SRSF1-mediated translational regulation and its role in cellular transformation

MAGDALENA MASLON; SARA HERAS; NICOLAS BELLORA; JAVIER CACERES

Davos

Congreso; 18th Annual Meeting of the RNA Society; 2013

International RNA Society

SRSF1-mediated translational regulation and its role in cellular transformationMagdalena Maslon1, Sara Heras2, Nicolas Bellora3, Eneritz Aguirre3, Eduardo Eyras3, Javier Caceres11MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, UK;2MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, UKand GENYO-Pfizer, University of Granada, Andalusian Government Centre for Genomics and OncologicalResearch, 18007, Granada, Spain;; 3Regulatory Genomics Group, Universitat Pompeu Fabra, Barcelona, SpainThe serine and arginine-rich protein family (SR proteins) are highly conserved regulators of pre-mRNA splicing. The SRprotein prototype, SRSF1 (also known as SF2/ASF), has been initially characterized as a splicing factor but also shown tomediate post-splicing activities such as mRNA export and translation. SRSF1 has also been proposed to act as an oncogene (1).We have previously shown that SRSF1 promotes translation initiation of bound mRNAs by suppressing the activity of 4E-BP,a competitive inhibitor of cap-dependent translation. This activity is mediated by interactions of SRSF1 with components ofthe mTOR signaling pathway. These findings suggest the model whereby SRSF1 functions as an adaptor protein to recruit thesignaling molecules responsible for regulation of cap-dependent translation of specific mRNAs (2).In order to dissect the importance of SRSF1 in translational control, we have performed a high-throughput deep sequencinganalysis of polysomal fractions in cells overexpressing SRSF1. A group of more than one thousand mRNAs shifts from thesubpolysomal fraction to the heavier polysomal fractions upon SRSF1 overexpression. Interestingly, one third of these mRNAswere previously identified as bona fide RNA targets of this SR protein by CLIP-seq. Bioinformatics analyses showed that thesemRNAs encode proteins involved in cell cycle regulation, such as spindle, kinetochore and M phase proteins, which are essentialfor accurate chromosome segregation. In parallel, protein quantification using SILAC (Stable isotope labelling by amino acids incell culture) confirmed that this subset of proteins was upregulated upon SRSF1 overexpression. Notably, SILAC analysis alsorevealed an increased expression of key glycolytic enzymes upon SRSF1 overexpression and several experiments confirmeda role for SRSF1 in enhancing a glycolytic switch (Warburg effect), a hallmark of proliferating cancer cells. Finally, we haveanalyzed changes in alternative splicing in response to different levels of SRSF1 protein. Interestingly, a significant proportionof those mRNAs that display alternative splicing changes are also translationally regulated by SRSF1. This suggests that SRSF1influences several steps of an mRNA life.Altogether, the finding that SRSF1 promotes the increased translation of genes associated with cell division and also regulatesmetabolic reprogramming in cancer cells could partially explain the oncogenic role of SRSF1. In summary, these data provideinsights on the complex role of SRSF1 in the control of gene expression and its implications in cancer.1. Karni et al. (2007) NatStruct Mol Biol., 14, 185-93.2. Michlewski et al.(2008)Mol Cell, 30, 179-189