title: Proto-oncogenic H-Ras, K-Ras, and N-Ras are involved in muscle differentiation via phosphatidylinositol 3-kinase.
abstract: Oncogenic H-Ras G12V and its variants have been shown to inhibit muscle differentiation. However, the role of proto-oncogenic Ras (c-Ras) in muscle differentiation remains unclear. The active GTP-bound form of Ras has been known to associate with diverse effectors including Raf, phosphatidylinositol 3-kinase (PI3K), Ral-GDS, and other molecules to transmit downstream signals. We hypothesize that c-Ras may stimulate muscle differentiation by selectively activating PI3K, an important mediator for muscle differentiation. In our experiments, inhibition of c-Ras by farnesyltransferase inhibitors and a dominant negative form of H-Ras (Ras S17N) suppressed muscle differentiation. Consistently, individual knockdown of H-Ras, K-Ras, and N-Ras by siRNAs all blocked muscle differentiation. Interestingly, we found that c-Ras preferentially interacts with PI3K rather than its major binding partner c-Raf, during myogenic differentiation, with total c-Ras activity remaining unchanged. PI3K and its downstream myogenic pathway, the Nox2/NF-kappaB/inducible nitric oxide synthase (iNOS) pathway, were found to be suppressed by inhibition of c-Ras activity during differentiation. Furthermore, expression of a constitutively active form of PI3K completely rescued the differentiation block and reactivated the Nox2/NF-kappaB/iNOS pathway in c-Ras-inhibited cells. On the basis of our results, we conclude that contrary to oncogenic Ras, proto-oncogenic H-Ras, K-Ras, and N-Ras are directly involved in the promotion of muscle differentiation via PI3K and its downstream signaling pathways. In addition, PI3K pathway activation is associated with a concurrent suppression of the otherwise predominantly activated Raf/Mek/Erk pathway.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical Research Center for Bioreaction to Reactive Oxygen Species and Biomedical Science Institute, Kyung Hee University, Seoul, Korea.
authors.forename: Jisun
authors.initials: J
authors.lastname: Lee
authors.forename: Kyu Jin
authors.initials: KJ
authors.lastname: Choi
authors.forename: Min Jin
authors.initials: MJ
authors.lastname: Lim
authors.forename: Feng
authors.initials: F
authors.lastname: Hong
authors.forename: Tae Gyu
authors.initials: TG
authors.lastname: Choi
authors.forename: Eunyoung
authors.initials: E
authors.lastname: Tak
authors.forename: Seonmin
authors.initials: S
authors.lastname: Lee
authors.forename: Young-Joo
authors.initials: YJ
authors.lastname: Kim
authors.forename: Sung Goo
authors.initials: SG
authors.lastname: Chang
authors.forename: Jin Man
authors.initials: JM
authors.lastname: Cho
authors.forename: Joohun
authors.initials: J
authors.lastname: Ha
authors.forename: Sung Soo
authors.initials: SS
authors.lastname: Kim
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D005204:Farnesol / Q000031:analogs & derivatives / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism; D024510:Muscle Development; D009206:Myocardium / Q000166:cytology; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D012459:Salicylates / Q000494:pharmacology; D015398:Signal Transduction
chemical_list: D008562:Membrane Glycoproteins; D016328:NF-kappa B; D034741:RNA, Small Interfering; D012459:Salicylates; C093323:farnesylthiosalicylic acid; D009569:Nitric Oxide; D005204:Farnesol; D052247:Nitric Oxide Synthase Type II; C500593:Cybb protein, rat; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D019869:Phosphatidylinositol 3-Kinases; D016283:Proto-Oncogene Proteins p21(ras)