Project description:Recent genetic studies in mice have established a key role for the nuclear receptor coregulator Trim24 in liver tumor suppression and provided evidence that Trim24 suppresses hepatocarcinogenesis by inhibiting retinoic acid receptor alpha (Rara)-dependent transcription and cell proliferation. However, it is unknown which downstream targets of Rara regulated by Trim24 are critical for tumorigenesis. We report here that loss of Trim24 results in the overexpression of interferon (IFN)/STAT pathway genes in the liver, a process that occurs early in tumorigenesis and is more pronounced in tumors, despite the enhanced expression, late in the disease, of negative regulators such as Usp18, Socs1 and Socs2. Remarkably, Rara haplodeficiency, which was previously shown to suppress tumor development in Trim24-/- mice, also suppresses overexpression of the IFN/STAT pathway, thus providing evidence for a cross-pathway control that may be relevant to the transformation process. Biochemical studies revealed that Trim24 binds to the retinoic acid (RA)-responsive element in the Stat1 promoter in a RA-dependent manner and represses RA-induced transcription from this promoter. Together, these results identify Trim24 as a novel regulator of the IFN/STAT pathway and indicate that Trim24-mediated repression of the IFN/STAT signaling through Rara inhibition may play a critical role in preventing liver cancer. Generation of Trim24-/- mice has been described previously (Khetchoumian et al., 2007) by gene disruption. To generate compound mutant mice with a single allele of Rara deleted in the Trim24 -/- mutant background, we crossed Trim24 -/- mice with Rara+/- mice. The resulting Trim24+/- Rara+/- mice were generated in the hybrid (C57BL/6 (60%), 129/Sv (40%)) genetic background. These double heterozygous Trim24+/- Rara+/- mice were intercrossed to generate Trim24 -/-, Trim24 -/- Rara+/- and wild-type mice. Transcriptional profiling of mice at 5-weeks and 14-weeks of age.

Project description:The aim of this study is to identify microRNAs (miRNAs) transcriptionnally regulated by retinoic acid (RA). For that purpose we have used the RA-based treatment of the Acute Promyelocytic Leukemia (APL) as a model. This malignancy is characterised by a differentiation arrest of granulopoiesis at the promyelocytic stage. APL is molecularly associated with reciprocal translocations that always involve the retinoic acid receptor a (RARa). In the vast majority of APL cases, a t(15;17) chromosomal translocation fuses the genes encoding the promyelocytic leukemia protein PML and RARa. The resulting PML-RARa is a transcriptional repressor that impedes the expression of RA-regulated genes notably through an aberrant recruitment of transcriptional repressors and histone deacetylases. Consequently, these genes become insensitive to physiological doses (nanoM) of all-trans-retinoic acid (ATRA) but pharmacological doses (microM), overcome the PML-RARa-mediated repression and restore normal transcription and granulocytic differentiation. The restorative effects of RA can be reproduced in vitro in the NB4 cells, which were derived from an APL patient. These cells provide an excellent model to study the transcriptional deregulations that arise in APL and the molecular effects of the anti-cancerous RA-based treatment. We also used in this study the RA-resistant cells, namely NB4-LR1 and NB4-LR2 cells. The NB4-LR1 cells do transcriptionally respond to ATRA but do not maturate. In contrast, the NB4-LR2 cells show a clear defect in RA signaling, as they harbor a truncated form of PML-RAR protein that is not sensitive to pharmacological doses of RA. First, we plan to characterize miRNAs-repressed by PML-RAR. We reasoned that if some miRNAs are repressed by this protein, then pharmacological doses of RA should abolish this repression and lead to an increase in the level of expression of the corresponding miRNAs. NB4, NB4-LR1 and NB4-LR2 cells will thus be treated for 16h with ATRA (1 microM), and miRNAs profiles will be compared. We anticipate that, the expression of a potential miRNA-repressed by PML-RAR should be up-regulated by ATRA in both NB4 and NB4-LR1 cells but remain unchanged in NB4-LR2 cells. This expression pattern should in fact be similar to those observed for known RA-regulated genes, such as RARb, a well characterized target of the RARa and PML-RAR proteins. Importantly, this experimental procedure was already validated with the identification of a miRNA repressed by PML-RAR (patent Lecellier et al. #WO 2006/048553). MiRNAs candidates obtained will then be validated by chromatin immunoprecipitation using anti-RARa and anti-PML antibodies, followed by luciferase assays in presence or absence of ATRA. Keywords: retinoic acid-mediated gene regulation To characterize miRNAs regulated by PML-RAR.

Project description:The aim of this study is to identify microRNAs (miRNAs) transcriptionnally regulated by retinoic acid (RA). For that purpose we have used the RA-based treatment of the Acute Promyelocytic Leukemia (APL) as a model. This malignancy is characterised by a differentiation arrest of granulopoiesis at the promyelocytic stage. APL is molecularly associated with reciprocal translocations that always involve the retinoic acid receptor a (RARa). In the vast majority of APL cases, a t(15;17) chromosomal translocation fuses the genes encoding the promyelocytic leukemia protein PML and RARa. The resulting PML-RARa is a transcriptional repressor that impedes the expression of RA-regulated genes notably through an aberrant recruitment of transcriptional repressors and histone deacetylases. Consequently, these genes become insensitive to physiological doses (nanoM) of all-trans-retinoic acid (ATRA) but pharmacological doses (microM), overcome the PML-RARa-mediated repression and restore normal transcription and granulocytic differentiation. The restorative effects of RA can be reproduced in vitro in the NB4 cells, which were derived from an APL patient. These cells provide an excellent model to study the transcriptional deregulations that arise in APL and the molecular effects of the anti-cancerous RA-based treatment. We also used in this study the RA-resistant cells, namely NB4-LR1 and NB4-LR2 cells. The NB4-LR1 cells do transcriptionally respond to ATRA but do not maturate. In contrast, the NB4-LR2 cells show a clear defect in RA signaling, as they harbor a truncated form of PML-RAR protein that is not sensitive to pharmacological doses of RA. First, we plan to characterize miRNAs-repressed by PML-RAR. We reasoned that if some miRNAs are repressed by this protein, then pharmacological doses of RA should abolish this repression and lead to an increase in the level of expression of the corresponding miRNAs. NB4, NB4-LR1 and NB4-LR2 cells will thus be treated for 16h with ATRA (1 microM), and miRNAs profiles will be compared. We anticipate that, the expression of a potential miRNA-repressed by PML-RAR should be up-regulated by ATRA in both NB4 and NB4-LR1 cells but remain unchanged in NB4-LR2 cells. This expression pattern should in fact be similar to those observed for known RA-regulated genes, such as RARb, a well characterized target of the RARa and PML-RAR proteins. Importantly, this experimental procedure was already validated with the identification of a miRNA repressed by PML-RAR (patent Lecellier et al. #WO 2006/048553). MiRNAs candidates obtained will then be validated by chromatin immunoprecipitation using anti-RARa and anti-PML antibodies, followed by luciferase assays in presence or absence of ATRA. Keywords: retinoic acid-mediated gene regulation

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Negative regulation of the IFN/STAT signaling pathway by the Trim24 tumor suppressor protein through Rara inhibition

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