Cell cycle-dependent regulation of the bi-directional overlapping promoter of human BRCA2/ZAR2 genes in breast cancer cells

<p>Abstract</p> <p>Background</p> <p>BRCA2 gene expression is tightly regulated during the cell cycle in human breast cells. The expression of BRCA2 gene is silenced at the G0/G1 phase of cell growth and is de-silenced at the S/G2 phase. While studying the activity of BRCA2 gene promoter in breast cancer cells, we discovered that this promoter has bi-directional activity and the product of the reverse activity (a ZAR1-like protein, we named ZAR2) silences the forward promoter at the G0/G1 phase of the cell. Standard techniques like cell synchronization by serum starvation, flow cytometry, N-terminal or C-terminal FLAG epitope-tagged protein expression, immunofluorescence confocal microscopy, dual luciferase assay for promoter evaluation, and chromatin immunoprecipitation assay were employed during this study.</p> <p>Results</p> <p>Human <it>BRCA2 </it>gene promoter is active in both the forward and the reverse orientations. This promoter is 8-20 fold more active in the reverse orientation than in the forward orientation when the cells are in the non-dividing stage (G0/G1). When the cells are in the dividing state (S/G₂), the forward activity of the promoter is 5-8 folds higher than the reverse activity. The reverse activity transcribes the ZAR2 mRNA with 966 nt coding sequence which codes for a 321 amino acid protein. ZAR2 has two C4 type zinc fingers at the carboxyl terminus. In the G0/G1 growth phase ZAR2 is predominantly located inside the nucleus of the breast cells, binds to the BRCA2 promoter and inhibits the expression of BRCA2. In the dividing cells, ZAR2 is trapped in the cytoplasm.</p> <p>Conclusions</p> <p><it>BRCA2 </it>gene promoter has bi-directional activity, expressing BRCA2 and a novel C4-type zinc finger containing transcription factor ZAR2. Subcellular location of ZAR2 and its expression from the reverse promoter of the BRCA2 gene are stringently regulated in a cell cycle dependent manner. ZAR2 binds to BRCA2/ZAR2 bi-directional promoter <it>in vivo </it>and is responsible, at least in part, for the silencing of BRCA2 gene expression in the G0/G1 phase in human breast cells.</p

Melorheostosis: Two atypical cases

Melorheostosis is an uncommon mesenchymal dysplasia that rarely affects the axial skeleton.We describe two atypical cases of melorheostosis with classical imaging findings - the first one involving the cervico-dorsal spine with encroachment of left vertebral artery canal causing attenuation of the left vertebral artery and the second one of mixed sclerosing bony dysplasia (monomelic involvement coexisting with osteopoikilosis)

Neural fibrolipoma in pharyngeal mucosal space: A rare occurrence

Neural fibrolipoma is a rare lesion presenting in early childhood, as a slow-growing fusiform swelling of a nerve, usually in the forearm or wrist (median nerve), associated with symptoms of compression neuropathy. There are only few case reports of neural fibrolipoma in neck and no such case has been reported in pharyngeal mucosal space

Characterization of natural antimony resistance in Leishmania Donovani isolates

Clinical resistance to pentavalent antimonial compounds has long been recognized as a major problem in the treatment of visceral leishmaniasis in India. However, mechanisms of natural resistance are unclear. In this study, we observed that Leishmania donovani clinical isolates not responsive to sodium stibogluconate showed resistance to antimony treatment in both in vitro and in vivo laboratory conditions. The resistant isolates have increased levels of intracellular thiols. This increase in thiol levels was not mediated by the amplification of ?-glutamylcysteine synthetase, but was accompanied by amplification of trypanothione reductase and an intracellular ATP-binding cassette transporter gene MRPA. The resistance of parasites to antimony could be reversed by the glutathione biosynthesis-specific inhibitor, buthionine sulfoximine, which resulted in increased drug susceptibility. These results suggest the possible role of thiols and MRPA in antimony resistance in field isolates