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Small ubiquitin-like modifier (SUMO) modification is emerging as an important control in transcription regulation. Here, we show that CREB-binding protein (CBP), a versatile transcriptional coactivator for numerous transcription factors in response to diverse signaling events, can be modified by SUMO-1 at lysine residues 999, 1034, and 1057 both in vitro and in vivo. Mutation of the SUMO acceptor lysine residues either individually or in combination enhanced CBP transcriptional activity, and expression of a SUMO protease SENP2 potentiated the transcriptional activity of CBP wild-type but not its sumoylation mutant, indicating that SUMO modification negatively regulates CBP transcriptional activity. Furthermore, we demonstrated an interaction of SUMO-1-modified CBP with the transcriptional corepressor Daxx and an essential role of Daxx in mediating SUMO-dependent transcriptional regulation of CBP through histone deacetylase 2 recruitment. Together, our findings indicate that SUMO modification and subsequent recruitment of Daxx represent a previously undescribed mechanism in modulating CBP transcriptional potential. protein-protein interaction | posttranslational modification | transcriptional repression | SENP2 | histone deacetylase 2

Research has been conducted on histone posttranslational modification. The role of KAP-1 corepressor in the KRAB-ZFP transcriptional silencer superfamily has been investigated and the results indicate that this corepressor binds to SETDB1, a SET domain protein with histone H3-K9-specific methyltransferase activity.

Large germinal vesicles (GV) are found in surf clam Spisula solidissima oocytes which are arrested during meiotic prophase I at the G2/M boundary. The large (GV) occupy 25% of the oocyte volume which has messenger RNAs and proteins which increase the rate of cell division during early cell development phase. The 49 kilo dalton phosphoprotein which is involved in the large GVs is characterized and isolated.

The promyelocyte-retinoic acid receptor (PML-RAR-alpha) protein is possibly a dominant negative oncogene that targets a nuclear matrix-associated structure. PML-RAR inhibits the formation of structures that are designated PML oncogenic domains (POD). Immunohistochemical and functional techniques reveal that PML-RAR forms heterodimers and is localized in the nucleus of leukemic cells. PML-RAR oncoprotein expression disrupts POD in acute promyelocytic leukemia cells.

Research has been conducted on heterochromodomain protein 1 which is required for stable epigenetic gene silencing. The authors report that the recruitment of mammalian heterochromodomain protein 1 to the euchromatic promoter establishes the epigenetically heritable silenced state.

PML gene was discovered as a fusion partner with retinoic acid receptor (RAR) a in the t(15:17) chromosomal translocation associated with acute promyelocytic leukemia (APL). Nuclear PML protein has been implicated in cell growth, tumor suppression, apoptosis, transcriptional regulation, chromatin remodeling, DNA repair, and anti-viral defense. The localization pattern of promyelocytic leukemia (PML) protein is drastically altered during viral infection. This alteration is traditionally viewed as a viral strategy to promote viral replication. Although multiple PML splice variants exist, we demonstrate that the ratio of a subset of cytoplasmic PML isoforms lacking exons 5 & 6 is enriched in cells exposed to herpes simplex virus-1 (HSV-1). In particular, we demonstrate that a PML isoform lacking exons 5 & 6, called PML Ib, mediates the intrinsic cellular defense against HSV-1 via the cytoplasmic sequestration of the infected cell protein (ICP) 0 of HSV-1. The results herein highlight the importance of cytoplasmic PML and call for an alternative, although not necessarily exclusive, interpretation regarding the redistribution of PML that is seen in virally infected cells. [ABSTRACT FROM AUTHOR]

Small ubiquitin-like modifier (SUMO) modification is emerging as an important control in transcription regulation. Here, we show that CREB-binding protein (CBP), a versatile transcriptional coactivator for numerous transcription factors in response to diverse signaling events, can be modified by SUMO-1 at lysine residues 999, 1034, and 1057 both in vitro and in viva Mutation of the SUMO acceptor lysine residues either individually or in combination enhanced CBP transcriptional activity, and expression of a SUMO protease SENP2 potentiated the transcriptional activity of CBP wild-type but not its sumoylation mutant, indicating that SUMO modification negatively regulates CBP transcriptional activity. Furthermore, we demonstrated an interaction of SUMO-1- modified CBP with the transcriptional corepressor Daxx and an essential role of Daxx in mediating SUMO-dependent transcriptional regulation of CBP through histone deacetylase 2 recruitment. Together, our findings indicate that SUMO modification and subsequent recruitment of Daxx represent a previously undescribed mechanism in modulating CBP transcriptional potential. [ABSTRACT FROM AUTHOR]

Placing regulatory proteins into different multiprotein complexes should modify key cellular processes. Here, we show that the transcription repressor Daxx and the SWI/SNF protein ATRX are both associated with two intranuclear domains: ND10/PML bodies and heterochromatin. The accumulation of ATRX at nuclear domain 10 (ND10) was mediated by its interaction with the N-terminus of Daxx. Binding of this complex to ND10 was facilitated by the interaction of the Daxx C-terminus with SUMOylated promyelocytic leukemia protein (PML). Although ATRX was present at heterochromatin during the entire cell cycle, Daxx was actively recruited to this domain at the end of S-phase. The FACT-complex member structure-specific recognition protein 1 (SSRP1) accumulated at heterochromatin simultaneously with Daxx and accumulation of both proteins depended on ATRX phosphorylation. Both Daxx and SSRP1 were released from heterochromatin early in G2 phase and Daxx was recruited back to ND10, indicating that both proteins localize to heterochromatin during a very short temporal window of the cell cycle. ATRX seems to assemble a repression multiprotein complex including Daxx and SSRP1 at heterochromatin during a specific stage of the cell cycle, whereas Daxx functions as an adapter for ATRX accumulation at ND10. A potential functional consequence of Daxx accumulation at heterochromatin was found in the S- to G2-phase transition. In Daxx-/- cells, S-phase was accelerated and the propensity to form double nuclei was increased, functional changes that could be rescued by Daxx reconstitution and that might be the basis for the developmental problems observed in Daxx knockout animals. [ABSTRACT FROM AUTHOR]

Herpesviruses start their transcriptional cascade at nuclear domain 10 (ND10). The deposition of virus genomes at these nuclear sites occurs due to the binding of the interferon-inducible repressor protein promyelocytic leukemia protein (PML) and/or Daxx to a viral DNA-protein complex. However, the presence of repressive proteins at the nuclear site of virus transcription has remained unexplained. We investigated the mouse cytomegalovirus (MCMV) immediate-early 1 protein (IE1), which is necessary for productive infection at low multiplicities of infection and therefore likely to be involved in overcoming cellular repression. Temporal analysis of IE1 distribution revealed its initial segregation into ND10 by binding to PML and/or Daxx and IE1-dependent recruitment of the transcriptional repressor histone deacetylase-2 (HDAC-2) to this site. However, these protein aggregates are dissociated in cells producing sufficient IE1 through titration of PML, Daxx, and HDAC-2. Importantly, binding of IE1 to HDAC-2 decreased deacetylation activity. Moreover, inhibition of HDAC by trichostatin-A resulted in an increase in viral protein synthesis, an increase in cells starting the formation of prereplication compartments, and an increase in the total infectious viruses produced. Thus, IE1, like trichostatin-A, reverses the repressive effect of HDAC evident in the presence of acetylated histones in the immediate-early promoter region. Since HDAC also binds to the promoter region of IE1, as determined by the chromatin immunoprecipitation assay, these combined results suggest that IE1 inhibits or reverses HDAC-mediated repression of the infecting viral genomes, possibly by a process akin to activation of heterochromatin. We propose that even permissive cells can repress transcription of infecting viral genomes through repressors, including HDAC, Daxx, and PML, and the segregation of IE1 to ND10 that would inactivate those repressors. The virus can counter this repression by... [ABSTRACT FROM AUTHOR]

Daxx has been implicated in the regulation of c-Jun N-terminus Kinase (JNK) activity and apoptosis, however, data on Daxx effect on apoptosis are controversial. According to many reports, Daxx participates in activation of JNK and acts as a proapoptotic protein, while others state that Daxx may block activation of JNK and apoptosis. In this study, we investigated hydrogen peroxide-mediated JNK activation and its dependence on the expression level of Daxx protein. Our data show that Daxx overexpression does not effect JNK activation. We have also found that cell lines generated from Daxx gene knockout mice are still capable to respond to H2O2 treatment by JNK activation. Reconstitution of wild type Daxx protein expression in Daxx knocked out cells prolongs H2O2-induced JNK activation. Moreover, expression of Daxx mutant consisting of its C-terminus dramatically reduces JNK stimulation. Our findings provide an evidence that upon exposure to hydrogen peroxide Daxx prolongs JNK activation dynamics, and the C-terminus of Daxx alone is able to decrease JNK activation and probably participates in the regulation of JNK activation. [ABSTRACT FROM AUTHOR]