Epithelial-mesenchymal interaction and its influence on fibronectin alternative splicing

MATÍAS BLAUSTEIN; ALBERTO R. KORNBLIHTT; ANABELLA SREBROW

Villa Carlos Paz, Argentina

Congreso; Reunión Anual de la Sociedad Argentina de Investigaciones Bioquímicas - SAIB; 2001

Alternative splicing generates distinct proteins from a single gene. In the case of the fibronectin gene, one primary transcript gives rise to different mRNAs by alternative splicing occurring in three regions (EDII, EDI and IIICS). EDI+ fibronectin is poorly represented in the extracellular matrix of adult normal tissues but is overexpressed in developing embryos and pathological conditions. Alternative splicing regulation by extracellular signals is crucial for altering gene expression during development and cell differentiation and according to the physiological state of cells. Communication between epithelial and stromal compartments is critical for epithelial morphogenesis. This is particularly evident during mammary gland development. We proposed to study the effect of epithelial-mesenchymal interaction on the alternative splicing of fibronectin pre-mRNA. We observed that a mammary mesenchymal cell line expressed higher levels of EDI+ fibronectin than a mammary epithelial cell line. We asked whether the interaction between these two cell lines, that induces epithelial differentiation, could modify the pattern of fibronectin alternative splicing. By co-culture experiments, we showed that soluble factors secreted by mesenchymal cells stimulate the inclusion of the EDI exon in epithelial cells, increasing by 4 fold the EDI+/EDI- ratio. When epithelial cells were treated with conditioned medium from mesenchymal cells, not only the EDI+/EDI- ratio was increased but also the cells partially loose their phenotype. Our goal is to elucidate the molecules and the signal transduction pathways involved in the regulation of fibronectin alternative splicing in epithelial cells triggered by mesenchymal cells.