Oncogenic HRAS mutations cause prolonged PI3K signaling in response to epidermal growth factor in fibroblasts of patients with Costello syndrome.
Costello syndrome (CS) is a rare congenital disorder characterized by failure to thrive, craniofacial dysmorphisms, cardiac and skin abnormalities, mental retardation, and predisposition to malignancies. CS is caused by heterozygous gain-of-function mutations in HRAS that also occur as somatic alterations in human tumors. HRAS is one of the three classical RAS proteins and cycles between an active, GTP- and an inactive, GDP-bound conformation. We used primary human skin fibroblasts from patients with CS as a model system to study the functional consequences of HRAS mutations on endogenous signaling pathways. The GTP-bound form of HRAS was significantly enriched in CS compared with normal fibroblasts. Active HRAS is known to stimulate both the RAF-MEK-ERK and the PI3K-AKT signaling cascade. Phosphorylation of MEK and ERK was normal in CS fibroblasts under basal conditions and slightly prolonged after epidermal growth factor (EGF) stimulation. Interestingly, basal phosphorylation of AKT was increased yet more in CS fibroblasts. Moreover, AKT phosphorylation was diminished in the early and enhanced in the late phase of EGF stimulation. Taken together, these results document that CS-associated HRAS mutations result in prolonged signal flux in a ligand-dependent manner. Our data suggest that altered cellular response to growth factors rather than constitutive activation of HRAS downstream signaling molecules may contribute to some of the clinical features in patients with CS.
Rosenberger
Georg
G
Institut für Humangenetik, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany.
Meien
Stefanie
S
Kutsche
Kerstin
K
D000015:Abnormalities, Multiple / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D019465:Craniofacial Abnormalities; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005183:Failure to Thrive / Q000473:pathology; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008607:Intellectual Disability / Q000473:pathology; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D012867:Skin / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D012868:Skin Abnormalities; D013577:Syndrome
D002867:Chromones; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D006160:Guanosine Triphosphate; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D016283:Proto-Oncogene Proteins p21(ras); C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C482128:MAP2K2 protein, human; C501009:HRAS protein, human