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Castillo S, Gence R, Pagan D, Koraïchi F, Bouchenot C, Pons BJ, Boëlle B, Olichon A, Lajoie-Mazenc I, Favre G, Pédelacq JD, Cabantous S. Visualizing the subcellular localization of RHOB-GTP and GTPase-Effector complexes using a split-GFP/nanobody labelling assay. Eur J Cell Biol 2023; 102:151355. [PMID: 37639782 DOI: 10.1016/j.ejcb.2023.151355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 08/04/2023] [Accepted: 08/20/2023] [Indexed: 08/31/2023] Open
Abstract
Small GTPases are highly regulated proteins that control essential signaling pathways through the activity of their effector proteins. Among the RHOA subfamily, RHOB regulates peculiar functions that could be associated with the control of the endocytic trafficking of signaling proteins. Here, we used an optimized assay based on tripartite split-GFP complementation to localize GTPase-effector complexes with high-resolution. The detection of RHOB interaction with the Rhotekin Rho binding domain (RBD) that specifically recognizes the active GTP-bound GTPase, is performed in vitro by the concomitant addition of recombinant GFP1-9 and a GFP nanobody. Analysis of RHOB-RBD complexes localization profiles combined with immunostaining and live cell imaging indicated a serum-dependent reorganization of the endosomal and membrane pool of active RHOB. We further applied this technology to the detection of RHO-effector complexes that highlighted their subcellular localization with high resolution among the different cellular compartments.
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Affiliation(s)
- Sebastian Castillo
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France
| | - Rémi Gence
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France
| | - Delphine Pagan
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France
| | - Faten Koraïchi
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France
| | | | - Benoit J Pons
- Environment and Sustainability Institute, Biosciences, University of Exeter, Penryn TR10 9FE, United Kingdom
| | - Betty Boëlle
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France
| | - Aurélien Olichon
- Université de la Réunion, INSERM, UMR 1188 Diabète Athérothrombose Thérapies Réunion Océan Indien (DéTROI), 97410 Saint-Pierre, La Réunion, France
| | - Isabelle Lajoie-Mazenc
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France
| | - Gilles Favre
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France
| | - Jean-Denis Pédelacq
- Institut de Pharmacologie et de Biologie Structurale (IPBS), Université de Toulouse, CNRS, Université Toulouse III - Paul Sabatier (UPS), Toulouse, France
| | - Stéphanie Cabantous
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, UPS, CNRS, 31037 Toulouse, France.
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Pham TD, Ravi V, Fan C, Luo B, Sun XF. Tensor Decomposition of Largest Convolutional Eigenvalues Reveals Pathologic Predictive Power of RhoB in Rectal Cancer Biopsy. Am J Pathol 2023; 193:579-590. [PMID: 36740183 DOI: 10.1016/j.ajpath.2023.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Revised: 12/29/2022] [Accepted: 01/06/2023] [Indexed: 02/05/2023]
Abstract
RhoB protein belongs to the Rho GTPase family, which plays an important role in governing cell signaling and tissue morphology. RhoB expression is known to have implications in pathologic processes of diseases. Investigation in the regulation and communication of this protein, detected by immunohistochemical staining on the microscope, is worth exploring to gain insightful information that may lead to identifying optimal disease treatment options. In particular, the role of RhoB in rectal cancer is not well discovered. Here, we report that methods of deep learning-based image analysis and the decomposition of multiway arrays discover the predictive factor of RhoB in two cohorts of patients with rectal cancer having survival rates of <5 and >5 years. The analysis results show distinctions between the tensor decomposition factors of the two cohorts.
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Affiliation(s)
- Tuan D Pham
- Center for Artificial Intelligence, Prince Mohammad Bin Fahd University, Khobar, Saudi Arabia.
| | - Vinayakumar Ravi
- Center for Artificial Intelligence, Prince Mohammad Bin Fahd University, Khobar, Saudi Arabia
| | - Chuanwen Fan
- Department of Clinical and Experimental Medicine, Linkoping University, Linkoping, Sweden
| | - Bin Luo
- Department of Clinical and Experimental Medicine, Linkoping University, Linkoping, Sweden; Department of Gastrointestinal Surgery, Sichuan Provincial People's Hospital, Chengdu, China
| | - Xiao-Feng Sun
- Department of Clinical and Experimental Medicine, Linkoping University, Linkoping, Sweden
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3
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Abstract
RhoB is a Rho family GTPase that is highly similar to RhoA and RhoC, yet has distinct functions in cells. Its unique C-terminal region is subject to specific post-translational modifications that confer different localization and functions to RhoB. Apart from the common role with RhoA and RhoC in actin organization and cell migration, RhoB is also implicated in a variety of other cellular processes including membrane trafficking, cell proliferation, DNA-repair and apoptosis. RhoB is not an essential gene in mice, but it is implicated in several physiological and pathological processes. Its multiple roles will be discussed in this review.
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Affiliation(s)
- Francisco M. Vega
- Instituto de Biomedicina de Sevilla, IBiS (Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla), Sevilla, Spain
- Department of Medical Physiology and Biophysics, Universidad de Sevilla, Sevilla, Spain
| | - Anne J. Ridley
- Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, Guy's Campus, London, UK
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Pérez-Sala D, Boya P, Ramos I, Herrera M, Stamatakis K. The C-terminal sequence of RhoB directs protein degradation through an endo-lysosomal pathway. PLoS One 2009; 4:e8117. [PMID: 19956591 PMCID: PMC2780327 DOI: 10.1371/journal.pone.0008117] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2009] [Accepted: 11/05/2009] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Protein degradation is essential for cell homeostasis. Targeting of proteins for degradation is often achieved by specific protein sequences or posttranslational modifications such as ubiquitination. METHODOLOGY/PRINCIPAL FINDINGS By using biochemical and genetic tools we have monitored the localization and degradation of endogenous and chimeric proteins in live primary cells by confocal microscopy and ultra-structural analysis. Here we identify an eight amino acid sequence from the C-terminus of the short-lived GTPase RhoB that directs the rapid degradation of both RhoB and chimeric proteins bearing this sequence through a lysosomal pathway. Elucidation of the RhoB degradation pathway unveils a mechanism dependent on protein isoprenylation and palmitoylation that involves sorting of the protein into multivesicular bodies, mediated by the ESCRT machinery. Moreover, RhoB sorting is regulated by late endosome specific lipid dynamics and is altered in human genetic lipid traffic disease. CONCLUSIONS/SIGNIFICANCE Our findings characterize a short-lived cytosolic protein that is degraded through a lysosomal pathway. In addition, we define a novel motif for protein sorting and rapid degradation, which allows controlling protein levels by means of clinically used drugs.
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Affiliation(s)
- Dolores Pérez-Sala
- Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
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Vignal E, de Santa Barbara P, Guémar L, Donnay JM, Fort P, Faure S. Expression of RhoB in the developing Xenopus laevis embryo. Gene Expr Patterns 2006; 7:282-8. [PMID: 17049930 DOI: 10.1016/j.modgep.2006.09.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Revised: 09/05/2006] [Accepted: 09/06/2006] [Indexed: 10/24/2022]
Abstract
Rho GTPases are signaling components that participate to the control of cell morphology, adhesion and motility through the regulation of F-actin cytoskeleton dynamics. In this paper, we report the identification of RhoB in Xenopus laevis (XRhoB) and its expression pattern during early development. Whole-mount in situ hybridization analysis indicated that XrhoB is expressed at high levels in the dorsal marginal zone early in gastrula and in the dorsal midline at later stages. At mid-neurula stages, XrhoB expression extends to the central nervous system, presomitic mesoderm and somites. Later during development, rhoB mRNA is detected in the eyes, the migrating neural crest cells as well as the dorso-lateral part of the somites.
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Affiliation(s)
- Emmanuel Vignal
- Centre de Recherches en Biochimie Macromoléculaire, FRE 2593 CNRS, 1919 route de Mende, 34293 Montpellier, France
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Lee YJ, Heitzman CE, Frei WR, Johnson HT, Braun PV. Transformation of Hydrogel-Based Inverse Opal Photonic Sensors from FCC to L11 during Swelling. J Phys Chem B 2006; 110:19300-6. [PMID: 17004784 DOI: 10.1021/jp0638540] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The structural evolution of Bragg diffracting inverse opal hydrogel sensors during swelling is directly observed by two-photon laser scanning fluorescence microscopy and compared to predictions from finite element analysis. A fluorescently labeled pH-sensitive hydrogel is UV-polymerized in a dried polystyrene colloidal crystal template, which is etched to yield an inverse opal. Fluorescence imaging of the hydrogel at different pH values reveals an inhomogeneous deformation of the FCC array of aqueous pores. The pores elongate along the sample normal direction and collapse along the sample parallel directions, consistent with the Bragg response, which indicates a 1-D increase in the interlayer distance. Interconnects between the pores serve as anchor points during hydrogel expansion into the pores. Pinning of the hydrogel to the substrate causes a change of the hydrogel lattice symmetry during deformation, from FCC (ABC stacking) to L1(1) (ABCA'B'C' stacking). Reconstructed cross-sections confirm that a 1-D increase in the interlayer distance along the substrate normal direction is responsible for the diffraction response of an inverse opal hydrogel sensor. Comparison with predictions from finite element analysis shows qualitative agreement, although the experimental mesostructure is significantly more deformed than the calculated data, due to buckling in the experimental system that is not captured by the model.
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Affiliation(s)
- Yun-Ju Lee
- Department of Materials Science and Engineering, Beckman Institute for Advanced Science and Technology, and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, 61801, USA
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Abstract
RhoB is a small GTP-binding protein that is involved in apoptotic signal transduction. We have cloned the mouse RhoB mRNA including a 1377 nucleotide 3'-untranslated region (UTR) that contains six AU-rich elements (AREs) as well as several uridine-rich stretches. There is 94% homology overall between the mouse and rat RhoB genes and 92% homology between the mouse and a putative human clone. Ultraviolet light (UVL) induces RhoB production through regulated changes in gene transcription and mRNA stabilization although the latter mechanism is unknown. We observed that UVL increased the half-life of RhoB mRNA from 63 min to 3.3 h in NIH/3T3 cells and from 87 min to 2.7 h in normal human keratinocyte cells. In vitro mobility shift assays demonstrated that HuR bound the 3'-UTR of RhoB at three distinct locations (nucleotides 1342-1696, 1765-1920 and 1897-1977) suggesting a regulatory role for this RNA-binding protein. HuR immunoprecipitations were positive for RhoB mRNA indicating an in vivo association, and Western blot analysis and immunofluorescence demonstrated that HuR rapidly partitions from the nucleus to the cytoplasm after UVL. Therefore, we propose a model in which UVL induces stress-activated signal transduction leading to nuclear/cytoplasmic shuttling of HuR and subsequent stabilization of RhoB mRNA.
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Affiliation(s)
- Cara J Westmark
- Department of Pathology and Laboratory Medicine, Waisman Center for Developmental Disabilities, University of Wisconsin, Madison, WI 53705, USA
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Abstract
RhoA and RhoB share 86% amino acid sequence identity, yet RhoA promotes whereas RhoB suppresses malignant transformation. Amino acids 29, 100, 116, 123, 129, 140-143, 141, 146, 152, 154, 155, 173, 181, 183-187, 189, 190, 191, 192, and 193 in RhoB were mutated to the corresponding RhoA residues to determine those critical for RhoB tumor-suppressive activity. Of all the mutants made, only the cysteine 192 (one of two palmitoylation sites) and cysteine 193 (the prenylation site) point mutations abolish RhoB functions. In contrast, mutation of the other palmitoylation site, cysteine 189, did not affect RhoB functions. Moving cysteine 192 to position 190 did not affect RhoB function either. Mutation of cysteine 192 to glycine, alanine, or serine blocks the ability of RhoB to suppress transforming growth factor beta type II receptor, p2lwaf, and AP-1 promoter transcriptional activities. Furthermore, mutations of cysteines 192 and 193, but not 189, mislocalize RhoB and prevent RhoB from inhibiting anchorage-dependent and anchorage-independent tumor growth and colony formation as well as prevent it from inducing apoptosis. The cysteine 192 RhoB mutant is farnesylated and geranylgeranylated as efficiently as wild type RhoB. A RhoA-(1-180)/RhoB-(181-196) chimera inhibited tumor cell proliferation and induced apoptosis as efficiently as RhoB. These results demonstrate that the presence of neither cysteine 193 nor cysteine 192 alone is sufficient and that both palmitoylated cysteine 192 and prenylated cysteine 193, but not palmitoylated cysteine 189, are required for RhoB tumor-suppressive and proapoptotic activities.
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Affiliation(s)
- De-An Wang
- Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute, Department of Interdisciplinary Oncology, Tampa, Florida 33612, USA
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9
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Abstract
The Rho family GTPases RhoA, RhoB, and RhoC regulate the actin cytoskeleton, cell movement, and cell growth. Unlike Ras, up-regulation or overexpression of these GDP/GTP binding molecular switches, but not activating point mutations, has been associated with human cancer. Although they share over 85% sequence identity, RhoA, RhoB, and RhoC appear to play distinct roles in cell transformation and metastasis. In NIH 3T3 cells, RhoA or RhoB overexpression causes transformation whereas RhoC increases the cell migration rate. To specifically target RhoA, RhoB, or RhoC function, we have generated a set of chimeric molecules by fusing the RhoGAP domain of p190, a GTPase-activating protein that accelerates the intrinsic GTPase activity of all three Rho GTPases, with the C-terminal hypervariable sequences of RhoA, RhoB, or RhoC. The p190-Rho chimeras were active as GTPase-activating proteins toward RhoA in vitro, co-localized with the respective active Rho proteins, and specifically down-regulated Rho protein activities in cells depending on which Rho GTPase sequences were included in the chimeras. In particular, the p190-RhoA-C chimera specifically inhibited RhoA-induced transformation whereas p190-RhoC-C specifically reversed the migration phenotype induced by the active RhoC. In human mammary epithelial-RhoC breast cancer cells, p190-RhoC-C, but not p190-RhoA-C or p190-RhoB-C, reversed the anchorage-independent growth and invasion phenotypes caused by RhoC overexpression. In the highly metastatic A375-M human melanoma cells, p190-RhoC-C specifically reversed migration, and invasion phenotypes attributed to RhoC up-regulation. Thus, we have developed a novel strategy utilizing RhoGAP-Rho chimeras to specifically down-regulate individual Rho activity and demonstrate that this approach may be applied to multiple human tumor cells to reverse the growth and/or invasion phenotypes associated with disregulation of a distinct subtype of Rho GTPase.
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Affiliation(s)
- Lei Wang
- Division of Experimental Hematology and Molecular Developmental Biology Program, Children's Hospital Research Foundation, University of Cincinnati, Cincinnati, Ohio 45229, USA
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10
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Abstract
The small GTPase-encoding gene RhoB is strongly induced as part of the immediate early response of serum-stimulated fibroblasts. In this report, we have characterized the mechanism for growth factor responsiveness of RhoB in Rat-2 fibroblasts. By Northern blotting and ribonuclease protection, we observed low or barely detectable levels of RhoB mRNA in quiescent cells, but expression was transiently induced in response to serum stimulation, such that the mRNA peaked within 30 min and then declined over the next hour. Analysis of the rat promoter revealed cis-elements conserved with the mouse and human genes, including a pair of CEBP sites near the transcriptional start site. However, in contrast to the analysis of RNA, RhoB promoter fusions were constitutively expressed in quiescent cells in transient transfections, and were unaffected by serum. Similarly, stable RhoB promoter integrants were highly expressed in quiescent cells, and growth factor caused a slight decrease in activity. This indicates that growth factor-inducible RhoB expression cannot be mediated by transcriptional activation. We then examined decay of the RhoB mRNA and found that serum caused significant stabilization. Additionally, fusion of the 3' RhoB untranslated region (UTR) to a constitutively expressed reporter gene caused serum and growth factor as well as DNA damage-inducible expression. These observations are consistent with the view that RhoB mRNA is produced constitutively but its abundance is controlled in response to growth factors, and other signals including DNA damage, by stabilization through elements within the 3' UTR.
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Affiliation(s)
- Tom Malcolm
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2146 Health Sciences Mall, Vancouver, B.C., Canada V6 T 1Z3
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11
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Stamatakis K, Cernuda-Morollón E, Hernández-Perera O, Pérez-Sala D. Isoprenylation of RhoB is necessary for its degradation. A novel determinant in the complex regulation of RhoB expression by the mevalonate pathway. J Biol Chem 2002; 277:49389-96. [PMID: 12384510 DOI: 10.1074/jbc.m204049200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Statins improve vascular functions by mechanisms independent from their cholesterol-lowering effect. Rho GTPases are emerging as key targets for the vascular effects of statins. RhoB is a short-lived, early-response inducible protein involved in receptor endocytosis, apoptosis, and gene expression. Here we show that statins regulate RhoB expression by acting at multiple levels. Simvastatin increased RhoB protein levels by 8- to 10-fold. This effect was related to a depletion of isoprenoid intermediates, as deduced from the observation that several metabolites of the cholesterol biosynthetic pathway, namely, mevalonate and geranylgeranyl-pyrophosphate, attenuated simvastatin-induced RhoB up-regulation. Moreover, prenyltransferase inhibitors mimicked simvastatin effect. Cholesterol supplementation did not prevent simvastatin-elicited up-regulation but increased RhoB levels per se. Simvastatin moderately augmented RhoB transcript levels, but markedly impaired the degradation of RhoB protein, which accumulated in the cytosol in its non-isoprenylated form. Inhibition of RhoB isoprenylation was apparently required for simvastatin-induced up-regulation, because levels of an isoprenylation-deficient RhoB mutant were not affected by simvastatin. Moreover, this mutant was found to be markedly more stable than the wild-type protein. These results show that RhoB isoprenylation is necessary for rapid turnover of this protein and identify a novel link between the cholesterol biosynthetic pathway and the regulation of G-protein expression.
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Affiliation(s)
- Konstantinos Stamatakis
- Departamento de Estructura y Función de Proteinas, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Cientificas (C.S.I.C.), Velázquez, 144, 28006 Madrid, Spain
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Adnane J, Seijo E, Chen Z, Bizouarn F, Leal M, Sebti SM, Muñoz-Antonia T. RhoB, not RhoA, represses the transcription of the transforming growth factor beta type II receptor by a mechanism involving activator protein 1. J Biol Chem 2002; 277:8500-7. [PMID: 11741970 DOI: 10.1074/jbc.m104367200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
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.
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Affiliation(s)
- Jalila Adnane
- Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute, Department of Oncology, University of South Florida, Tampa, Florida 33612, USA
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Baron R, Fourcade E, Lajoie-Mazenc I, Allal C, Couderc B, Barbaras R, Favre G, Faye JC, Pradines A. RhoB prenylation is driven by the three carboxyl-terminal amino acids of the protein: evidenced in vivo by an anti-farnesyl cysteine antibody. Proc Natl Acad Sci U S A 2000; 97:11626-31. [PMID: 11027361 PMCID: PMC17251 DOI: 10.1073/pnas.97.21.11626] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protein isoprenylation is a lipid posttranslational modification required for the function of many proteins that share a carboxyl-terminal CAAX motif. The X residue determines which isoprenoid will be added to the cysteine. When X is a methionine or serine, the farnesyl-transferase transfers a farnesyl, and when X is a leucine or isoleucine, the geranygeranyl-transferase I, a geranylgeranyl group. But despite its CKVL motif, RhoB was reported to be both geranylgeranylated and farnesylated. Thus, the determinants of RhoB prenylation appear more complex than initially thought. To determine the role of RhoB CAAX motif, we designed RhoB mutants with modified CAAX sequence expressed in baculovirus-infected insect cells. We demonstrated that RhoB was prenylated as a function of the three terminal amino acids, i.e., RhoB bearing the CAIM motif of lamin B or CLLL motif of Rap1A was farnesylated or geranylgeranylated, respectively. Next, we produced a specific polyclonal antibody against farnesyl cysteine methyl ester allowing prenylation analysis avoiding the metabolic labeling restrictions. We confirmed that the unique modification of the RhoB CAAX box was sufficient to direct the RhoB distinct prenylation in mammalian cells and, inversely, that a RhoA-CKVL chimera could be alternatively prenylated. Moreover, the immunoprecipitation of endogenous RhoB from cells with the anti-farnesyl cysteine antibody suggested that wild-type RhoB is farnesylated in vivo. Taken together, our results demonstrated that the three last carboxyl amino acids are the main determinants for RhoB prenylation and described an anti-farnesyl cysteine antibody as a useful tool for understanding the cellular control of protein farnesylation.
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Affiliation(s)
- R Baron
- Endocrinologie et Communications Cellulaires Institut National de la Santé et de la Recherche Médicale Unité 397, Toulouse, France
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