The small-GTPase RalA activates transcription of the urokinase plasminogen activator receptor (uPAR) gene via an AP1-dependent mechanism.
The urokinase plasminogen activator receptor (uPAR) focuses extracellular protease activity to the cell surface, modulates cell adhesion and activates intracellular signal transduction pathways. In a range of cancers uPAR expression often has a negative correlation with prognosis. Here we show that uPAR transcription is stimulated by V12 H-Ras, the effector loop mutant V12 H-Ras G37 and constitutively-active RalA 72L. RalA-dependent transcription required the presence of the ATF2-like AP1-site at -70 bp and the c-Jun binding motif at -184 bp in the uPAR promoter. Consistent with this, both Gal4-c-Jun- and Gal4-ATF2-fusion proteins were activated by RalA signalling through phosphorylation of their activation domains at Ser63 and Ser73 of c-Jun or Thr69 and Thr71 of ATF2. A transdominant inhibitory mutant of c-Jun N-terminal kinase (JNK) failed to inhibit uPAR transcription demonstrating that JNK activation is not a prerequisite for RalA-dependent uPAR transcription. A dominant negative inhibitor of c-Src effectively inhibited RalA-dependent uPAR transcription identifying it as a downstream effector in the RalA signalling pathway. These data provide evidence for the existence of a novel signalling pathway that links RalA to the activation of uPAR transcription via a c-Src intermediate and activation of AP1.
Okan
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School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham, NG7 2UH, UK.
Drewett
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V
Shaw
P E
PE
Jones
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P
D051698:Activating Transcription Factor 2; D001483:Base Sequence; D000081247:CSK Tyrosine-Protein Kinase; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000502:physiology*; D011905:Genes, ras; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics*; D055293:Receptors, Urokinase Plasminogen Activator; D020218:Response Elements; D015534:Trans-Activators / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D020725:ral GTP-Binding Proteins; D019061:src-Family Kinases
C497105:ATF2 protein, human; D051698:Activating Transcription Factor 2; D017362:Cyclic AMP Response Element-Binding Protein; C524898:PLAUR protein, human; D016755:Proto-Oncogene Proteins c-jun; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D020558:GTP Phosphohydrolases; C492198:RALA protein, human; D020725:ral GTP-Binding Proteins