Biomedical subjects

Marion Kubista

Publications and source records attributed to Marion Kubista.

5 recordsLinked to original sources

PubMed2003

Cell size regulation by the human TSC tumor suppressor proteins depends on PI3K and FKBP38.

TSC1 and TSC2 are responsible for the tumor suppressor gene syndrome tuberous sclerosis (TSC). Mammalian TSC genes have been shown to be involved in cell cycle regulation. Recently, in Drosophila, these data have been confirmed and TSC genes have further been demonstrated to affect cell size control. Here we provide supporting data for the fact that the latter function is conserved in mammals. Human TSC1 and TSC2 trigger mammalian cell size reduction and a dominant-negative TSC2 mutant induces increased size. These effects occur in all cell cycle phases, are dependent on the activity of the phosphoinositide-3-kinase and are abolished by co-overexpression of a dominant-negative Akt mutant. Two independent naturally occurring and disease-causing mutations within the TSC2 gene eliminate tuberin's capacity to affect cell size control, emphasizing the relevance of this function for the development of the disease. The same mutations have earlier been shown not to affect tuberin's antiproliferative capacity. That the consequences of modulated TSC gene expression on cell proliferation and on cell size can be assigned to separable functions is further supported by two findings: A mutation within the TSC1 gene, earlier shown to still harbor anti-proliferative effects, was found to eliminate the cell size regulating functions. An important mammalian cell size regulator, c-Myc, was found to inhibit tuberin's antiproliferative capacity, but to have no effects on tuberin-dependent cell size control. To obtain further mechanistical insights, microarray screens for genes involved in TSC1- or TSC2-mediated cell size effects were performed. Antisense experiments revealed that the so observed regulation of the FK506-binding protein, FKBP38, plays a role in TSC gene-dependent cell size regulation. These data provide new insights into mammalian cell size regulation and allow a better understanding of the function of human TSC genes.

Amino Acid Substitution↗

PubMed2002

Brca1 regulates in vitro differentiation of mammary epithelial cells.

Murine Brca1 is widely expressed during development in different tissues. Why alterations of BRCA1 lead specifically to breast and ovarian cancer is currently not clarified. Here we show that Brca1 protein expression is upregulated during mammary epithelial differentiation of HC11 cells, during differentiation of C2C12 myoblasts into myotubes and during neuronal differentiation of N1E-115 cells. Ectopic overexpression of BRCA1 and downregulation of endogenous Brca1 expression specifically affect the regulation of mammary epithelial cell differentiation. Accelerated mammary epithelial cell differentiation upon high ectopic BRCA1 expression is not a consequence of the anti-proliferative capacity of this tumor suppressor and independent of functional p53. Overexpression of the BRCA1 variant lacking the large central exon 11 has no effects on mammary epithelial cell differentiation. These data provide new insights into the cellular role of Brca1.

Animals↗

PubMed2002

Brca1 and differentiation.

Breast cancer is one of the most frequent malignancies affecting women. The human breast cancer gene 1 (BRCA1) gene is mutated in a distinct proportion of hereditary breast and ovarian cancers. Tumourigenesis in individuals with germline BRCA1 mutations requires somatic inactivation of the remaining wild-type allelle. Although, this evidence supports a role for BRCA1 as a tumour suppressor, the mechanisms through which its loss leads to tumourigenesis remain to be determined. Neither the expression pattern nor the described functions of human BRCA1 and murine breast cancer gene 1 (Brca1) can explain the specific association of mutations in this gene with the development of breast and ovarian cancer. Investigation of the role of Brca1 in normal cell differentiation processes might provide the basis to understand the tissue-restricted properties.

Animals↗

PubMed2002

MMP-2 and MMP-9 expression in breast cancer-derived human fibroblasts is differentially regulated by stromal-epithelial interactions.

Tissue remodeling is a key element in the local invasion and metastasis of malignant breast tumors. The degradation of extracellular matrix that is associated with this process is thought to be mediated by a number of Zn2+-dependent matrix metalloproteinases (MMPs). In most cases these enzymes are not produced by the malignant epithelium itself but by adjacent breast stroma, suggesting an important role for cell-cell interactions. We have analyzed Gelatinase A (MMP-2) and Gelatinase B (MMP-9) gene expression in a panel of six breast cancer cell lines and six primary cultures of stromal cells deriving from breast cancer biopsies. With one exception we did not detect MMP-2 or MMP-9 gene expression in any of the established tumor cell lines. Conversely, tumor stroma-derived fibroblasts expressed MMP-2 mRNA. although no MMP-9 mRNA was seen in RNase protection assays. When fibroblasts were cultured in the presence of media conditioned by MCF-7 tumor cells, MMP-2 enzyme production increased but MMP-9 activity remained undetectable. However, when fibroblasts and MCF-7 tumor cells were co-cultured together, MMP-9 was induced. These observations were confirmed by immunocytochemical analysis of co-cultures of MCF-7 and tumor-derived fibroblasts in which MMP-2 and MMP-9 protein expression was confined to stromal cells adjacent to MCF-7 tumor cells. No MMP-2 or MMP-9 staining was detected in monocultures of the two respective cell types. We conclude that MMP-2 expression is present in the stroma of malignant tumors and is increased by paracrine stimulation mediated by soluble factors. In contrast, MMP-9 expression tumor-derived fibroblasts requires direct contact with malignant tumor epithelium.

Breast Neoplasms↗

PubMed2002

Evidence for separable functions of tuberous sclerosis gene products in mammalian cell cycle regulation.

Tuberous sclerosis is an autosomal dominant disease affecting approximately 1 in 6,000 individuals. It is caused by mutations in either TSC1 on chromosome 9q34, which encodes hamartin, or TSC2 on chromosome 16p13.3, which encodes tuberin. The growths, named hamartomas, characteristically occur in different organs of patients and are speculated to result from defects in proliferation control. The observation that hamartin and tuberin can interact in vivo suggests that they might function in the same complex. Here we show that hamartin can affect proliferation control independent of the presence of functional tuberin and that binding to hamartin is not essential for tuberin to affect proliferation. Ectopic expression of hamartin negatively regulates proliferation to a similar extent in tuberin-positive and tuberin-negative cells; this is accompanied by binding to tuberin and upregulation of endogenous p27 in tuberin-positive cells and is without effects on p27 expression in the latter. Our data show for the first time that TSC proteins possess separable functions. We further demonstrate that hamartin can deregulate proliferation control by different mechanisms depending on the presence of tuberin. Besides an overlap in many features of patients with TSC1 and TSC2 mutations, data has accumulated that provides evidence for specific clinical differences. This study provides new insights into the cellular roles of TSC proteins and initiates a discussion of whether separable functions of these proteins might be associated with the clinical differences of TSC1- and TSC2-associated disease.

Animals↗