Abstract
LEOPARD syndrome (LS), a disorder with multiple developmental abnormalities, is mainly due to mutations that impair the activity of the tyrosine phosphatase SHP2 (PTPN11). How these alterations cause the disease remains unknown. We report here that fibroblasts isolated from LS patients displayed stronger epidermal growth factor (EGF)-induced phosphorylation of both AKT and glycogen synthase kinase 3beta (GSK-3beta) than fibroblasts from control patients. Similar results were obtained in HEK293 cells expressing LS mutants of SHP2. We found that the GAB1/phosphoinositide 3-kinase (PI3K) complex was more abundant in fibroblasts from LS than control subjects and that both AKT and GSK-3beta hyperphosphorylation were prevented by reducing GAB1 expression or by overexpressing a GAB1 mutant unable to bind to PI3K. Consistently, purified recombinant LS mutants failed to dephosphorylate GAB1 PI3K-binding sites. These mutants induced PI3K-dependent increase in cell size in a model of chicken embryo cardiac explants and in transcriptional activity of the atrial natriuretic factor (ANF) gene in neonate rat cardiomyocytes. In conclusion, SHP2 mutations causing LS facilitate EGF-induced PI3K/AKT/GSK-3beta stimulation through impaired GAB1 dephosphorylation, resulting in deregulation of a novel signaling pathway that could be involved in LS pathology.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing / genetics
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Adaptor Proteins, Signal Transducing / metabolism
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Animals
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Atrial Natriuretic Factor / genetics
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Atrial Natriuretic Factor / metabolism
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Cells, Cultured
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Chick Embryo
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Enzyme Activation
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Epidermal Growth Factor / metabolism*
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Fibroblasts / cytology
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Fibroblasts / physiology
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Glycogen Synthase Kinase 3 / genetics
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Glycogen Synthase Kinase 3 / metabolism*
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Glycogen Synthase Kinase 3 beta
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Humans
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LEOPARD Syndrome* / genetics
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LEOPARD Syndrome* / metabolism
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LEOPARD Syndrome* / pathology
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Mutation
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Myocytes, Cardiac / cytology
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Myocytes, Cardiac / physiology
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Phosphatidylinositol 3-Kinases / genetics
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Phosphatidylinositol 3-Kinases / metabolism*
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Phosphorylation
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Protein Tyrosine Phosphatase, Non-Receptor Type 11 / genetics
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Protein Tyrosine Phosphatase, Non-Receptor Type 11 / metabolism*
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Proto-Oncogene Proteins c-akt / genetics
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Proto-Oncogene Proteins c-akt / metabolism*
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RNA, Small Interfering / genetics
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RNA, Small Interfering / metabolism
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Rats
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Signal Transduction / physiology*
Substances
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Adaptor Proteins, Signal Transducing
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GAB1 protein, human
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RNA, Small Interfering
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Recombinant Fusion Proteins
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Epidermal Growth Factor
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Atrial Natriuretic Factor
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Phosphatidylinositol 3-Kinases
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GSK3B protein, human
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Glycogen Synthase Kinase 3 beta
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Gsk3b protein, rat
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Proto-Oncogene Proteins c-akt
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Glycogen Synthase Kinase 3
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Protein Tyrosine Phosphatase, Non-Receptor Type 11