title: Direct Regulation of Alternative Splicing by SMAD3 through PCBP1 Is Essential to the Tumor-Promoting Role of TGF-β.
abstract: In advanced stages of cancers, TGF-β promotes tumor progression in conjunction with inputs from receptor tyrosine kinase pathways. However, mechanisms that underpin the signaling cooperation and convert TGF-β from a potent growth inhibitor to a tumor promoter are not fully understood. We report here that TGF-β directly regulates alternative splicing of cancer stem cell marker CD44 through a phosphorylated T179 of SMAD3-mediated interaction with RNA-binding protein PCBP1. We show that TGF-β and EGF respectively induce SMAD3 and PCBP1 to colocalize in SC35-positive nuclear speckles, and the two proteins interact in the variable exon region of CD44 pre-mRNA to inhibit spliceosome assembly in favor of expressing the mesenchymal isoform CD44s over the epithelial isoform CD44E. We further show that the SMAD3-mediated alternative splicing is essential to the tumor-promoting role of TGF-β and has a global influence on protein products of genes instrumental to epithelial-to-mesenchymal transition and metastasis.
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: Veenu
authors.initials: V
authors.lastname: Tripathi
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Sixt
authors.affiliation: Genetics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: Shaojian
authors.initials: S
authors.lastname: Gao
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: Xuan
authors.initials: X
authors.lastname: Xu
authors.affiliation: Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Huang
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: Roberto
authors.initials: R
authors.lastname: Weigert
authors.affiliation: Laboratory of Protein Characterization, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
authors.affiliation: Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA. Electronic address: zhangyin@mail.nih.gov.
authors.forename: Ying E
authors.initials: YE
authors.lastname: Zhang
mesh_terms: D017398:Alternative Splicing / Q000187:drug effects*; D000818:Animals; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects*; D005091:Exons; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000235:genetics* / Q000378:metabolism; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins; D015398:Signal Transduction; D051900:Smad3 Protein / Q000235:genetics* / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology
chemical_list: C497483:CD44 protein, human; D004268:DNA-Binding Proteins; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D018960:Hyaluronan Receptors; C094604:PCBP1 protein, human; D020033:Protein Isoforms; D012322:RNA Precursors; D016601:RNA-Binding Proteins; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D013912:Threonine; D004815:Epidermal Growth Factor
keywords: CD44; EMT; PCBP1; SMAD3; TGF-β; alternative splicing; metastasis