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Biomedical subjects

Jeffrey D Parvin

Publications and source records attributed to Jeffrey D Parvin.

6 recordsLinked to original sources
PubMed2003

Elongation by RNA polymerase II on chromatin templates requires topoisomerase activity.

Transcription on chromatin by RNA polymerase II (pol II) is repressed as compared with transcription on histone-free DNA. In this study, we show that human topoisomerase I (topo I) and yeast topoisomerase II (topo II), each of which relax both positive and negative superhelical tension, reverse the transcriptional repression by chromatin. In the presence of bacterial topo I, which can relax only negative superhelical tension, the transcription is repressed on chromatin templates. The data together show that the relaxation of positive superhelical tension by these enzymes was the key property required for RNA synthesis from chromatin templates. In the absence of topoisomerase, transcriptional repression on chromatin depended on RNA length. The synthesis of transcripts of 100 nt or shorter was unaffected by chromatin, but repression was apparent when the RNA transcript was 200 nt or longer. These findings suggest that transcription on chromatin templates results in the accumulation of positive superhelical tension by the elongating polymerase, which in turn inhibits further elongation in the absence of topoisomerase activity.

Camptothecin↗
PubMed2003

Overexpression of a protein fragment of RNA helicase A causes inhibition of endogenous BRCA1 function and defects in ploidy and cytokinesis in mammary epithelial cells.

The breast- and ovarian-specific tumor suppressor, BRCA1, has been implicated to function in many nuclear processes, including DNA damage repair, recombination, transcription, ubiquitination, cell cycle checkpoint enforcement, and centrosome regulation. Utilizing a previously described interaction between BRCA1 and RNA helicase A (RHA), we have developed a dominant-negative approach to block BRCA1 function in human breast epithelial cells. Overexpression of a truncated RHA peptide that can bind to the BRCA1 carboxy-terminus prevents normal BRCA1 function, such as BRCA1 association with nuclear foci following DNA damage. Overexpression of this dominant-negative protein induces pleomorphic nuclei, aberrant mitoses with extra centrosomes, and tetraploidy. This model system allows us to observe changes to mammary epithelial cells that occur acutely following loss of BRCA1 function. Furthermore, inhibition of BRCA1 via overexpressing the RHA fragment coincides with a reduction in PARP-1 protein expression, suggesting a possible mechanism for BRCA1 in the maintenance of genomic integrity.

Aneuploidy↗
PubMed2003

The multiple nuclear functions of BRCA1: transcription, ubiquitination and DNA repair.

Interest in BRCA1 stems from its role as a tumour suppressor in breast and ovarian cancer. Intensive research in BRCA1 has revealed little about its specific role in cancer; rather, this protein has been implicated in a multitude of important cellular processes. The diverse biochemical activities of BRCA1 combine to protect the genome from damage. New data reveal that BRCA1 transcriptionally regulates some DNA-repair genes, and, in addition, new roles for BRCA1 have been identified in heterochromatin formation on the X chromosome, double-strand-break repair, and ubiquitination. These diverse activities of BRCA1 may be linked in a single pathway, or BRCA1 might function in multiple nuclear processes.

BRCA1 Protein↗
PubMed2003

Transcription from the perspective of the DNA: twists and bumps in the road.

Although nature's design of the DNA double helix is ingenious for the storage of information, this design creates topological problems for the processes that occur on the DNA. Cellular processes, such as transcription, replication, chromosomal segregation, and chromosomal condensation, are all complicated by the double helix. The problem is compounded in cells since the DNA is in chromatin. Topoisomerases relax positive and negative superhelical turns in DNA, and thereby topoisomerases have long been recognized as key components of the DNA replication and chromosome segregation and condensation machinery. A role for topoisomerases in the transcription process has also been noted in living cells, but only recently has such a role been recapitulated in the test tube for transcription reactions. New data are discussed that demonstrate that for in vitro transcription reactions, topoisomerases are dispensable when the template is naked DNA, but when the template is reconstituted into chromatin, topoisomerases are required for transcription to proceed efficiently.

Animals↗
PubMed2002

The BRCA1 and BARD1 association with the RNA polymerase II holoenzyme.

We have previously shown that endogenous BRCA1 and overexpressed epitope-tagged BRCA1 are present in the transcription complex called the RNA polymerase II holoenzyme (holo-pol). In this study, we further characterized BRCA1 association with the holo-pol by overexpressing deletion mutants of epitope-tagged BRCA1. We found that BRCA1-associated RING domain protein (BARD1) is a component of the holo-pol complex. Deletion of the BRCA1 NH(2) terminus, which is bound by BARD1 as well as other proteins, eliminates >98% of BRCA1 association with the holo-pol. In contrast with earlier observations, deletion of the COOH terminus of BRCA1 did not affect significantly the association with holo-pol. Immunocytochemistry of expressed full-length and deletion mutants of BRCA1 showed that the NH(2) terminus of BRCA1 is important for nuclear dot formation in S-phase. An intact BRCA1 NH(2) terminus is required for the association with holo-pol and for subnuclear localization in S-phase foci. Taken together, these data support a role for BRCA1 regulation of holo-pol function.

Adenoviridae↗