Portal de Periódicos da CAPES

A splicing mastermind for EMT

2010; Springer Nature; Volume: 29; Issue: 19 Linguagem: Inglês

10.1038/emboj.2010.234

1460-2075

João Paulo Tavanez, Juan Valcárcel,

RNA and protein synthesis mechanisms

Have you seen?6 October 2010free access A splicing mastermind for EMT Joao P Tavanez Joao P Tavanez Centre de Regulació Genòmica, Barcelona, Spain Universitat Pompeu Fabra, Barcelona, Spain Search for more papers by this author Juan Valcárcel Corresponding Author Juan Valcárcel Centre de Regulació Genòmica, Barcelona, Spain Universitat Pompeu Fabra, Barcelona, Spain Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain Search for more papers by this author Joao P Tavanez Joao P Tavanez Centre de Regulació Genòmica, Barcelona, Spain Universitat Pompeu Fabra, Barcelona, Spain Search for more papers by this author Juan Valcárcel Corresponding Author Juan Valcárcel Centre de Regulació Genòmica, Barcelona, Spain Universitat Pompeu Fabra, Barcelona, Spain Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain Search for more papers by this author Author Information Joao P Tavanez1,2 and Juan Valcárcel 1,2,3 1Centre de Regulació Genòmica, Barcelona, Spain 2Universitat Pompeu Fabra, Barcelona, Spain 3Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain *Correspondence to: [email protected] The EMBO Journal (2010)29:3217-3218https://doi.org/10.1038/emboj.2010.234 There is an Article (October 2010) associated with this Have you seen ...?. PDFDownload PDF of article text and main figures. ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InMendeleyWechatReddit Figures & Info Alternative splicing of mRNA precursors is a prevalent mode of gene regulation in multicellular organisms. Important open questions include whether most alternative splicing variants display distinct physiological functions and whether cell type-restricted regulatory factors orchestrate cell type-specific splicing decisions. In this issue of The EMBO Journal, Warzecha et al. (2010) uncover a network of alternative splicing changes contributing to epithelial–mesenchymal transition (EMT), which is controlled by downregulation of the Epithelial Splicing Regulatory Proteins 1 and 2 (ESRP1 and ESRP2). The conversion of epithelial to mesenchymal cells, known as EMT, has important functions in cell differentiation and organogenesis. It also contributes to tissue repair and to disease, with alterations in EMT associated with tissue fibrosis, immunosuppression and carcinogenesis (Thiery et al, 2009). EMT involves striking cellular changes, including loss of cell–cell adhesion and polarity and gain of migratory and even invasive properties. Numerous overlapping signalling pathways (e.g. Wnt and TGF-β) initiate, amplify and modulate EMT, inducing gene expression changes that bring about the cell's phenotypic transitions (Thiery and Sleeman, 2006; Thiery et al, 2009). Thus, activation of transcriptional regulators similar to Snail and transcriptional changes such as down-regulation of E-cadherin or up-regulation of Vimentin are classical landmarks of EMT. The picture emerging from the work of Warzecha et al (2010) in this issue of The EMBO Journal and a previous report from the Carstens' group (Warzecha et al, 2009) is that alternative splicing provides an additional layer of gene regulation that contributes to shape the EMT process. Classical genetic work in Drosophila established the existence of sex-specific splicing regulators, with the female-specific Sex-lethal protein acting as a master regulator (Penalva and Sánchez, 2003). This triggered an interest in the identification of tissue-specific regulatory factors that could explain tissue-specific alternative splicing decisions. In contrast to transcriptional regulation, however, only a handful of tissue-restricted factors were found, leading to the idea that alternative splicing in higher eukaryotes is largely controlled by the relative activity of rather ubiquitous factors (Chen and Manley, 2009). Recent genetic screens in Caenorhabditis elegans and mammalian cells, however, suggest that the list of developmentally and tissue-restricted splicing factors is larger than previously thought (Ohno et al, 2008; Warzecha et al, 2009). Thus, ectopic expression of two related, epithelial cell-specific factors (ESRP1 and ESRP2) was found to induce the expression of epithelial-specific isoforms of fibroblast growth factor receptor 2 as well as of other genes (Warzecha et al, 2009). Could ESRP1 and ESRP2 act as master regulators of epithelial cell-specific splicing, as Sex lethal does for sex-specific splicing in Drosophila? To address this question, Warzecha et al analysed splicing profiles derived from ectopic expression of ESRP1 in mesenchymal cells, as well as from knockdown of ESRP1/ESRP2 in epithelial cells using splicing-sensitive microarrays covering the majority of human alternative splicing events supported by mRNA and EST evidence, and validated microarray predictions by high-throughput RT–PCR analyses. About 100 alternative splicing events showed reciprocal changes in the two experimental situations and are, therefore, candidate targets of ESRP regulation during EMT. These are likely to be direct targets of ESRP proteins because UGG/GUU-rich sequence motifs enriched in the alternatively spliced regions are similar to known ESRP-responsive motifs and can be bound directly by ESRP proteins in vitro. Further sequence and experimental analyses generated a predictive ‘RNA Map’ in which binding of ESRP proteins within or 5′ of an alternative exon leads to exon skipping, whereas binding to the downstream intron leads to exon inclusion (Figure 1), a result remarkably similar to RNA Maps generated for various other regulatory factors (Licatalosi et al, 2008; Yeo et al, 2009; Llorian et al, 2010). Figure 1.ESRP proteins regulate epithelial-specific splicing. The scheme on the left represents splicing patterns influenced by ESRP proteins present specifically in epithelial cells. ESRP binding to GGU/UGG motifs 3′ of regulated exons enhances exon inclusion, whereas ESRP proteins enhance exon skipping when its binding sites are located 5′ of and/or within the regulated exon. The absence of ESRP proteins in mesenchymal cells allows the alternative patterns of splicing to occur, leading to gene expression changes that can contribute to EMT. Download figure Download PowerPoint A second important question is whether ESRP1/2 coordinate a biologically coherent set of alternative splicing decisions contributing to important physiological processes such as EMT? Knockdown of ESRPs results in loss of characteristic morphological features of epithelial cells, concomitant with increased motility and expression of invasive markers, suggestive of acquisition of mesenchymal phenotypes. Some expression changes characteristic of EMT (e.g. up-regulation of Vimentin) were also observed, whereas others (e.g. down-regulation of E-cadherin) were not. Collectively, these observations suggest that ESRP down-regulation contributes to loss of epithelial properties, although EMT requires additional changes in gene expression. Future experiments (e.g. conditional knockout in mice) could delineate the extent to which ESRPs contribute to EMT and its widespread physiological and pathological effects. Although it is not straightforward to predict how the alternative splicing events regulated by ESRPs contribute to physiological changes, ESRP targets include numerous genes representing functional categories relevant to EMT such as cell polarity and motility or cell–cell and cell–matrix adhesion. One interesting example includes components and regulators of the vesicular transport system, which strongly influence cell polarity and adhesion properties. A significant contribution of the work of Warzecha et al is a splicing signature of 10 exons characteristic of epithelial cells, as confirmed in a number of epithelial and mesenchymal cell lines. Such signature can be a valuable marker of EMT, and one of potential clinical use, as cancer cells undergoing EMT are known to display more aggressive tumour phenotypes (Thiery et al, 2009). Evaluation of this splicing signature in a diverse set of carcinomas is, therefore, an important line for future studies, opening also the possibility that ESRPs can themselves be considered therapeutic targets. More generally, these considerations further argue that full understanding of physiological and pathological gene expression programmes requires a detailed analysis of alternative splicing. Conflict of Interest The authors declare that they have no conflict of interest. References Chen M, Manley JL (2009) Mechanisms of alternative splicing regulation: insights from molecular and genomics approaches. Nat Rev Mol Cell Biol 10: 741–754CrossrefCASPubMedWeb of Science®Google Scholar Licatalosi DD, Mele A, Fak JJ, Ule J, Kayikci M, Chi SW, Clark TA, Schweitzer AC, Blume JE, Wang X, Darnell JC, Darnell RB (2008) HITS-CLIP yields genome-wide insights into brain alternative RNA processing. Nature 456: 464–469CrossrefCASPubMedWeb of Science®Google Scholar Llorian M, Schwartz S, Clark TA, Hollander D, Tan LY, Spellman R, Gordon A, Schweitzer AC, de la Grange P, Ast G, Smith CW (2010) Position-dependent alternative splicing activity revealed by global profiling of alternative splicing events regulated by PTB. Nat Struct Mol Biol 17: 1114–1123CrossrefCASPubMedWeb of Science®Google Scholar Ohno G, Hagiwara M, Kuroyanagi H (2008) STAR family RNA-binding protein ASD-2 regulates developmental switching of mutually exclusive alternative splicing in vivo. Genes Dev 22: 360–367CrossrefCASPubMedWeb of Science®Google Scholar Penalva LO, Sánchez L (2003) RNA binding protein sex-lethal (Sxl) and control of Drosophila sex determination and dosage compensation. Microbiol Mol Biol Rev 67: 343–359CrossrefCASPubMedWeb of Science®Google Scholar Thiery JP, Acloque H, Huang RY, Nieto MA (2009) Epithelial-mesenchymal transitions in development and disease. Cell 139: 871–890CrossrefCASPubMedWeb of Science®Google Scholar Thiery JP, Sleeman JP (2006) Complex networks orchestrate epithelial-mesenchymal transitions. Nat Rev Mol Cell Biol 7: 131–142CrossrefCASPubMedWeb of Science®Google Scholar Warzecha CC, Jiang P, Amirikian K, Dittmar KA, Lu H, Shen S, Guo W, Xing Y, Carstens RP (2010) An ESRP-regulated splicing programme is abrogated during the epithelial–mesenchymal transition. EMBO J 29: 3286–3300Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Warzecha CC, Sato TK, Nabet B, Hogenesch JB, Carstens RP (2009) ESRP1 and ESRP2 are epithelial cell-type-specific regulators of FGFR2 splicing. Mol Cell 33: 591–601CrossrefCASPubMedWeb of Science®Google Scholar Yeo GW, Coufal NG, Liang TY, Peng GE, Fu XD, Gage FH (2009) An RNA code for the FOX2 splicing regulator revealed by mapping RNA-protein interactions in stem cells. Nat Struct Mol Biol 16: 130–137CrossrefCASPubMedWeb of Science®Google Scholar Previous ArticleNext Article Read MoreAbout the coverClose modalView large imageVolume 29,Issue 19,October 6, 2010Silver-breasted Broadbill pair ( Serilophus lunatus) - This species of Broadbill are forest-dwellers who build pendulous nests on the forest edge over tracks and roadways. The male and female look similar, except the female has the white necklace, naturally. This image, captured by Graeme Guy of the IMCB in Singapore, scored second place in the “non-scientific” section of the EMBO Journal Cover Contest 2010. View more of Graeme’s wildlife photography at www.grguy.net. If you would like to be reminded when our 2011 contest opens, please send us a brief email at [email protected]. Volume 29Issue 196 October 2010In this issue FiguresReferencesRelatedDetailsLoading ...