Project description:Regulation of cell-cell junction formation and regulation of cell migration were enriched among EMT (Epithelial-Mesenchymal Transition)-associated alternatively splicing events. Our analysis suggested that most EMT-associated alternative splicing events are regulated by one or more members of the RBFOX, MBNL, CELF, hnRNP or ESRP classes of splicing factors. The EMT alternative splicing signature was confirmed in human breast cancer cell lines, which could be classified into basal and luminal subtypes based exclusively on their EMTassociated splicing pattern. Expression of EMT-associated alternative mRNA transcripts was also observed in primary breast cancer samples, indicating that EMT-dependent splicing changes occur commonly in human tumors. The functional significance of EMT-associated alternative splicing was tested by expression of the epithelial-specific splicing factor ESRP1 or depletion of RBFOX2 in mesenchymal cells, both of which elicited significant changes in cell morphology and motility towards an epithelial phenotype, suggesting that splicing regulation alone can drive critical aspects of EMT-associated phenotypic changes. The molecular description obtained here may aid in the development of new diagnostic and prognostic markers for analysis of breast cancer progression. Examination of transcriptomes of HMLE/Twist-ER before and after induction of EMT by tamoxifen
Project description:Tumor metastasis remains the major cause of cancer-related death, but its molecular basis is still not well understood. Here we uncovered a splicing-mediated pathway that is essential for breast cancer metastasis. We show that the RNA-binding protein hnRNPM promotes breast cancer metastasis by activating the switch of alternative splicing that occurs during epithelial-mesenchymal transition (EMT). Genome-wide deep sequencing analysis suggests that hnRNPM potentiates TGFb signaling and identifies CD44 as a key downstream target of hnRNPM. hnRNPM ablation prevents TGFb-induced EMT and inhibits breast cancer metastasis in mice, whereas enforced expression of the specific CD44s splice isoform overrides the loss of hnRNPM and permits EMT and metastasis. Mechanistically, we demonstrate that the ubiquitously expressed hnRNPM acts in a mesenchymal-specific manner to precisely control CD44 splice isoform switching during EMT. This restricted cell-type activity of hnRNPM is achieved by competition with ESRP1, an epithelial-splicing regulator that binds to the same cis-regulatory RNA elements and is repressed during EMT. Importantly, hnRNPM is associated with aggressive breast cancer and correlates with increased CD44s in patient specimens. These findings demonstrate a novel molecular mechanism through which tumor metastasis is endowed by the hnRNPM-mediated splicing program. RNAseq for control, hnRNPM siRNA treated lung metastatic LM2 clonal line, derived from the mesenchymal MDA-MB-231 cells
Project description:The epithelial-mesenchymal transition (EMT) is a fundamental developmental process that is abnormally activated in cancer metastasis. Dynamic changes in alternative splicing occur during EMT. ESRP1 and hnRNPM are splicing regulators that promote an epithelial splicing program and a mesenchymal splicing program, respectively. The functional relationships between these splicing factors in the genome-scale remain elusive. Comparing alternative splicing targets of hnRNPM and ESRP1 revealed that they co-regulate a set of cassette exon events, with the majority showing discordant splicing regulation. hnRNPM discordantly regulated splicing events show a positive correlation with splicing during EMT while concordant splicing events do not, highlighting the antagonistic role of hnRNPM and ESRP1 during EMT. Motif enrichment analysis near co-regulated exons identifies guanine-uridine rich motifs downstream of hnRNPM-repressed and ESRP1-enhanced exons, supporting a model of competitive binding to these cis-elements to antagonize alternative splicing. The set of co-regulated exons are enriched in genes associated with cell-migration and cytoskeletal reorganization, which are pathways associated with EMT. Splicing levels of co-regulated exons are associated with breast cancer patient survival and correlate with gene sets involved in EMT and breast cancer subtypes. In conclusion, hnRNPM and ESRP1 co-regulate antagonistically a set of alternative splicing events that occur during EMT. This regulation is likely mediated through competition for the same intronic binding sites downstream of variable exons. hnRNPM and ESRP1 regulated splicing events are associated with breast cancer survival.
Project description:Regulation of cell-cell junction formation and regulation of cell migration were enriched among EMT (Epithelial-Mesenchymal Transition)-associated alternatively splicing events. Our analysis suggested that most EMT-associated alternative splicing events are regulated by one or more members of the RBFOX, MBNL, CELF, hnRNP or ESRP classes of splicing factors. The EMT alternative splicing signature was confirmed in human breast cancer cell lines, which could be classified into basal and luminal subtypes based exclusively on their EMTassociated splicing pattern. Expression of EMT-associated alternative mRNA transcripts was also observed in primary breast cancer samples, indicating that EMT-dependent splicing changes occur commonly in human tumors. The functional significance of EMT-associated alternative splicing was tested by expression of the epithelial-specific splicing factor ESRP1 or depletion of RBFOX2 in mesenchymal cells, both of which elicited significant changes in cell morphology and motility towards an epithelial phenotype, suggesting that splicing regulation alone can drive critical aspects of EMT-associated phenotypic changes. The molecular description obtained here may aid in the development of new diagnostic and prognostic markers for analysis of breast cancer progression.
Project description:Tumor metastasis is the most lethal attribute of breast cancer, and the epithelial-mesenchymal transition (EMT) plays an important role in this process. Alternative splicing has been shown to causally contribute to EMT; however, the scope of critical splicing events and the regulatory network of splicing factors that govern them remain largely unexplored. Here we report the identification of A-Kinase Anchor Protein (AKAP8) as an EMT splicing regulatory factor that impedes EMT and breast cancer metastasis. AKAP8 not only is capable of inhibiting splicing activity of the EMT-promoting splicing regulator hnRNPM through protein-protein interaction, it also binds to RNA directly and alters splicing outcomes. Genome-wide analysis revealed that AKAP8-mediated splicing events, specifically in epithelial cells, are reversely regulated during EMT, suggesting that AKAP8 maintains an epithelial cell-state splicing program. Experimental manipulation of a newly identified AKAP8 splicing target calsyntenin-1 (CLSTN1) revealed that splice isoform switching of CLSTN1 is crucial for EMT. Mining breast cancer patient data supports the experimental findings and AKAP8 expression and the alternative splicing of CLSTN1 predict patient survival. Our work demonstrates the essentiality of RNA metabolism that impinges on metastatic breast cancer.
Project description:Tumor metastasis remains the major cause of cancer-related death, but its molecular basis is still not well understood. Here we uncovered a splicing-mediated pathway that is essential for breast cancer metastasis. We show that the RNA-binding protein hnRNPM promotes breast cancer metastasis by activating the switch of alternative splicing that occurs during epithelial-mesenchymal transition (EMT). Genome-wide deep sequencing analysis suggests that hnRNPM potentiates TGFb signaling and identifies CD44 as a key downstream target of hnRNPM. hnRNPM ablation prevents TGFb-induced EMT and inhibits breast cancer metastasis in mice, whereas enforced expression of the specific CD44s splice isoform overrides the loss of hnRNPM and permits EMT and metastasis. Mechanistically, we demonstrate that the ubiquitously expressed hnRNPM acts in a mesenchymal-specific manner to precisely control CD44 splice isoform switching during EMT. This restricted cell-type activity of hnRNPM is achieved by competition with ESRP1, an epithelial-splicing regulator that binds to the same cis-regulatory RNA elements and is repressed during EMT. Importantly, hnRNPM is associated with aggressive breast cancer and correlates with increased CD44s in patient specimens. These findings demonstrate a novel molecular mechanism through which tumor metastasis is endowed by the hnRNPM-mediated splicing program.
Project description:Alternative splicing achieves coordinated changes in post-transcriptional gene expression programs through the activities of diverse RNA binding proteins. Epithelial Splicing Regulatory Proteins 1 and 2 (ESRP1 and ESRP2) are cell type-specific regulators of transcripts that switch splicing during the Epithelial Mesenchymal Transition (EMT). To define a comprehensive program of alternative splicing that is regulated during the EMT, we identified an extensive ESRP-regulated splicing network of hundreds of alternative splicing events within numerous genes with roles in cell-cell adhesion, polarity, and migration. Loss of this global ESRP-regulated epithelial splicing program induces the phenotypic changes in cell morphology that are observed during the EMT. Components of this splicing signature provide novel molecular markers that can be used to characterize the EMT. Bioinformatics and experimental approaches revealed a high affinity ESRP binding motif and a predictive RNA map that governs their activity. This work establishes the ESRPs as coordinators of a complex alternative splicing network that adds an important post-transcriptional layer to the changes in gene expression that underlie epithelial-mesenchymal transitions during development and disease. Keywords: control / knockdown comparison and control / ectopic expression comparison
Project description:The epithelial-to-mesenchymal transition (EMT) contributes to tumor heterogeneity and has been implicated in tumor initiation and metastasis. To systematically identify genes involved in EMT, we performed a genome-scale expression screen in human mammary epithelial cells and found a striking enrichment in RNA splicing factors. In particular, the RNA-binding proteins QKI and RBFOX1 were necessary and sufficient to promote EMT and stem-like states. Among the transcripts cooperatively regulated by both factors, we found that alternative splicing of the actin-binding protein FLNB plays an essential role in the regulation of EMT. The skipping of FLNB exon 30 and the elevated expression of QKI were strongly associated with EMT gene signatures in both basal B subtype breast cancer cell lines and basal-like breast cancer patient samples. These observations demonstrate that alternative splicing regulated by QKI and RBFOX1 plays an active role in promoting EMT in basal-like breast cancers.
Project description:The epithelial-to-mesenchymal transition (EMT) contributes to tumor heterogeneity and has been implicated in tumor initiation and metastasis. To systematically identify genes involved in EMT, we performed a genome-scale expression screen in human mammary epithelial cells and found a striking enrichment in RNA splicing factors. In particular, the RNA-binding proteins QKI and RBFOX1 were necessary and sufficient to promote EMT and stem-like states. Among the transcripts cooperatively regulated by both factors, we found that alternative splicing of the actin-binding protein FLNB plays an essential role in the regulation of EMT. The skipping of FLNB exon 30 and the elevated expression of QKI were strongly associated with EMT gene signatures in both basal B subtype breast cancer cell lines and basal-like breast cancer patient samples. These observations demonstrate that alternative splicing regulated by QKI and RBFOX1 plays an active role in promoting EMT in basal-like breast cancers.
Project description:Malignant progression in cancer has been associated with the emergence of populations of tumor-initiating cells (TIC) endowed with capabilities for unlimited self-renewal, survival under stress and establishment of distant metastases. Additionally, the acquisition of invasive properties driven by the genetic program known as epithelialmesenchymal transition (EMT) may be an essential step in the evolution of neoplastic cells into fully metastatic populations. A widely accepted paradigm is that EMT potentiates tumor cell self-renewal and metastatic behaviour. Here we describe a cellular model in which a clonal population enriched in TIC expresses a genetic program distinct from a second population with traits of stable EMT, and in which both populations cooperate for enhanced local invasiveness and metastasis. Induction of the TIC-enriched population to undergo EMT by several stimuli or by constitutive overexpression of the transcription factor SNAI1 engaged a mesenchymal program while suppressing the CSC program. This suggests that TIC and EMT, contrary to current paradigms, correspond to alternative states. Furthermore, diffusible factors secreted by the population with EMT traits also induced mesenchymal reprogramming of the population enriched in CSCs. Local invasiveness in vitro and lung colonization in vivo of the TIC-enriched population was enhanced by co-injection with the EMT-trait population, and expanded the range of organs to which it metastasized. Thus, in our model, relatively stable TIC and EMT phenotypes reflect alternative genetic programs expressed by distinct clonal populations. We also suggest that dynamic cooperation between tumor subpopulations displaying either TIC or EMT traits may be a general mechanism driving local invasiveness and metastasis. The complete database comprised the expression measurements of 54 675 genes for PC-3/Mc (n=3) and PC-3/S (n=3)