Concerted regulation of alternative splicing and translation by extracellular cues through SR proteins

MATÍAS BLAUSTEIN; FEDERICO PELISCH; TAMARA TANOS; MANUEL J. MUÑOZ; ANABELLA SREBROW

Cold Spring Harbor, Estados Unidos

Congreso; Cold Spring Harbor Laboratory meeting on Eukaryotic mRNA Processing; 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 the fibronectin gene as a model to study the linkage between the extracellular microenvironment and the splicing machinery. We found that cell-ECM interaction down-regulates the inclusion of the fibronectin alternative exon EDA through a JNK-dependent pathway. By contrast, cell-cell interaction and growth factors up-regulate the inclusion of this exon via PI3K in an SR-protein dependent fashion. We show a negative cross-talk between these two signaling pathways, highlighting the fact that the splicing pattern of a single transcript is the read out of an intricate network of different signaling cascades. We extended our studies to other SR protein-mediated activities involved in mRNA metabolism and found that cell-cell interaction and growth factors also alter translation of reporter mRNAs containing a fibronectin EDA exonic splicing enhancer. The effects at both splicing and translation levels are inhibited by specific small interfering RNAs against the SR proteins 9G8 and SF2, and are mediated by the AKT kinase. Furthermore, we demonstrate that AKT phosphorylates these two SR proteins in vitro and elicits opposite effects to those evoked by SR protein kinases Clk/Sty and SRPK on SR protein localization and alternative splicing in cultured cells. These latter results show how SR protein activity is modified in response to extracellular cues leading to a concerted regulation of splicing and translation.