RIP140 inhibits glycolysis-dependent proliferation of breast cancer cells by regulating GLUT3 expression through transcriptional crosstalk between hypoxia induced factor and p53.

Glycolysis is essential to support cancer cell proliferation, even in the presence of oxygen. The transcriptional co-regulator RIP140 represses the activity of transcription factors that drive cell proliferation and metabolism and plays a role in mammary tumorigenesis. Here we use cell proliferation and metabolic assays to demonstrate that RIP140-deficiency causes a glycolysis-dependent increase in breast tumor growth. We further demonstrate that RIP140 reduces the transcription of the glucose transporter GLUT3 gene, by inhibiting the transcriptional activity of hypoxia inducible factor HIF-2α in cooperation with p53. Interestingly, RIP140 expression was significantly associated with good prognosis only for breast cancer patients with tumors expressing low GLUT3, low HIF-2α and high p53, thus confirming the mechanism of RIP140 anti-tumor activity provided by our experimental data. Overall, our work establishes RIP140 as a critical modulator of the p53/HIF cross-talk to inhibit breast cancer cell glycolysis and proliferation.

The Prognostic Impact of the Aryl Hydrocarbon Receptor (AhR) in Primary Breast Cancer Depends on the Lymph Node Status.

Increasing evidence implicates the aryl hydrocarbon receptor (AhR) as a possible regulator of mammary carcinogenesis. This study aims to clarify its prognostic impact in breast cancer (BC). Meta-analyses performed at the mRNA level demonstrated that the predictive value of AhR expression in BC depends on the lymph node (LN) status. AhR expression and sub-cellular location were then analyzed by immunohistochemistry in 302 primary BC samples. AhR was expressed in almost 90% of cases with a predominant nuclear location. Nuclear and cytoplasmic AhR levels were significantly correlated and associated with the expression of RIP140 (receptor-interacting protein of 140 kDa), an AhR transcriptional coregulator and target gene. Interestingly, total and nuclear AhR levels were only significantly correlated with short overall survival in node-negative patients. In this sub-group, total and nuclear AhR expression had an even stronger prognostic impact in patients with low RIP140-expressing tumors. Very interestingly, the total AhR prognostic value was also significant in luminal-like BCs and was an independent prognostic marker for LN-negative patients. Altogether, this study suggests that AhR is a marker of poor prognosis for patients with LN-negative luminal-like BCs, which warrants further evaluation.

Prognostic relevance of RIP140 and ERß expression in unifocal versus multifocal breast cancers: a preliminary report.

The aim of this study was to investigate the expression of two nuclear receptor transcriptional coregulators, namely RIP140 (receptor-interacting protein of 140 kDa) and LCoR (ligand-dependent corepressor) in unifocal versus multifocal breast cancers. The expression of these two proteins was analyzed by immunohistochemistry in a matched-pair cohort of 21 unifocal and 21 multifocal breast tumors. The expression of the two estrogen receptors (ERα and ERß) was studied in parallel. RIP140 and LCoR levels appeared lower in unifocal tumors compared to multifocal samples (decreased of immune-reactive scores and reduced number of high expressing cells). In both tumor types, RIP140 and LCoR expression was correlated with each other and with expression of ERß. Very interestingly, the expression of RIP140, LCoR, and ERß was inversely correlated with overall survival only for the unifocal group. The negative correlation with overall and recurrence free survival was more pronounced in patients whose unifocal tumors expressed high levels of both RIP140 and ERß. Altogether, this preliminary report indicates that the ERß/RIP140 signaling is altered in unifocal breast cancers and correlated with patient outcome. Further investigation is needed to decipher the molecular mechanisms and the biological relevance of this deregulation.

The emerging role of the transcriptional coregulator RIP140 in solid tumors.

RIP140 is a transcriptional coregulator (also known as NRIP1) which plays very important physiological roles by finely tuning the activity of a large number of transcription factors. Noticeably, the RIP140 gene has been shown to be involved in the regulation of energy expenditure, in mammary gland development and intestinal homeostasis as well as in behavior and cognition. RIP140 is also involved in the regulation of various oncogenic signaling pathways and participates in the development and progression of solid tumors. This short review aims to summarize the role of this transcription factor on nuclear estrogen receptors, E2F and Wnt signaling pathways based on recent observations focusing on breast, ovary, liver and colon tumors.

RIP140 regulates transcription factor HES1 oscillatory expression and mitogenic activity in colon cancer cells.

The transcription factor receptor-interacting protein 140 (RIP140) regulates intestinal homeostasis and tumorigenesis through Wnt signaling. In this study, we investigated its effect on the Notch/HES1 signaling pathway. In colorectal cancer (CRC) cell lines, RIP140 positively regulated HES1 gene expression at the transcriptional level via a recombining binding protein suppressor of hairless (RBPJ)/neurogenic locus notch homolog protein 1 (NICD)-mediated mechanism. In support of these in vitro data, RIP140 and HES1 expression significantly correlated in mouse intestine and in a cohort of CRC samples, thus supporting the positive regulation of HES1 gene expression by RIP140. Interestingly, when the Notch pathway is fully activated, RIP140 exerted a strong inhibition of HES1 gene transcription controlled by the level of HES1 itself. Moreover, RIP140 directly interacts with HES1 and reversed its mitogenic activity in human CRC cells. In line with this observation, HES1 levels were associated with a better patient survival only when tumors expressed high levels of RIP140. Our data identify RIP140 as a key regulator of the Notch/HES1 signaling pathway, with a dual effect on HES1 gene expression at the transcriptional level and a strong impact on colon cancer cell proliferation.

[The Warburg effect: from theory to therapeutic applications in cancer]. / L'effet Warburg - De la théorie du cancer aux applications thérapeutiques en cancérologie.

Cancer cell metabolism described by Otto Warburg in the thirties became a cancer specific hallmark, also called "Warburg effect". Cancer cells use essentially glucose as fuel, through glycolysis, in order to meet their energy and biomass needs to insure their cell proliferation. Recent advances describe Warburg effect regulation by oncogenes and tumor suppressor genes. Moreover, mutations in some glycolysis enzymes are found in various cancers, highlighting the role of cell metabolism in cancer. In this review, we describe the mechanisms responsible for the Warburg effect at the molecular and cellular level, the role of cell signalling along with the implication of different transcription factors. As a cause or a consequence of tumorigenesis, the Warburg effect is now considered as a promising therapeutic target in the fight against cancer.

RIP140 regulates POLK gene expression and the response to alkylating drugs in colon cancer cells.

Aim: The transcription factor RIP140 (receptor interacting protein of 140 kDa) is involved in intestinal tumorigenesis. It plays a role in the control of microsatellite instability (MSI), through the regulation of MSH2 and MSH6 gene expression. The aim of this study was to explore its effect on the expression of POLK, the gene encoding the specialized translesion synthesis (TLS) DNA polymerase κ known to perform accurate DNA synthesis at microsatellites. Methods: Different mouse models and engineered human colorectal cancer (CRC) cell lines were used to analyze by RT-qPCR, while Western blotting and luciferase assays were used to elucidate the role of RIP140 on POLK gene expression. Published DNA microarray datasets were reanalyzed. The in vitro sensitivity of CRC cells to methyl methane sulfonate and cisplatin was determined. Results: RIP140 positively regulates, at the transcriptional level, the expression of the POLK gene, and this effect involves, at least partly, the p53 tumor suppressor. In different cohorts of CRC biopsies (with or without MSI), a strong positive correlation was observed between RIP140 and POLK gene expression. In connection with its effect on POLK levels and the TLS function of this polymerase, the cellular response to methyl methane sulfonate was increased in cells lacking the Rip140 gene. Finally, the association of RIP140 expression with better overall survival of CRC patients was observed only when the corresponding tumors exhibited low levels of POLK, thus strengthening the functional link between the two genes in human CRC. Conclusion: The regulation of POLK gene expression by RIP140 could thus contribute to the maintenance of microsatellite stability, and more generally to the control of genome integrity.

An R package for generic modular response analysis and its application to estrogen and retinoic acid receptor crosstalk.

Modular response analysis (MRA) is a widely used inference technique developed to uncover directions and strengths of connections in molecular networks under a steady-state condition by means of perturbation experiments. We devised several extensions of this methodology to search genomic data for new associations with a biological network inferred by MRA, to improve the predictive accuracy of MRA-inferred networks, and to estimate confidence intervals of MRA parameters from datasets with low numbers of replicates. The classical MRA computations and their extensions were implemented in a freely available R package called aiMeRA ( https://github.com/bioinfo-ircm/aiMeRA/ ). We illustrated the application of our package by assessing the crosstalk between estrogen and retinoic acid receptors, two nuclear receptors implicated in several hormone-driven cancers, such as breast cancer. Based on new data generated for this study, our analysis revealed potential cross-inhibition mediated by the shared corepressors NRIP1 and LCoR. We designed aiMeRA for non-specialists and to allow biologists to perform their own analyses.

A Truncated NRIP1 Mutant Amplifies Microsatellite Instability of Colorectal Cancer by Regulating MSH2/MSH6 Expression, and Is a Prognostic Marker of Stage III Tumors.

Microsatellite instability (MSI) is related to the alteration of mismatch repair (MMR) genes and plays a key role in colorectal cancer (CRC) pathogenesis. We previously reported that the transcription factor Nuclear Receptor Interacting Protein 1 (NRIP1) is involved in sporadic intestinal tumorigenesis. The aim of this study was to decipher its role in MSI CRC. By using different mouse models and engineered cell lines, we demonstrated that NRIP1 increased MSH2 and MSH6 MMR gene transcription and mRNA/protein levels. In human CRC cells, NRIP1 expression was associated with decreased MSI and the hypermutator phenotype, and with resistance to chemotherapy drugs. Using a cohort of 194 CRC patients, we detected in 22% of the cases a MSI-induced frameshift mutation in the NRIP1 coding sequence. This genetic alteration generates a truncated protein with a dominant negative activity that increased human CRC cell proliferation and impaired the regulation of MSH2 and MSH6 gene expression. Moreover, the NRIP1 mutant correlated with a decreased overall survival of patients with advanced CRC, especially when MLH1-deficient. By decreasing the expression of MSH2 and MSH6 gene expression, the NRIP1 variant may amplify MLH1-dependent CRC progression and behave as a new prognostic marker of advanced MSI CRC.

Estrogen receptor interactions and dynamics monitored in live cells by fluorescence cross-correlation spectroscopy.

Quantitative characterization of protein interactions in live cells remains one of the most important challenges in modern biology. In the present work we have used two-photon, two-color, fluorescence cross-correlation spectroscopy (FCCS) in transiently transfected COS-7 cells to measure the concentrations and interactions of estrogen receptor (ER) subtypes alpha and beta with one of their transcriptional coactivator proteins, TIF2, as well as heterodimerization between the two ER subtypes. Using this approach in a systematic fashion, we observed a strong ligand-dependent modulation of receptor-coactivator complexation, as well as strong protein concentration dependence for complex formation in the absence of ligand. These quantitative values for protein and complex concentrations provide the first estimates for the ER-TIF2 K(d) for the full-length proteins and in a cellular context (agonist, < approximately 6 nM; antagonist, > approximately 3 microM; unliganded, approximately 200 nM). Coexpression of the two ER subtypes revealed substantial receptor heterodimer formation. They also provide, for the first time, estimated homo- and heterodimerization constants found to be similar and in the low nanomolar range. These results underscore the importance of receptor and coregulator expression levels and stability in the tissue-dependent modulation of receptor function under normal and pathological conditions.

Importance of RIP140 and LCoR Sub-Cellular Localization for Their Association With Breast Cancer Aggressiveness and Patient Survival.

New markers are needed to improve diagnosis and to personalize treatments for patients with breast cancer (BC). Receptor-interacting protein of 140 kDa (RIP140) and ligand-dependent corepressor (LCoR), two transcriptional co-regulators of estrogen receptors, strongly interact in BC cells. Although their role in cancer progression has been outlined in the last few years, their function in BC has not been elucidated yet. In this study, we investigated RIP140 and LCoR localization (cytoplasm vs nucleus) in BC samples from a well-characterized cohort of patients (n = 320). RIP140 and LCoR were expressed in more than 80% of tumors, (predominantly in the cytoplasm), and the two markers were highly correlated. Expression of RIP140 and LCoR in the nucleus was negatively correlated with tumor size. Conversely, RIP140 and LCoR cytoplasmic expression strongly correlated with expression of two tumor aggressiveness markers: N-cadherin and CD133 (epithelial mesenchymal transition and cancer stem cell markers, respectively). Finally, high RIP140 nuclear expression was significantly correlated with longer overall survival, whereas high total or cytoplasmic expression of RIP140 was associated with shorter disease-free survival. Our study strongly suggests that the role of RIP140 and LCoR in BC progression could vary according to their prevalent sub-cellular localization, with opposite prognostic values for nuclear and cytoplasmic expression. The involvement in BC progression/invasiveness of cytoplasmic RIP140 could be balanced by the anti-tumor action of nuclear RIP140, thus explaining the previous contradictory findings about its role in BC.

Receptor-interacting protein 140 differentially regulates estrogen receptor-related receptor transactivation depending on target genes.

We have investigated the effects of receptor-interacting protein 140 (RIP140) on transcriptional regulation by estrogen receptor-related receptors (ERRs). We first show that RIP140 inhibits transactivation by ERRalpha, beta, and gamma on natural or artificial reporter genes containing different types of response elements. This repression correlates with a strong in vitro binding between several regions of RIP140 and the three ERR isoforms. Surprisingly, although RIP140 inhibits transactivation of the thyroid hormone receptor-alpha gene by ERRbeta, it significantly increases its regulation by ERRalpha and ERRgamma. Mutagenesis and transient transfections in SL2 cells indicate that thyroid hormone receptor-alpha promoter expression involved Sp1 sites. In support of this observation, we demonstrate that RIP140 also positively regulates ERRs transactivation of other known Sp1 targets such as the p21 gene. This effect requires the two proximal Sp1 binding sites of the promoter and is partially dependent on the activation function 2 domain of ERRs. Finally, we provide evidences for a role of histone deacetylases in the regulation of p21 promoter by RIP140. Altogether, these data indicate that RIP140 differentially regulates ERR activity depending on the target sequence on the promoters.

Receptor-interacting protein 140 is a repressor of the androgen receptor activity.

The androgen receptor (AR) is a ligand-activated transcription factor that controls growth and survival of prostate cancer cells. In the present study, we investigated the regulation of AR activity by the receptor-interacting protein 140 (RIP140). We first showed that RIP140 could be coimmunoprecipitated with the receptor when coexpressed in 293T cells. This interaction appeared physiologically relevant because chromatin immunoprecipitation assays revealed that, under R1881 treatment, RIP140 could be recruited to the prostate-specific antigen encoding gene in LNCaP cells. In vitro glutathione S-transferase pull-down assays provided evidence that the carboxy-terminal domain of AR could interact with different regions of RIP140. By means of fluorescent proteins, we demonstrated that ligand-activated AR was not only able to translocate to the nucleus but also to relocate RIP140 from very structured nuclear foci to a diffuse pattern. Overexpression of RIP140 strongly repressed AR-dependent transactivation by preferentially targeting the ligand binding domain-dependent activity. Moreover, disruption of RIP140 expression induced AR overactivation, thus revealing RIP140 as a strong AR repressor. We analyzed its mechanism of transrepression and first demonstrated that different regions of RIP140 could mediate AR-dependent repression. We then showed that the carboxy-terminal end of RIP140 could reverse transcriptional intermediary factor 2-dependent overactivation of AR. The use of mutants of RIP140 allowed us to suggest that C-terminal binding protein played no role in RIP140-dependent inhibition of AR activity, whereas histone deacetylases partly regulated that transrepression. Finally, we provided evidence for a stimulation of RIP140 mRNA expression in LNCaP cells under androgen treatment, further emphasizing the role of RIP140 in androgen signaling.

Negative regulation of hormone signaling by RIP140.

Receptor interacting protein (RIP) 140 is a negative transcriptional regulator of nuclear hormone receptors which is required for the maintenance of energy homeostasis and ovulation. Despite its recruitment by agonist-liganded receptors, this protein exhibits a strong repressive activity which was initially attributed to competition with coactivator binding on nuclear receptors. However, RIP140 also exerts active repression implicating the Carboxyl-terminal binding proteins (CtBPs) and histone deacetylases (HDACs). We recently demonstrated that the Carboxyl-terminal region of the molecule contains two additional silencing domains which require post-translational modifications to be fully active. In human breast cancer cells, RIP140 expression is up-regulated at the transcriptional level by various ligands of nuclear receptors. We have recently cloned the human RIP140 gene and defined the mechanism of its regulation by estrogens. In order to better characterize the role of RIP140 in hormone signaling, we have studied its interaction with the androgen receptor and demonstrated its ability to repress transcriptional regulation by androgens. RIP140 also inhibits transactivation by estrogen receptor-related receptors (ERRalpha, beta and gamma) on natural or artificial reporter genes containing different types of response elements. Surprisingly, RIP140 positively regulates ERR transactivation when the receptors are recruited to target promoters through interaction with the Sp1 transcription factor and this effect could involve titration of histone deacetylases. Altogether, these results underline that transcriptional regulation of hormone signaling by the cofactor RIP140 involves complex mechanisms relying on multiple domains and partners.

Multiple domains of the Receptor-Interacting Protein 140 contribute to transcription inhibition.

In this study, we have investigated the role of C-terminal binding proteins (CtBPs) and histone deacetylases (HDACs) in the repressive activity of the nuclear receptor cofactor Receptor-Interacting Protein 140 (RIP140). We have defined the interaction of both CtBP1 and CtBP2 with RIP140 and delineated two motifs (PIDLS and PINLS) differentially required for in vitro interaction. Using different approaches (titration of endogenous CtBPs, mutagenesis and transfection in CtBP knock-out cells), we find that recruitment of CtBPs only partially explains the negative regulation exerted by RIP140. We then demonstrate that RIP140 associates in vitro not only with class I HDACs but also with class II enzymes such as HDAC5. This interaction mainly involves the N-terminus of RIP140 (residues 27-199) and two domains of HDAC5. Moreover, the two proteins functionally interfere in transfection experiments, and confocal microscopy indicates that they co-localize in the nucleus. Interestingly, using the specific HDAC inhibitor trichostatin A, we show that HDAC activity is dispensable for active transrepression by RIP140. Finally, we demonstrate that the C-terminal region of RIP140 contains two additional silencing domains and confers strong active transrepression independently of HDAC activity and CtBPs. Altogether, these data indicate that transcriptional inhibition by the cofactor RIP140 involves complex mechanisms relying on multiple domains and partners.

Histone deacetylase 9 regulates breast cancer cell proliferation and the response to histone deacetylase inhibitors.

Histone lysine acetylation is an epigenetic mark regulated by histone acetyltransferases and histone deacetylases (HDAC) which plays an important role in tumorigenesis. In this study, we observed a strong overexpression of class IIa HDAC9, at the mRNA and protein levels, in the most aggressive human breast cancer cell lines (i.e. in basal breast cancer cells vs luminal ones or in malignant vs begnin MCF10A breast epithelial cell lines). HDAC9 overexpression was associated with higher rates of gene transcription and increased epigenetic marks on the HDAC9 promoter. Ectopic expression of HDAC9 in MCF7 luminal breast cancer cells led to an increase in cell proliferation and to a decrease in apoptosis. These effects were associated with a deregulated expression of several genes controlled by HDAC inhibitors such as CDKN1A, BAX and TNFRSF10A. Inversely, knock-down of HDAC9 expression in MDA-MB436 basal breast cancer cells reduced cell proliferation. Moreover, high HDAC9 expression decreased the efficacy of HDAC inhibitors to reduce cell proliferation and to regulate CDKN1A gene expression. Interestingly, the gene encoding the transcription factor SOX9 was identified by a global transcriptomic approach as an HDAC9 target gene. In stably transfected MCF7 cells, SOX9 silencing significantly decreased HDAC9 mitogenic activity. Finally, in a large panel of breast cancer biopsies, HDAC9 expression was significantly increased in tumors of the basal subtype, correlated with SOX9 expression and associated with poor prognosis. Altogether, these results indicate that HDAC9 is a key factor involved in mammary carcinogenesis and in the response to HDAC inhibitors.

[RIP140 and hormone signaling]. / Rôle de RIP140 dans la signalisation hormonale.

Nuclear hormone receptors belong to a superfamily of ligand-activated transcription factors which regulate fundamental physiological processes. Their activity is controlled by a large number of coregulatory proteins which are, in most cases, recruited by nuclear receptors in the presence of ligand. RIP140 (receptor interacting protein of 140 kDa) was one of the first transcription cofactors to be identified almost ten years ago. This molecule is an atypical cofactor which interacts with agonist-liganded nuclear receptors but negatively regulates their transactivation potential. RIP140 exhibits nine leucine-rich motifs (LxxLL) which mediate the specific docking on the nuclear receptor ligand-binding domain. Transcription repression exerted by this cofactor implicates different mechanisms. Not only it involves a competition with coactivators such as those belonging to the p160 family, but also relies on active intrinsic repression through at least four different domains which allow recruitement of downstream repressors such as histone deacetylases (HDACs) or C-terminal binding proteins (CtBPs). The biological role of RIP140 has been investigated by disrupting the gene in mice. The lack of RIP140 expression in ovaries prevents follicle rupture and ovulation, rising to female infertility. In addition, this cofactor is also required for the control of fat storage and utilization through the regulation of genes involved in thermogenesis. Finally, RIP140 could play a role in the hormonal control of cancer cell proliferation by negatively regulating the activity of estrogen and retinoic acid receptors which are key actors in cancer growth. Interestingly, both estrogens and retinoic acid regulate RIP140 gene expression, revealing an increased level of complexity. In conclusion, RIP140 is an atypical transcription inhibitor which, by repressing nuclear hormone receptor activity, plays fundamental physiopathological roles.

Expression and role of RIP140/NRIP1 in chronic lymphocytic leukemia.

RIP140 is a transcriptional coregulator, (also known as NRIP1), which finely tunes the activity of various transcription factors and plays very important physiological roles. Noticeably, the RIP140 gene has been implicated in the control of energy expenditure, behavior, cognition, mammary gland development and intestinal homeostasis. RIP140 is also involved in the regulation of various oncogenic signaling pathways and participates in the development and progression of solid tumors. During the past years, several papers have reported evidences linking RIP140 to hematologic malignancies. Among them, two recent studies with correlative data suggested that gene expression signatures including RIP140 can predict survival in chronic lymphocytic leukemia (CLL). This review aims to summarize the literature dealing with the expression of RIP140 in CLL and to explore the potential impact of this factor on transcription pathways which play key roles in this pathology.

Transcriptional repression of estrogen receptor α signaling by SENP2 in breast cancer cells.

Estrogen receptors (ERs) are ligand-activated transcription factors involved in many physiological and pathological processes, including breast cancer. Their activity is fine-tuned by posttranslational modifications, notably sumoylation. In the present study, we investigated the role of the small ubiquitin-related modifier (SUMO) protease, SUMO1/sentrin/suppressor of Mif 2-specific peptidase 2 (SENP2), in the regulation of ERα activity. We first found SENP2 to significantly repress estradiol-induced transcriptional activity in breast cancer cells (MCF7 and T47D). This effect was observed with a reporter plasmid and on endogenous genes such as TFF1 and CTSD, which were shown to recruit SENP2 in chromatin immunoprecipitation experiments. Using glutathione S-transferase pull-down, coimmunoprecipitation and proximity ligation assays, SENP2 was found to interact with ERα and this interaction to be mediated by the amino-terminal region of the protease and the hinge region of the receptor. Interestingly, we demonstrated that ERα repression by SENP2 is independent of its SUMO protease activity and requires a transcriptional repressive domain located in the amino-terminal end of the protease. Using small interfering RNA assays, we evidenced that this domain recruits the histone deacetylase 3 (HDAC3), to be fully active. Furthermore, using both overexpression and knockdown strategies, we showed that SENP2 robustly represses estrogen-dependent and independent proliferation of MCF7 cells. We provided evidence that this effect requires both the proteolytic and transcriptional activities of SENP2. Altogether, our study unravels a new property for a SUMO protease and identifies SENP2 as a classical transcription coregulator.

RIP140 increases APC expression and controls intestinal homeostasis and tumorigenesis.

Deregulation of the Wnt/APC/ß-catenin signaling pathway is an important consequence of tumor suppressor APC dysfunction. Genetic and molecular data have established that disruption of this pathway contributes to the development of colorectal cancer. Here, we demonstrate that the transcriptional coregulator RIP140 regulates intestinal homeostasis and tumorigenesis. Using Rip140-null mice and mice overexpressing human RIP140, we found that RIP140 inhibited intestinal epithelial cell proliferation and apoptosis. Interestingly, following whole-body irradiation, mice lacking RIP140 exhibited improved regenerative capacity in the intestine, while mice overexpressing RIP140 displayed reduced recovery. Enhanced RIP140 expression strongly repressed human colon cancer cell proliferation in vitro and after grafting onto nude mice. Moreover, in murine tissues and human cancer cells, RIP140 stimulated APC transcription and inhibited ß-catenin activation and target gene expression. Finally, RIP140 mRNA and RIP140 protein levels were decreased in human colon cancers compared with those in normal mucosal tissue, and low levels of RIP140 expression in adenocarcinomas from patients correlated with poor prognosis. Together, these results support a tumor suppressor role for RIP140 in colon cancer.