[Show abstract][Hide abstract] ABSTRACT: Protein arginine methyltransferase 5 (PRMT5) targets nuclear and cytoplasmic proteins. Here, we identified a nuclear protein, called cooperator of PRMT5 (COPR5), involved in the nuclear functions of PRMT5. COPR5 tightly binds to PRMT5, both in vitro and in living cells, but not to other members of the PRMT family. PRMT5 bound to COPR5 methylates histone H4 (R3) preferentially when compared with histone H3 (R8), suggesting that COPR5 modulates the substrate specificity of nuclear PRMT5-containing complexes, at least towards histones. Markedly, recombinant COPR5 binds to the amino terminus of histone H4 and is required to recruit PRMT5 to reconstituted nucleosomes in vitro. Consistently, COPR5 depletion in cells strongly reduces PRMT5 recruitment on chromatin at the PRMT5 target gene cyclin E1 (CCNE1) in vivo. Moreover, both COPR5 depletion and overexpression affect CCNE1 promoter expression. We propose that COPR5 is an important chromatin adaptor for PRMT5 to function on a subset of its target genes.
[Show abstract][Hide abstract] ABSTRACT: The Cyclin E1 gene (CCNE1) is an ideal model to explore the mechanisms that control the transcription of cell cycle-regulated genes whose expression rises transiently before entry into S phase. E2F-dependent regulation of the CCNE1 promoter was shown to correlate with changes in the level of H3-K9 acetylation/methylation of nucleosomal histones positioned at the transcriptional start site region. Here we show that, upon growth stimulation, the same region is subject to variations of H3-R17 and H3-R26 methylation that correlate with the recruitment of coactivator-associated arginine methyltransferase 1 (CARM1) onto the CCNE1 and DHFR promoters. Accordingly, CARM1-deficient cells lack these modifications and present lowered levels and altered kinetics of CCNE1 and DHFR mRNA expression. Consistently, reporter gene assays demonstrate that CARM1 functions as a transcriptional coactivator for their E2F1/DP1-stimulated expression. CARM1 recruitment at the CCNE1 gene requires activator E2Fs and ACTR, a member of the p160 coactivator family that is frequently overexpressed in human breast cancer. Finally, we show that grade-3 breast tumors present coelevated mRNA levels of ACTR and CARM1, along with their transcriptional target CCNE1. All together, our results indicate that CARM1 is an important regulator of the CCNE1 gene.
Proceedings of the National Academy of Sciences 10/2006; 103(36):13351-6. DOI:10.1073/pnas.0605692103 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The helix-loop-helix transcription factor TFE3 has been suggested to play a role in the control of cell growth by acting as a binding partner of transcriptional regulators such as E2F3, SMAD3, and LEF-1. Furthermore, translocations/TFE3 fusions have been directly implicated in tumorigenesis. Surprisingly, however, a direct functional role for TFE3 in the regulation of proliferation has not been reported. By screening retroviral cDNA expression libraries to identify cDNAs that confer resistance to a pRB-induced proliferation arrest, we have found that TFE3 overrides a growth arrest in Rat1 cells induced by pRB and its upstream regulator p16(INK4A). In addition, TFE3 expression blocks the anti-mitogenic effects of TGF-beta in rodent and human cells. We provide data supporting a role for endogenous TFE3 in the direct regulation of CYCLIN E expression in an E2F3-dependent manner. These observations establish TFE3 as a functional regulator of proliferation and offer a potential mechanism for its involvement in cancer.
[Show abstract][Hide abstract] ABSTRACT: Resistance to 4-hydroxy-tamoxifen (OHT), which appears in breast cancer cells after long-term antiestrogen treatment, may involve irreversible changes of gene expression. We previously developed a MCF-7 derived cell line (MVLN), in which OHT rapidly and irreversibly inactivates the expression of an estrogen-regulated luciferase transgene (Vit-tk-luciferase). In chromatin immunoprecipitation experiments, heterochromatin protein 1 (HP1alpha) was found to be associated with the Vit-tk-luciferase transgene, only when it was inactivated by OHT treatment. Chimeras composed of either HP1alpha or the Krupple-associated box (KRAB) module of KOX-1 protein (known to repress gene expression by recruitment of HP1 proteins), fused to the estrogen receptor (ER)-DNA binding domain (DBD) and the androgen receptor (AR)-ligand binding domain (LBD) were generated and appeared as potent transcriptional repressors. In stably transfected MVLN cells, irreversible inactivation of the luciferase transgene expression obtained with HP1alpha-ER(DBD)-AR(LBD) was partial, whereas inactivation obtained with KRAB-ER(DBD)-AR(LBD) was comparable to that obtained with OHT, although with a slower kinetics. Altogether, these data suggest that HP1alpha is involved in the silencing effects associated with long-term OHT treatments.
[Show abstract][Hide abstract] ABSTRACT: NF-κB represents a family of eukaryotic transcription factors participating in the regulation of various cellular genes involved
in the immediate early processes of immune, acute-phase, and inflammatory responses. Cellular localization and consequently
the transcriptional activity of NF-κB is tightly regulated by its partner IκBα. Here, we show that the p65 subunit of NF-κB
is acetylated by both p300 and PCAF on lysines 122 and 123. Both HDAC2 and HDAC3 interact with p65, although only HDAC3 was
able to deacetylate p65. Acetylation of p65 reduces its ability to bind κΒ-DNA. Finally, acetylation of p65 facilitated its
removal from DNA and consequently its IκΒα-mediated export from the nucleus. We propose that acetylation of p65 plays a key
role in IκΒα-mediated attenuation of NF-κΒ transcriptional activity which is an important process that restores the latent
state in post-induced cells.
[Show abstract][Hide abstract] ABSTRACT: We have identified previously a repressor element in the transcription start site region of the cyclin E1 promoter that periodically associates with an atypical, high molecular weight E2F complex, termed CERC. Purification of native CERC reveals the presence of the type II arginine methyltransferase PRMT5, which can mono- or symetrically dimethylate arginine residues in proteins. Chromatin immunoprecipitations (ChIPs) show that PRMT5 is associated specifically with the transcription start site region of the cyclin E1 promoter. ChIP analyses also show that this correlates with the presence on the same promoter region of arginine-methylated proteins including histone H4, an in vitro substrate of PRMT5. Consistent with its presence within the repressor complex, forced expression of PRMT5 negatively affects cyclin E1 promoter activity and cellular proliferation, effects that require its methyltransferase activity. These data provide the first direct experimental evidence that a type II arginine methylase is involved in the control of transcription and proliferation.