RhoB, not RhoA, represses the transcription of the transforming growth factor beta type II receptor by a mechanism involving activator protein 1.
The transforming growth factor-beta (TGF-beta) type I (T beta R-I) and type II (T beta R-II) receptors are responsible for transducing TGF-beta signals. We have previously shown that inhibition of farnesyltransferase activity results in an increase in T beta R-II expression, leading to enhanced TGF-beta binding, signaling, and inhibition of tumor cell growth, suggesting that a farnesylated protein(s) exerts a repressive effect on T beta R-II expression. Likely candidates are farnesylated proteins such as Ras and RhoB, which are both farnesylated and involved in cell growth control. Neither a dominant negative Ha-Ras, constitutively activated Ha-Ras, or a pharmacological inhibitor of MEK1 affected T beta R-II transcription. However, ectopic expression of RhoB, but not the closely related family member RhoA, resulted in a 5-fold decrease of T beta R-II promoter activity. Furthermore, ectopic expression of RhoB, but not RhoA, resulted in a significant decrease of T beta R-II protein expression and resistance of tumor cells to TGF-beta-mediated cell growth inhibition. Deletion analysis of the T beta R-II promoter identified a RhoB-responsive region, and mutational analysis of this region revealed that a site for the transcription factor activator protein 1 (AP1) is critical for RhoB-mediated repression of T beta R-II transcription. Electrophoretic mobility shift assays clearly showed that the binding of AP1 to its DNA-binding site is strongly inhibited by RhoB. Consequently, transcription assays using an AP1 reporter showed that AP1-mediated transcription is down-regulated by RhoB. Altogether, these results identify a mechanism by which RhoB antagonizes TGF-beta action through transcriptional down-regulation of AP1 in T beta R-II promoter.
Adnane
Jalila
J
Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute, Department of Oncology, University of South Florida, Tampa, Florida 33612, USA.
Seijo
Edward
E
Chen
Zhi
Z
Bizouarn
Francisco
F
Leal
Martha
M
Sebti
Said M
SM
Muñoz-Antonia
Teresita
T
D019883:Alkyl and Aryl Transferases / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D051231:Farnesyltranstransferase; D017353:Gene Deletion; D005799:Genes, Dominant; D006801:Humans; D007150:Immunohistochemistry; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism; D053773:Transforming Growth Factor beta1; D014407:Tumor Cells, Cultured; D020742:rhoA GTP-Binding Protein / Q000737:chemistry* / Q000378:metabolism*; D020743:rhoB GTP-Binding Protein / Q000737:chemistry* / Q000378:metabolism*
D018125:Receptors, Transforming Growth Factor beta; C508960:TGFB1 protein, human; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D020742:rhoA GTP-Binding Protein; D020743:rhoB GTP-Binding Protein