¹Departments of Radiation Oncology and Pharmacology, CB 7512, Lineberger Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, NC 27599, USA

²Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, NC 27599, USA

³Department of Biochemistry, University of Kentucky, Lexington, Kentucky, KY 40536, USA

⁴Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA

Correspondence to: D Cox, Departments of Radiation Oncology and Pharmacology, CB 7512, Lineberger Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, NC 27599, USA

The biological functions of Rit (Ras-like protein in tissues) and Rin (Ras-like protein in neurons), members of a novel branch of Ras-related GTP-binding proteins that are ~50% identical to Ras, have not been characterized. Therefore, we assessed their activity in growth control, transformation and signaling. NIH cells stably expressing a constitutively activated mutant of Rit [Rit(79L)] (analogous to the oncogenic mutant H-Ras(61L)) demonstrated strong growth transformation, proliferating rapidly in low serum and forming colonies in soft agar and tumors in nude mice. Although Rit(79L) alone did not promote morphologically transformed foci, it cooperated with both Raf and Rho A to form Rac/Rho-like foci. Rin [Rin(78L)] cooperated only with Raf. Rit(79L) but not Rin(78L) stimulated transcription from luciferase reporter constructs regulated by SRF, NF-B, Elk-1 and Jun. However, neither activated ERK, JNK or p38, or PI3-K/Akt kinases in immune complex kinase assays. Interestingly, although Rit lacks any known recognition signal for C-terminal lipidation, Rit-transformed cell growth and survival in low serum is dependent on a farnesylated protein, as treatment with farnesyltransferase inhibitors caused apoptosis. Rin cooperated with Raf in focus assays but did not otherwise function in these assays, perhaps due to a lack of appropriate effector pathways in NIH3T3 fibroblasts for this neural-specific Ras family member. In summary, although Rit shares most core effector domain residues with Ras, our results suggest that Rit uses novel effector pathways to regulate proliferation and transformation. Oncogene (2000) 19, 4685-4694

Rit; Ras; signaling; transformation; lipid modification; farnesyltransferase