R-Ras3/M-Ras induces neuronal differentiation of PC12 cells through cell-type-specific activation of the mitogen-activated protein kinase cascade.
R-Ras3/M-Ras is a novel member of the Ras subfamily of GTP-binding proteins which has a unique expression pattern highly restricted to the mammalian central nervous system. In situ hybridization using an R-Ras3 cRNA probe revealed high levels of R-Ras3 transcripts in the hippocampal region of the mouse brain as well as a pattern of expression in the cerebellum that was distinct from that of H-Ras. We found that R-Ras3 was activated by nerve growth factor (NGF) and basic fibroblast growth factor as well as by the guanine nucleotide exchange factor GRP but not by epidermal growth factor. Ectopic expression of either R-Ras3 or GRP in PC12 cells induced efficient neuronal differentiation. The ability of NGF as well as GRP to promote differentiation of PC12 cells was attenuated by an R-Ras3 dominant-negative mutant. Furthermore, the biological action of R-Ras3 in PC12 cells was dependent on the mitogen-activated protein kinase (MAPK). Interestingly, whereas R-Ras3 was unable to mediate efficient activation of MAPK activity in NIH 3T3 cells, it was able to do so in PC12 cells. This cell-type specificity is in stark contrast to that of H-Ras, which can stimulate the MAPK pathway in both cell types. Indeed, this pattern of MAPK activation could be explained by the fact that R-Ras3 was unable to activate c-Raf, while it bound and stimulated the neuronal Raf isoform, B-Raf, in PC12 cells. Thus, R-Ras3 is implicated in a novel pathway of neuronal differentiation by coupling specific trophic factors to the MAPK cascade through the activation of B-Raf.
The Derald H. Ruttenberg Cancer Center, The Mount Sinai School of Medicine, New York, New York 10029, USA.
Alec C
AC
Kimmelman
Nelson
N
Nuñez Rodriguez
Andrew M-L
AM
Chan
D016475:3T3 Cells; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D006801:Humans; D017403:In Situ Hybridization; D007202:Indicators and Reagents / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020932:Nerve Growth Factor / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D016716:PC12 Cells; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
D004791:Enzyme Inhibitors; D007202:Indicators and Reagents; D008164:Luminescent Proteins; C109523:MRAS protein, human; D049452:Green Fluorescent Proteins; D006160:Guanosine Triphosphate; D020932:Nerve Growth Factor; C482120:Braf protein, mouse; C482123:Braf protein, rat; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins