Abstract
In an attempt to identify the cell-associated protein(s) through which SMOC (Secreted Modular Calcium binding protein) induces mitogen-activated protein kinase (MAPK) signaling, the epidermal growth factor receptor (EGFR) became a candidate. However, although in 32D/EGFR cells, the EGFR was phosphorylated in the presence of a commercially available human SMOC-1 (hSMOC-1), only minimal phosphorylation was observed in the presence of Xenopus SMOC-1 (XSMOC-1) or human SMOC-2. Analysis of the commercial hSMOC-1 product demonstrated the presence of pro-EGF as an impurity. When the pro-EGF was removed, only minimal EGFR activation was observed, indicating that SMOC does not signal primarily through EGFR and its receptor remains unidentified. Investigation of SMOC/pro-EGF binding affinity revealed a strong interaction that does not require the C-terminal extracellular calcium-binding (EC) domain of SMOC or the EGF domain of pro-EGF. SMOC does not appear to potentiate or inhibit MAPK signaling in response to pro-EGF, but the interaction could provide a mechanism for retaining soluble pro-EGF at the cell surface.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Animals
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Binding Sites
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Calcium-Binding Proteins / genetics
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Calcium-Binding Proteins / metabolism
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Embryo, Nonmammalian
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Epidermal Growth Factor / genetics
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Epidermal Growth Factor / metabolism*
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ErbB Receptors / genetics
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ErbB Receptors / metabolism
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Escherichia coli / genetics
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Escherichia coli / metabolism
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Gene Expression Regulation
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HEK293 Cells
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Humans
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Mitogen-Activated Protein Kinase 1 / genetics
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Mitogen-Activated Protein Kinase 1 / metabolism*
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Mitogen-Activated Protein Kinase 3 / genetics
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Mitogen-Activated Protein Kinase 3 / metabolism*
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Osteonectin / genetics
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Osteonectin / metabolism*
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Phosphorylation
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Protein Binding
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Protein Interaction Domains and Motifs
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Protein Precursors / genetics
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Protein Precursors / metabolism*
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Signal Transduction
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Species Specificity
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Xenopus Proteins / genetics
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Xenopus Proteins / metabolism*
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Xenopus laevis / embryology
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Xenopus laevis / genetics
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Xenopus laevis / metabolism*
Substances
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Calcium-Binding Proteins
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Osteonectin
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Protein Precursors
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Recombinant Proteins
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SMOC1 protein, Xenopus
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SMOC1 protein, human
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SMOC2 protein, human
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Xenopus Proteins
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epidermal growth factor precursor
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Epidermal Growth Factor
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ErbB Receptors
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
Grants and funding
All funding for this study was FDA intramural funding. No grants were received.