Epithelial-mesenchymal interaction, fibronectin and alternative splicing

MATÍAS BLAUSTEIN; FEDERICO PELISCH; OMAR A. COSO; ALBERTO R. KORNBLIHTT; ANABELLA SREBROW

Iguazú, Argentina

Simposio; ICGEB symposium: “Gene Expression and RNA Processing"; 2003

Alternative splicing generates distinct proteins from a single gene, and about fifty percent of the human genes undergo this process. Fibronectin, which is the most widely and best characterized extracellular matrix glycoprotein, plays a key role in cell adhesive and migratory behaviour and provides a complex and paradigmatic model of alternative splicing. Dynamic communication between mammary epithelium and stroma and their interaction with the extracellular matrix is required for proper patterning and function of the normal mammary gland. In this physiological context, we study the effect of extracellular signals on the regulation of fibronectin pre-mRNA alternative splicing. We have found that soluble factors present in a mammary mesenchymal cell-conditioned medium, as well as different growth factors, stimulate the inclusion of the alternatively spliced fibronectin EDI exon in mammary epithelial cells, inducing cell scattering concomitantly. This regulatory phenomenon is independent from promoter structure and is not observed when EDI exon lacks two exonic elements (splicing enhancer and splicing silencer). By using different approaches we conclude that the PI3K pathway is the main responsible for the regulation of EDI splicing in this cellular context. On the other hand, inhibition of the JNK pathway potentiates the effects of different stimuli on the inclusion of this exon. Finally, we show that splicing regulation of IIICS, another fibronectin alternative exon, correlates well with the described regulation for EDI. However, the inclusion of the third fibronectin alternative exon, EDII, is not influenced at all by any of these stimuli. Taken together, these results strengthen our understanding of how extracellular stimuli are converted into changes in splicing patterns.