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.
Keywords:
CD44; EMT; PCBP1; SMAD3; TGF-β; alternative splicing; metastasis.
Published by Elsevier Inc.
MeSH terms
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Alternative Splicing / drug effects*
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Animals
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Cell Line, Tumor
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DNA-Binding Proteins
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Epidermal Growth Factor / metabolism
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Epidermal Growth Factor / pharmacology
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Epithelial-Mesenchymal Transition / drug effects*
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Exons
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Female
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Gene Expression Profiling
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Gene Expression Regulation, Neoplastic*
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Heterogeneous-Nuclear Ribonucleoproteins / genetics*
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Heterogeneous-Nuclear Ribonucleoproteins / metabolism
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Humans
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Hyaluronan Receptors / genetics*
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Hyaluronan Receptors / metabolism
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Lung Neoplasms / genetics*
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Lung Neoplasms / metabolism
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Lung Neoplasms / pathology
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Mice
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Mice, Nude
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Neoplasm Transplantation
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Neoplastic Stem Cells / drug effects
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Neoplastic Stem Cells / metabolism
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Neoplastic Stem Cells / pathology
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Phosphorylation / drug effects
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Promoter Regions, Genetic
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Protein Isoforms / genetics
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Protein Isoforms / metabolism
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RNA Precursors / genetics
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RNA Precursors / metabolism
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RNA-Binding Proteins
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Signal Transduction
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Smad3 Protein / genetics*
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Smad3 Protein / metabolism
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Threonine / metabolism
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Transforming Growth Factor beta / metabolism
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Transforming Growth Factor beta / pharmacology
Substances
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CD44 protein, human
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DNA-Binding Proteins
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Heterogeneous-Nuclear Ribonucleoproteins
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Hyaluronan Receptors
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PCBP1 protein, human
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Protein Isoforms
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RNA Precursors
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RNA-Binding Proteins
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SMAD3 protein, human
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Smad3 Protein
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Transforming Growth Factor beta
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Threonine
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Epidermal Growth Factor