes with the signaling through Ras/MAPK and PI3K. Despite intensive research, the mode of interference of DiRas3 with the Ras/RAF/MEK/ERK signal transduction is still a matter of speculation. In this study, we show that DiRas3 associates with the H-Ras oncogene and that activation of H-Ras enforces this interaction. Furthermore, while associated with DiRas3, H-Ras is able to bind to its effector protein C-RAF. The resulting multimeric complex consisting of DiRas3, C-RAF, and active H-Ras is more stable than the two protein complexes H-Ras·C-RAF or H-Ras·DiRas3, respectively. The consequence of this complex formation is a DiRas3-mediated recruitment and anchorage of C-RAF to components of the membrane skeleton, suppression of C-RAF/B-RAF heterodimerization, and inhibition of C-RAF kinase activity. Background: The tumor suppressor DiRas3 interferes with the Ras/MAPK mitogenic cascade. Results: DiRas3 associates with H-Ras and C-RAF and regulates localization, dimerization, and kinase activity of C-RAF. Conclusion: DiRas3 regulates the Ras/MAPK cascade at the level of Ras/RAF signal transmission. Significance: Learning how DiRas3 affects the Ras/MAPK signaling is crucial for understanding the molecular mechanisms underlying DiRas3-mediated tumor suppression.