Biomedical subjects

Claude Sardet

Publications and source records attributed to Claude Sardet.

5 recordsLinked to original sources

PubMed2002

Post-activation turn-off of NF-kappa B-dependent transcription is regulated by acetylation of p65.

NF-kappaB 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-kappaB is tightly regulated by its partner IkappaBalpha. Here, we show that the p65 subunit of NF-kappaB 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 kappaBeta-DNA. Finally, acetylation of p65 facilitated its removal from DNA and consequently its IkappaBetaalpha-mediated export from the nucleus. We propose that acetylation of p65 plays a key role in IkappaBetaalpha-mediated attenuation of NF-kappaBeta transcriptional activity which is an important process that restores the latent state in post-induced cells.

Acetylation↗

PubMed2002

A B-myb promoter corepressor site facilitates in vivo occupation of the adjacent E2F site by p107 x E2F and p130 x E2F complexes.

Transcription from the B-myb (MybL2 gene) promoter is strictly cell cycle-regulated by repression mediated through an E2F site during G(0)/early G(1). We report here the characterization of a corepressor site (downstream repression site (DRS)) required for this activity that is closely linked to the E2F site. Systematic mutagenesis of the DRS enabled a consensus to be derived, and it is notable that this sequence is compatible with cell cycle gene homology region sequences associated with cell cycle-dependent elements in the cyclin A, cdc2, and CDC25C promoters. The B-myb promoter is inappropriately active during G(0) in mouse embryo fibroblasts lacking the p107 and p130 pocket proteins, and we show that the ability of transfected p107 and p130 to re-impose repression on the promoter is dependent on the DRS. In contrast, transfected Rb was unable to repress the B-myb promoter. Consistent with the notion that Rb.E2F complexes are unable to bind the B-myb promoter E2F site in vivo, footprinting showed that this site is unoccupied in cells lacking p107 and p130. Chromatin immunoprecipitation assays showed a requirement for the DRS in recruiting p107 and p130 complexes to the B-myb promoter, indicating that in vivo the DRS governs the occupancy of the adjacent E2F site by transcriptional repressors.

3T3 Cells↗

PubMed2002

E2Fs regulate adipocyte differentiation.

When preadipocytes reenter the cell cycle, PPAR gamma expression is induced, coincident with an increase in DNA synthesis, suggesting the involvement of the E2F family of cell cycle regulators. We show here that E2F1 induces PPAR gamma transcription during clonal expansion, whereas E2F4 represses PPARg amma expression during terminal adipocyte differentiation. Using a combination of in vivo experiments with knockout and chimeric animals and in vitro experiments, we demonstrate that the absence of E2F1 impairs, whereas depletion of E2F4 stimulates, adipogenesis. E2Fs hence represent the link between proliferative signaling pathways, triggering clonal expansion, and terminal adipocyte differentiation through regulation of PPAR gamma expression. This underscores the complex role of the E2F protein family in the control of both cell proliferation and differentiation.

3T3 Cells↗

PubMed2002

Negative regulation of transcription by the type II arginine methyltransferase PRMT5.

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.

3T3 Cells↗

PubMed2002

Retinoblastoma protein transcriptional repression through histone deacetylation of a single nucleosome.

The retinoblastoma protein, pRb, controls transcription through recruitment of histone deacetylase to particular E2F-responsive genes. We determined the acetylation level of individual nucleosomes present in the cyclin E promoter of RB(+/+) and RB(-/-) mouse embryo fibroblasts. We also determined the effects of pRb on nucleosomal conformation by examining the thiol reactivity of histone H3 of individual nucleosomes. We found that pRb represses the cyclin E promoter through histone deacetylation of a single nucleosome, to which it and histone deacetylase 1 bind. In addition, the conformation of this nucleosome is modulated by pRb-directed histone deacetylase activity. Thus, the repressive role of pRb in cyclin E transcription and therefore cell cycle progression can be mapped to its control of the acetylation status and conformation of a single nucleosome.

Acetylation↗