Biomedical subjects

Alt Zantema

Publications and source records attributed to Alt Zantema.

5 recordsLinked to original sources

PubMed2003

Loss of CBP acetyltransferase activity by PHD finger mutations in Rubinstein-Taybi syndrome.

Disruption of one copy of the human CREB binding protein (CBP or CREBBP) gene leads to the Rubinstein-Taybi syndrome (RTS), a developmental disorder characterized by retarded growth and mental functions, broad thumbs, broad big toes and typical facial abnormalities. The CREB binding protein (CBP) is an essential transcriptional coactivator for many different transcription factors. CBP has the intrinsic ability to acetylate histones and other proteins, which is regarded as an important step in transcription activation. In vitro studies have shown that this enzymatic activity critically depends on the integrity of a plant homeodomain (PHD)-type zinc finger in the HAT domain of CBP. We therefore investigated whether PHD finger mutations are present in RTS patients. Mutational analysis of 39 patients revealed eight novel heterozygous mutations in the HAT domain of CBP, one of which alters a conserved PHD finger amino acid (E1278K), while a second mutation deletes exon 22, which encodes the central region of the PHD finger. Functional analysis of these RTS-associated PHD finger mutants showed that they lacked in vitro acetyltransferase activity towards histones and CBP itself and displayed reduced coactivator function for the transcription factor CREB. Importantly, in EBV-transformed lymphoblastoid cells from the exon 22 deletion patient we found approximately 50% less endogenous CBP HAT activity. These findings therefore underscore the functional importance of the PHD finger in vivo and imply that reduction of CBP HAT activity, as exemplified here by disruption of the PHD finger, is sufficient to cause RTS.

Acetyltransferases↗

PubMed2003

Cascade of distinct histone modifications during collagenase gene activation.

Gene activation in eukaryotes requires chromatin remodeling, in part via histone modifications. To study the events at the promoter of a mitogen-inducible gene, we examined the induction of expression of the collagenase gene. It has been established that the collagenase gene can be activated by c-Jun and c-Fos and that the transcriptional coactivator p300 is involved in the activation. As expected, we found histone acetyltransferase activity at the collagenase promoter during activation. Interestingly, we also found histone methyltransferase and kinase activity. Strikingly, the first modification observed is methylation of histone H3 lysine 4, which correlates with the binding of the SET9 methyltransferase and the assembly of a complex consisting of c-Jun, c-Fos, TATA binding protein, and RNA polymerase II. The assembly of the preinitiation complex also shows an ordered binding of the acetyltransferase p300, the RSK2 kinase, and the SWI/SNF component Brg-1. Our results suggest that collagenase gene activation involves a dynamic recruitment of different factors and that in addition to acetylation, histone H3 lysine 4 di- and trimethylation and histone H3 serine 10 phosphorylation are important steps in the activation of this gene.

Acetyltransferases↗

PubMed2002

Differential expression of tapasin and immunoproteasome subunits in adenovirus type 5- versus type 12-transformed cells.

Adenovirus type 12 (Ad12)-transformed baby rat kidney (BRK) cells are oncogenic in syngeneic immunocompetent rats in contrast to adenovirus type 5 (Ad5)-transformed BRK cells, which are not oncogenic in these animals. A significant factor contributing to the difference in oncogenicity may be the low levels of major histocompatibility complex (MHC) class I membrane expression in Ad12-transformed BRK cells as compared with those in Ad5-transformed BRK cells, which presumably results in escape from killing by cytotoxic T lymphocytes. Here we show that, in addition to the decreased levels of expression of the MHC class I heavy chain and the peptide transporter Tap-2, the expression levels of the chaperone Tapasin and the immunoproteasome components MECL-1, PA28-alpha, and PA28-beta also are much lower in Ad12- than in Ad5-transformed BRK cells. The low expression levels of these proteins may contribute to the escape from killing by cytotoxic T lymphocytes, because the generation of optimal peptides and loading of these peptides on MHC class I require these components. Increased levels of phosphorylated signal transducer and activator of transcription-1 protein and expression of IFN regulatory factor-7 were found in Ad5- versus Ad12-transformed BRK cells. Therefore, the critical alteration leading to the plethora of differences may be an interferon (-related) effect.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2002

The PHD type zinc finger is an integral part of the CBP acetyltransferase domain.

Histone acetyltransferases (HATs) such as CBP and p300 are regarded as key regulators of RNA polymerase II-mediated transcription, but the critical structural features of their HAT modules remain ill defined. The HAT domains of CBP and p300 are characterized by the presence of a highly conserved putative plant homeodomain (PHD) (C4HC3) type zinc finger, which is part of the functionally uncharacterized cysteine-histidine-rich region 2 (CH2). Here we show that this region conforms to the PHD type zinc finger consensus and that it is essential for in vitro acetylation of core histones and the basal transcription factor TFIIE34 as well as for CBP autoacetylation. PHD finger mutations also reduced the transcriptional activity of the full-length CBP protein when tested on transfected reporter genes. Importantly, similar results were obtained on integrated reporters, which reflect a more natural chromatinized state. Taken together, our results indicate that the PHD finger forms an integral part of the enzymatic core of the HAT domain of CBP.

Acetylation↗

PubMed2002

Scaffold/matrix attachment region elements interact with a p300-scaffold attachment factor A complex and are bound by acetylated nucleosomes.

The transcriptional coactivator p300 regulates transcription by binding to proteins involved in transcription and by acetylating histones and other proteins. These transcriptional effects are mainly at promoter and enhancer elements. Regulation of transcription also occurs through scaffold/matrix attachment regions (S/MARs), the chromatin regions that bind the nuclear matrix. Here we show that p300 binds to the S/MAR binding protein scaffold attachment factor A (SAF-A), a major constituent of the nuclear matrix. Using chromatin immunoprecipitations, we established that both p300 and SAF-A bind to S/MAR elements in the transiently silent topoisomerase I gene prior to its activation at G(1) during cell cycle. This binding is accompanied by local acetylation of nucleosomes, suggesting that p300-SAF-A interactions at S/MAR elements of nontranscribed genes might poise these genes for transcription.

Acetylation↗