Abstract
MUC4: encodes a large transmembrane mucin that is overexpressed in pancreatic adenocarcinomas. The molecular mechanisms responsible for that altered pattern of expression are unknown. TGF-beta, a pleiotropic cytokine, regulates numerous genes involved in pancreatic carcinogenesis via activation of the Smads proteins and MUC4 promoter is rich in Smad-binding elements. Our aim was to study whether the regulation of MUC4 expression by TGF-beta in pancreatic cancer cells was strictly dependent on Smad4 activity. Three pancreatic cancer cell lines, CAPAN-1 (MUC4+/Smad4-), CAPAN-2 (MUC4+/Smad4+) and PANC-1 (MUC4-/Smad4+), were used. By RT-PCR, transfection assays and immunohistochemistry, we show that (i) both MUC4 mRNA and apomucin expression are upregulated by TGF-beta, (ii) Smad2 positively cooperates with Smad4 to activate the promoter, (iii) activation of Smad4 by exogenous TGF-beta induces Smad4 binding to the promoter, (iv) Smad7 and c-ski both inhibit activation by Smad4. When Smad4 is mutated and inactive, TGF-beta activates MUC4 expression via MAPK, PI3K and PKA signaling pathways. Absence of expression in PANC-1 cells is due to histone deacetylation. Altogether, these results indicate that upregulation of MUC4 by TGF-beta is restricted to well-differentiated pancreatic cancer cells, and point out a novel mechanism for TGF-beta as a key molecule in targeting MUC4 overexpression in pancreatic adenocarcinomas.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Cyclic AMP-Dependent Protein Kinases / metabolism
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism
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Enzyme Inhibitors / pharmacology
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Gastric Mucins / genetics
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Gastric Mucins / metabolism
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Gene Expression Regulation, Neoplastic / drug effects
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Histones / metabolism
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Humans
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Ligands
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Mitogen-Activated Protein Kinase 1 / antagonists & inhibitors
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mucin-4
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Mucins / genetics*
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Mucins / metabolism
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Pancreatic Neoplasms / genetics*
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Pancreatic Neoplasms / pathology
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Phosphatidylinositol 3-Kinases / metabolism
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Phosphoinositide-3 Kinase Inhibitors
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Promoter Regions, Genetic
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Protein Kinase C / metabolism
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Receptor, ErbB-2 / genetics
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Receptor, ErbB-2 / metabolism*
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Regulatory Sequences, Nucleic Acid
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Signal Transduction
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Smad2 Protein
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Smad4 Protein
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Trans-Activators / genetics
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Trans-Activators / metabolism
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Transforming Growth Factor beta / metabolism*
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Transforming Growth Factor beta / pharmacology
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Tumor Cells, Cultured
Substances
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DNA-Binding Proteins
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Enzyme Inhibitors
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Gastric Mucins
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Histones
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Ligands
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MUC4 protein, human
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Mucin-4
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Mucins
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Phosphoinositide-3 Kinase Inhibitors
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SMAD2 protein, human
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SMAD4 protein, human
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Smad2 Protein
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Smad4 Protein
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Trans-Activators
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Transforming Growth Factor beta
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apomucin
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Receptor, ErbB-2
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Cyclic AMP-Dependent Protein Kinases
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Protein Kinase C
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Mitogen-Activated Protein Kinase 1