TC21 causes transformation by Raf-independent signaling pathways.
Although the Ras-related protein TC21/R-Ras2 has only 55% amino acid identity with Ras proteins, mutated forms of TC21 exhibit the same potent transforming activity as constitutively activated forms of Ras. Therefore, like Ras, TC21 may activate signaling pathways that control normal cell growth and differentiation. To address this possibility, we determined if regulators and effectors of Ras are also important for controlling TC21 activity. First, we determined that Ras guanine nucleotide exchange factors (SOS1 and RasGRF/CDC25) synergistically enhanced wild-type TC21 activity in vivo and that Ras GTPase-activating proteins (GAPs; p120-GAP and NF1-GAP) stimulated wild-type TC21 GTP hydrolysis in vitro. Thus, extracellular signals that activate Ras via SOS1 activation may cause coordinate activation of Ras and TC21. Second, we determined if Raf kinases were effectors for TC21 transformation. Unexpectedly, yeast two-hybrid binding analyses showed that although both Ras and TC21 could interact with the isolated Ras-binding domain of Raf-1, only Ras interacted with full-length Raf-1, A-Raf, or B-Raf. Consistent with this observation, we found that Ras- but not TC21-transformed NIH 3T3 cells possessed constitutively elevated Raf-1 and B-Raf kinase activity. Thus, Raf kinases are effectors for Ras, but not TC21, signaling and transformation. We conclude that common upstream signals cause activation of Ras and TC21, but activated TC21 controls cell growth via distinct Raf-independent downstream signaling pathways.
Graham
S M
SM
Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill 27599, USA.
Vojtek
A B
AB
Huff
S Y
SY
Cox
A D
AD
Clark
G J
GJ
Cooper
J A
JA
Der
C J
CJ
D016475:3T3 Cells; D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D002471:Cell Transformation, Neoplastic; D005260:Female; D005656:Fungal Proteins / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D020690:GTPase-Activating Proteins; D011905:Genes, ras; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism*; D051379:Mice; D020559:Monomeric GTP-Binding Proteins; D009928:Organ Specificity; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011247:Pregnancy; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D020837:SOS1 Protein; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins / Q000378:metabolism*; D020666:ras-GRF1
D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D020690:GTPase-Activating Proteins; D008565:Membrane Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D020837:SOS1 Protein; D020703:ras GTPase-Activating Proteins; D020666:ras-GRF1; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D010749:Phosphoprotein Phosphatases; C087360:RRAS2 protein, human; C490200:Rras2 protein, mouse; D019204:GTP-Binding Proteins; D020559:Monomeric GTP-Binding Proteins; D018631:ras Proteins