The induction of Egr-1 expression by v-Fps is via a protein kinase C-independent intracellular signal that is sequentially dependent upon HaRas and Raf-1.
Activating the protein-tyrosine kinase activity of v-Fps leads to the rapid transcriptional activation of the Egr-1 gene, which encodes a mitogen-responsive transcription factor. Activation of Egr-1 by v-Fps was insensitive to protein kinase C depletion, suggesting that a protein kinase C-independent signal activated by v-Fps leads to the induction of Egr-1. Expression of v-Fps in transient expression assays induced Egr-1 promoter activation. v-HaRas and v-Raf also activated the Egr-1 promoter. To characterize HaRas and Raf-1 involvement in v-Fps-induced Egr-1 expression, we used recently characterized dominant negative mutants of HaRas and Raf-1. v-Fps-induced Egr-1 promoter activation was inhibited by the dominant negative mutants of both HaRas and Raf-1. v-HaRas-induced Egr-1 promoter activation was blocked by the negative Raf-1 mutant; however, v-Raf-1-induced Egr-1 promoter activation was unaffected by the inhibitory HaRas mutant. These data suggest that v-Fps activates a protein kinase C-independent intracellular signaling pathway that is dependent on both HaRas and Raf-1, where Raf-1 functions downstream of HaRas.
Alexandropoulos
K
K
Institute for Biomolecular Structure and Function, Hunter College of The City University of New York, New York 10021.
Qureshi
S A
SA
Bruder
J T
JT
Rapp
U
U
Foster
D A
DA
D000818:Animals; D001358:Avian Sarcoma Viruses; D002460:Cell Line; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D051766:Early Growth Response Protein 1; D004789:Enzyme Activation; D015681:Fusion Proteins, gag-onc / Q000502:physiology; D005786:Gene Expression Regulation; D017874:Immediate-Early Proteins; D009154:Mutation; D015689:Oncogene Protein p21(ras) / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015398:Signal Transduction; D014157:Transcription Factors / Q000096:biosynthesis*
D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D015681:Fusion Proteins, gag-onc; D017874:Immediate-Early Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D011505:Protein-Tyrosine Kinases; C068415:v-fps oncogene protein, Fujinami sarcoma virus; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D015689:Oncogene Protein p21(ras)