Alternative splicing factor SF2/ASF regulates alternative translation

MATÍAS BLAUSTEIN; LEANDRO QUADRANA; FEDERICO PELISCH; ANABELLA SREBROW

Cold Spring Harbor, USA

Congreso; Cold Spring Harbor Laboratory Meeting on Eukaryotic mRNA Processing; 2007

Serine/Arginine-rich (SR) proteins are important regulators of mRNA splicing. Several post-splicing activities have been described for a subset of shuttling SR proteins, among them SF2/ASF. We show that growth factors (GFs) not only modify alternative splicing of fibronectin EDA exon, but also alter in vivo translation of reporter mRNAs containing the EDA binding motif for SF2/ASF, providing two co-regulated levels of isoform-specific amplification. These effects are inhibited by specific small interfering RNAs (siRNAs) against SF2/ASF and are mediated by the Akt/PKB kinase, which functions as an SR protein kinase. These results show how SR protein activity is modified in response to extracellular stimulation leading to a concerted regulation of splicing and translation. We use bicistronic reporters that generate mRNAs carrying two open reading frames that are respectively translated by cap-dependent or IRES (internal ribosome entry site)-dependent initiation to analyze the possible role of SF2/ASF as a regulator of alternative translation. We show that SF2/ASF over-expression stimulates cap- over IRES-dependent translation, while knocking-down of this splicing factor preferentially stimulates IRES- over cap-dependent translation of these reporters. These effects are currently being studied on alternative translation of an endogenous mRNA.These results propose SF2/ASF as a regulator of alternative translation, expanding its already described potential to increase protein diversity even further.