The Ras-GRF1 exchange factor coordinates activation of H-Ras and Rac1 to control neuronal morphology.
The Ras-GRF1 exchange factor has regulated guanine nucleotide exchange factor (GEF) activity for H-Ras and Rac1 through separate domains. Both H-Ras and Rac1 activation have been linked to synaptic plasticity and thus could contribute to the function of Ras-GRF1 in neuronal signal transduction pathways that underlie learning and memory. We defined the effects of Ras-GRF1 and truncation mutants that include only one of its GEF activities on the morphology of PC12 phaeochromocytoma cells. Ras-GRF1 required coexpression of H-Ras to induce morphological effects. Ras-GRF1 plus H-Ras induced a novel, expanded morphology in PC12 cells, which was characterized by a 10-fold increase in soma size and by neurite extension. A truncation mutant of Ras-GRF1 that included the Ras GEF domain, GRFdeltaN, plus H-Ras produced neurite extensions, but did not expand the soma. This neurite extension was blocked by inhibition of MAP kinase activation, but was independent of dominant-negative Rac1 or RhoA. A truncation mutant of Ras-GRF1 that included the Rac GEF domains, GRFdeltaC, produced the expanded phenotype in cotransfections with H-Ras. Cell expansion was inhibited by wortmannin or dominant-negative forms of Rac1 or Akt. GRFdeltaC binds H-Ras.GTP in both pulldown assays from bacterial lysates and by coimmunoprecipitation from HEK293 cells. These results suggest that coordinated activation of H-Ras and Rac1 by Ras-GRF1 may be a significant controller of neuronal cell size.
Department of Pharmacology, Wayne State University, Detroit, MI 48201, USA.
Huibin
H
Yang
Raymond R
RR
Mattingly
D000818:Animals; D048429:Cell Size; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016501:Neurites / Q000201:enzymology / Q000502:physiology; D009474:Neurons / Q000166:cytology* / Q000201:enzymology; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017384:Sequence Deletion; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020666:ras-GRF1 / Q000235:genetics / Q000378:metabolism*
D048049:Extracellular Signal-Regulated MAP Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D016283:Proto-Oncogene Proteins p21(ras); D020830:rac1 GTP-Binding Protein; D020666:ras-GRF1