Biomedical subjects

Evangelos Kiskinis

Publications and source records attributed to Evangelos Kiskinis.

5 recordsLinked to original sources

PubMed2006

The SWI/SNF chromatin remodeling subunit BAF57 is a critical regulator of estrogen receptor function in breast cancer cells.

Estrogen receptors (ERs) play critical roles in both normal mammary gland development and in the formation and progression of breast tumors, constituting a major therapeutic target for breast cancer treatment. We have previously described that ER transcriptional activity is potentiated by BAF57, a core subunit of the mammalian SWI/SNF chromatin remodeling complex. Here we provide evidence demonstrating an important role for BAF57 as regulator of ER functions in breast cancer cells. Different experimental manipulations leading to the abrogation of BAF57 expression and/or function severely reduced the expression of various endogenous ER target genes and blocked estrogen-stimulated proliferation in ZR-75-1 breast cancer cells. Moreover, using a structure-function analysis, we have defined the protein domains required for the functional interaction between ERalpha and BAF57, including a key region within the hinge of ERalpha that is essential for BAF57 recruitment and its function on ER-mediated transcription. Interestingly, we found that BAF57 is an ER subtype-selective modulator that specifically regulates ERalpha-mediated transcription. Taken together, our results suggest that targeting BAF57 could represent a new way to effectively inhibit the action of ERalpha.

Breast Neoplasms↗

PubMed2006

Identification of BAF57 mutations in human breast cancer cell lines.

Accumulating genetic and biochemical evidences support a role for the SWI/SNF chromatin-remodeling complex in cancer development and multiple core subunits of these complexes have been found to function as tumor suppressor genes. The core SWI/SNF subunit BAF57 mediates direct interactions with estrogen and androgen receptors (ER and AR) regulating their transcriptional activity. BAF57 gene maps to chromosome band 17 q21 in close proximity to the BRCA1 gene. This locus has been associated with frequent loss of heterozygosity (LOH) and allelic imbalance in breast cancers; however, BRCA1 mutations are rare events in sporadic breast cancer with LOH in the region, suggesting that another tumor suppressor gene resides in this area. All these reasons prompted us to screen for mutations in the BAF57 gene using a panel of the most commonly used human breast cancer cell lines. All cell lines analysed contain wild-type copies of BAF57 gene with the only exception of the breast ductal carcinoma cell line BT549. Sequencing of genomic DNA and cDNA generated from BT549 mRNA demonstrated the presence of a CA dinucleotide insertion in exon 5 of BAF57. The absence of wild-type BAF57 alleles indicates that this is a biallelic inactivating mutation that causes a frameshift and as a consequence a premature stop codon leading to a truncated BAF57 protein. A functional characterisation of the truncated BAF57 showed that it has lost the ability to bind to ER but still binds to the nuclear receptor coactivator SRC1e. Furthermore, we observed that the expression of the truncated BAF57 increased the ability of SRC1e to potentiate transcriptional activation by ERalpha, suggesting that mutations in BAF57 could contribute to the oncogenic transformation in breast cancer cells.

Amino Acid Sequence↗

PubMed2005

Suppression of oxidative metabolism and mitochondrial biogenesis by the transcriptional corepressor RIP140 in mouse adipocytes.

Using an siRNA-based screen, we identified the transcriptional corepressor RIP140 as a negative regulator of insulin-responsive hexose uptake and oxidative metabolism in 3T3-L1 adipocytes. Affymetrix GeneChip profiling revealed that RIP140 depletion upregulates the expression of clusters of genes in the pathways of glucose uptake, glycolysis, TCA cycle, fatty acid oxidation, mitochondrial biogenesis, and oxidative phosphorylation in these cells. Conversely, we show that reexpression of RIP140 in mouse embryonic fibroblasts derived from RIP140-null mice downregulates expression of many of these same genes. Consistent with these microarray data, RIP140 gene silencing in cultured adipocytes increased both conversion of [14C]glucose to CO2 and mitochondrial oxygen consumption. RIP140-null mice, previously reported to resist weight gain on a high-fat diet, are shown here to display enhanced glucose tolerance and enhanced responsiveness to insulin compared with matched wild-type mice upon high-fat feeding. Mechanistically, RIP140 was found to require the nuclear receptor ERRalpha to regulate hexose uptake and mitochondrial proteins SDHB and CoxVb, although it likely acts through other nuclear receptors as well. We conclude that RIP140 is a major suppressor of adipocyte oxidative metabolism and mitochondrial biogenesis, as well as a negative regulator of whole-body glucose tolerance and energy expenditure in mice.

3T3 Cells↗

PubMed2005

RIP140-targeted repression of gene expression in adipocytes.

Ligand-dependent repression of nuclear receptor activity forms a novel mechanism for regulating gene expression. To investigate the intrinsic role of the corepressor RIP140, we have monitored gene expression profiles in cells that express or lack the RIP140 gene and that can be induced to undergo adipogenesis in vitro. In contrast to normal white adipose tissue and in vitro-differentiated wild-type adipocytes, RIP140-null cells show elevated energy expenditure and express high levels of the uncoupling protein 1 gene (Ucp1), carnitine palmitoyltransferase 1b, and the cell-death-inducing DFF45-like effector A. Conversely, all these changes are abrogated by the reexpression of RIP140. Analysis of the Ucp1 promoter showed RIP140 recruitment to a key enhancer element, demonstrating a direct role in repressing gene expression. Therefore, reduction in the levels of RIP140 or prevention of its recruitment to nuclear receptors may provide novel mechanisms for the control of energy expenditure in adipose cells.

Adaptor Proteins, Signal Transducing↗

PubMed2002

High throughput Comet assay using 96-well plates.

The single-cell gel electrophoresis or Comet assay is becoming established as an industrial genotoxicity screening test. The aim of this study was to increase the throughput of compounds tested and to minimize the amount of test compound needed for an assay. We modified practical aspects of our standard protocol and designed an experimental procedure suitable for use with 96-well plates. By using a suspension culture rather than attached cells, the modified protocol enabled parallel testing of four compounds on a single microplate (10 duplicate concentrations per compound). A significant reduction in work time was achieved by replacing the previously used Trypan blue dye exclusion (TBDE) test by an automated measurement of ATP levels as the concurrent viability test. The rapid and easy to perform ATP test was carried out towards the end of the 3 h treatment. In this way we were able to select for further analysis and slide preparation only those concentrations which induced the desired range of cytotoxicity. The suitability of the modified test conditions and reproducibility of test results was demonstrated by results obtained with standard mutagens and eight drug candidates tested at various concentrations. In each case the results obtained with the standard and the modified protocols were comparable. By introducing the changes to our standard protocol, combined with automated image analysis, we were able to more than double our previous throughput.

Adenosine Triphosphate↗