Extracellular cues influence fibronectin alternative splicing through an intrincate network of signaling pathways

FEDERICO PELISCH; MATÍAS BLAUSTEIN; LEANDRO QUADRANA; ANABELLA SREBROW

San Francisco, Estados Unidos

Congreso; 45th Annual Meeting of the American Society of Cell Biology; 2005

Alternative pre-mRNA splicing is the most important source of protein diversity in vertebrates. Regulation of this process by extracellular cues represents a key event in the control of gene expression. We use mouse mammary cell lines and the fibronectin gene to study the linkage between the cellular microenvironment and the splicing machinery. We found that a laminin-rich basement membrane down-regulates the inclusion of two fibronectin alternative regions, EDA and IIICS, through a JNK-dependent pathway in epithelial cells. We propose that dephosphorylation of ERK is involved in this regulatory process. By contrast, soluble factors from a mammary mesenchymal cell-conditioned medium as well as different growth factors up-regulate their inclusion via PI 3-kinase. The laminin-rich basement membrane blocks the effect of the mammary mesenchymal cell-conditioned medium, extending the already proposed antagonism between these two signaling pathways to the field of alternative splicing. These results highlight the fact that the splicing pattern of a single transcript is the read out of an intricate network of different signaling cascades. SR proteins have emerged recently as much more than splicing regulators and their activity have been associated to different steps along mRNA metabolism. We found that the signaling pathway triggered by soluble factors not only affect mRNA splicing but also alter translation of reporter mRNAs containing a fibronectin EDA exonic splicing enhancer. These effects on splicing and translation are dependent on SR proteins and can be duplicated by over-expressing a constitutively active AKT, a downstream target of PI 3-kinase. These latter results show how SR protein activity is modified in response to extracellular cues leading to a concerted regulation of splicing and translation.