Biomedical subjects

Vishwanie Budhram-Mahadeo

Publications and source records attributed to Vishwanie Budhram-Mahadeo.

5 recordsLinked to original sources

PubMed2006

The Brn-3b POU family transcription factor represses plakoglobin gene expression in human breast cancer cells.

The Brn-3b transcription factor has been shown to be overexpressed in human breast cancer cells and contributes toward cell growth regulation. Using micro-arrays, more than 50 cancer-related genes regulated by Brn-3b in human breast cancer cells have been identified. For example, Brn-3b activates the cell cycle regulator CDK4 that provides a mechanism by which Brn-3b controls the growth of breast cancer cells. Here, we show that Brn-3b regulates plakoglobin (gamma-catenin), a member of the catenin family involved in cell-cell adhesion and signal transduction. Brn-3b expression inversely correlates with plakoglobin expression at both mRNA and protein levels in breast cancer cell lines and human breast biopsies. In contrast, no significant correlation was observed between Brn-3b expression and beta-catenin, or between Brn-3b expression and E-cadherin expression. Brn-3b represses the plakoglobin promoter via a Brn-3 consensus binding site contained within the region -965 to -593 relative to the transcriptional start site. Both repression of the promoter and binding of Brn-3b are lost when this site is mutated. To our knowledge, this is the first time that a Brn-3b POU family transcription factor has been shown to regulate a member of the catenin family, which provides insight into the molecular mechanisms by which Brn-3b expression may favour breast cancer progression and tumor invasion.

Binding Sites↗

PubMed2004

Activation of CDK4 gene expression in human breast cancer cells by the Brn-3b POU family transcription factor.

The Brn-3b POU family transcription factor has previously been shown to be over-expressed in human breast cancer and to enhance the growth rate and anchorage independent growth of human breast cancer cells, acting at least in part by inhibiting the expression of the BRCA-1 anti-oncogene. Here we have used gene arrays to identify several other targets for Brn-3b in human breast cancer cells, including cyclin-dependent kinase 4 (CDK4). In particular, we show that levels of CDK4 mRNA and protein correlate with the levels of Brn-3b in breast cancer cell lines manipulated to express different levels of Brn-3b and in human breast cancer biopsies and that Brn-3b can activate the CDK4 promoter. The effect of Brn-3b on the growth regulatory CDK4 protein provides a further mechanism by which Brn-3b can regulate breast cancer cell growth and indicates that it can do this by activating as well as repressing specific target genes.

Biopsy↗

PubMed2004

The Brn-3b transcription factor regulates the growth, behavior, and invasiveness of human neuroblastoma cells in vitro and in vivo.

Neuroblastomas are the second most common solid tumor in children but the molecular mechanisms underlying the initiation and progression of this disease are poorly understood. We previously showed that the Brn-3b transcription factor is highly expressed in actively proliferating neuroblastoma cells but is significantly decreased when these cells are induced to differentiate. In this study, we analyzed the effects of manipulating Brn-3b levels in the human neuroblastoma cell line, IMR-32 and showed that constitutive overexpression of Brn-3b consistently increased cellular growth and proliferation in monolayer as well as in an anchorage-independent manner compared with controls whereas stably decreasing Brn-3b can reduce the rate of growth of these cells. Cells with high Brn-3b also fail to respond to growth inhibitory retinoic acid, as they continue to proliferate. Moreover, Brn-3b levels significantly modified tumor growth in vivo with elevated Brn-3b resulting in faster tumor growth in xenograft models whereas decreasing Brn-3b resulted in slower growth compared with controls. Interestingly, elevated Brn-3b levels also enhances the invasive capacity of these neuroblastoma cells with significantly larger numbers of migrating cells observed in overexpressing clones compared with controls. Because invasion and metastasis influence morbidity and mortality in neuroblastoma and so significantly affect the course and outcome of neuroblastomas, this finding is very important. Our results therefore suggest that Brn-3b transcription factor contributes to proliferation of neuroblastoma cells in vivo and in vitro but may also influence progression and/or invasion during tumorigenesis. It is possible that decreasing Brn-3b levels may reverse some effects on growth and proliferation of these cells.

Cell Adhesion↗

PubMed2002

The Brn-3a POU family transcription factor stimulates p53 gene expression in human and mouse tumour cells.

The Brn-3a POU family transcription factor is able to induce the expression of genes encoding anti-apoptotic proteins such as Bcl-2 and Bcl-x and protects neuronal cells from apoptosis. This effect is opposed by the pro-apoptotic p53 protein which completely inhibits the ability of Brn-3a to activate the Bcl-2 and Bcl-x promoters. Here we demonstrate that Brn-3a is able to stimulate p53 expression. Thus, in co-transfection experiments, Brn-3a activates the p53 promoter acting via a region from +22 to +67, located between the most proximal (+1) and the most distal (+105) transcriptional start sites. Similarly, reduction of Brn-3a expression using anti-sense constructs reduces endogenous p53 expression in human neuroblastoma or cervical carcinoma cell lines growing in vitro and as tumours in nude mice whilst increasing Brn-3a levels enhances p53 expression. These results suggest the existence of a negative feedback loop in which elevated Brn-3a expression induces the expression of p53 which, in turn, antagonises the anti-apoptotic activity of Brn-3a.

Animals↗

PubMed2002

Functional interaction between Brn-3a and Src-1 co-activates Brn-3a-mediated transactivation.

The Brn-3a POU domain transcription factor is able to regulate the transcription of promoters containing a Brn-3 response element via its POU domain. In addition, the POU domain of Brn-3a has been shown to functionally interact with the estrogen receptor and regulate transcription from estrogen responsive promoters. The steroid receptor coactivator, Src-1, enhances transcription with a variety of steroid receptors. Here we describe a functional interaction between Brn-3a and Src-1. In glutathione S-transferase pull-down assays Src-1 was shown to specifically interact with Brn-3 proteins. Moreover, Src-1 co-immunoprecipitated from intact cells with Brn-3a. The transactivation potential of the Brn-3a/Src-1 complex was tested on both the Brn-3 responsive SNAP-25 promoter and the estrogen responsive vitellogenin promoter, in each of two different cell lines, the neuronal ND7 cell line, and the kidney BHK21 cell line. Src-1 consistently and strongly potentiated the activation of Brn-3a on the SNAP promoter construct in both the ND7 and BHK21 cell lines. The vitellogenin promoter construct, however, was only weakly activated by the Brn-3/Src-1 complex in the ND7 cells and there was even less effect on this promoter in the BHK21 cells. These results suggest a functional role for Src-1 in enhancing Brn-3a mediated transactivation, seemingly independent of nuclear hormone receptors, thus broadening the transcriptional repertoire of both Brn-3a and Src-1.

Animals↗