Project description:Purpose:Intensive evidence have highlighted the effect of aberrant alternative splicing (AS) events triggered by dysregulation of SR protein family on cancer progression. Nonetheless, the underlying mechanism in breast cancer (BRCA) remains elusive. Here we sought to explore the molecular function of SRSF1 and identify the key AS events regulated by SRSF1 in BRCA. Methods:We conducted comprehensive analysis for the expression and the clinical correlation of SRSF1 in BRCA based on TCGA, Metabric database, clinical tissue samples and BRCA cell lines. Functional analysis of SRSF1 in BRCA was conducted in vitro and in vivo. SRSF1-mediated AS events and its binding motif were identified by RNA-seq, RNA immunoprecipitation-PCR (RIP-PCR) and in vivo crosslinking followed by immunoprecipitation (CLIP), which was further validated by the minigene reporter assay. Finally, the expression and their clinical significance were validated in clinical samples and TCGA database. Results:SRSF1 was upregulated in BRCA samples, associated positively with tumor grade and Ki-67 index, and correlated with poor prognosis in hormone receptor positive (HR+) cohort, which facilitated tumor progression in vitro and in vivo. We identified SRSF1-mediated AS events and discovered the SRSF1 binding motif in the regulation of PTPMT1. Furthermore, PTPMT1 splice switching regulated by SRSF1 partially mediated the oncogenic role of SRSF1 via the AKT/C-MYC axis. Additionally, PTPMT1 splice switching was validated in tissue samples of BRCA patients. Conclusions:Collectively, SRSF1 exerts the oncogenic roles in BRCA partially through regulating AS of PTPMT1, which could be a candidate prognostic factor and therapeutic target in HR+ BRCA cohort.
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