epidermal-growth-factor and Noonan-Syndrome

Son of sevenless 1 (SOS1) is a Ras-specific guanine-nucleotide-exchange factor (GEF) that mediates intracellular signaling processes induced by receptor tyrosine kinases. In this study, we show that CIIA (also known as VPS28) physically associates with SOS1 and thereby inhibits the GEF activity of SOS1 on Ras, which prevents the epidermal growth factor (EGF)-induced activation of the Ras-Erk1/2 pathway. Furthermore, CIIA inhibited cyclin D1 expression, as well as DNA, synthesis in response to EGF. Intriguingly, CIIA failed to inhibit the Ras-specific GEF activity of Noonan-syndrome-associated SOS1 mutants (M269R, R552G, W729L and E846K). Taken together, our results suggest that CIIA functions as a negative modulator of the SOS1-Ras signaling events initiated by peptide growth factors including EGF.

Topics: Animals; Cyclin D1; DNA Replication; Dogs; Endosomal Sorting Complexes Required for Transport; Epidermal Growth Factor; Extracellular Signal-Regulated MAP Kinases; Guanine Nucleotide Exchange Factors; HEK293 Cells; HeLa Cells; Humans; Madin Darby Canine Kidney Cells; MAP Kinase Signaling System; Mice; Mutation, Missense; NIH 3T3 Cells; Noonan Syndrome; ras Proteins; SOS1 Protein

Noonan syndrome is a developmental disorder with dysmorphic facies, short stature, cardiac defects, and skeletal anomalies, which can be caused by missense PTPN11 mutations. PTPN11 encodes Src homology 2 domain-containing tyrosine phosphatase 2 (SHP2 or SHP-2), a protein tyrosine phosphatase that acts in signal transduction downstream to growth factor, hormone, and cytokine receptors. We compared the functional effects of three Noonan syndrome-causative PTPN11 mutations on SHP2's phosphatase activity, interaction with a binding partner, and signal transduction. All SHP2 mutants had significantly increased basal phosphatase activity compared to wild type, but that activity varied significantly between mutants and was further increased after epidermal growth factor stimulation. Cells expressing SHP2 mutants had prolonged extracellular signal-regulated kinase 2 activation, which was ligand-dependent. Binding of SHP2 mutants to Grb2-associated binder-1 was increased and sustained, and tyrosine phosphorylation of both proteins was prolonged. Coexpression of Grb2-associated binder-1-FF, which lacks SHP2 binding motifs, blocked the epidermal growth factor-mediated increase in SHP2's phosphatase activity and resulted in a dramatic reduction of extracellular signal-regulated kinase 2 activation. Taken together, these results document that Noonan syndrome-associated PTPN11 mutations increase SHP2's basal phosphatase activity, with greater activation when residues directly involved in binding at the interface between the N-terminal Src homology 2 and protein tyrosine phosphatase domains are altered. The SHP2 mutants prolonged signal flux through the RAS/mitogen-activated protein kinase (ERK2/MAPK1) pathway in a ligand-dependent manner that required docking through Grb2-associated binder-1 (GAB1), leading to increased cell proliferation.

Topics: Adaptor Proteins, Signal Transducing; Animals; Antigen-Antibody Complex; Cell Division; Cell Line; Chlorocebus aethiops; CHO Cells; COS Cells; Cricetinae; Enzyme Activation; Epidermal Growth Factor; Humans; Intracellular Signaling Peptides and Proteins; MAP Kinase Signaling System; Mitogen-Activated Protein Kinases; Mutagenesis, Site-Directed; Mutation; Noonan Syndrome; Phosphoproteins; Protein Binding; Protein Phosphatase 2; Protein Structure, Quaternary; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Protein Tyrosine Phosphatases; SH2 Domain-Containing Protein Tyrosine Phosphatases; src Homology Domains