Proto-oncogenic H-Ras, K-Ras, and N-Ras are involved in muscle differentiation via phosphatidylinositol 3-kinase.
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.
Lee
Jisun
J
Department of Biochemistry and Molecular Biology, Medical Research Center for Bioreaction to Reactive Oxygen Species and Biomedical Science Institute, Kyung Hee University, Seoul, Korea.
Choi
Kyu Jin
KJ
Lim
Min Jin
MJ
Hong
Feng
F
Choi
Tae Gyu
TG
Tak
Eunyoung
E
Lee
Seonmin
S
Kim
Young-Joo
YJ
Chang
Sung Goo
SG
Cho
Jin Man
JM
Ha
Joohun
J
Kim
Sung Soo
SS
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
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)