title: Aging-related attenuation of EGF receptor signaling is mediated in part by increased protein tyrosine phosphatase activity.
abstract: As fibroblasts near senescence, their responsiveness to external signals diminishes. This well-documented phenomenon likely underlies physiological deterioration and limited tissue regeneration in aging individuals. Understanding the underlying molecular mechanisms would provide opportunities to ameliorate these situations. A key stimulus for human dermal fibroblasts are ligands for the epidermal growth factor receptor (EGFR). We have shown earlier that EGFR expression decreases by about half in near senescent fibroblasts (Shiraha et al., 2000, J. Biol. Chem. 275 (25), 19343-19351). However, as the cell responses are nearly absent near senescence, other aging-related signal attenuation changes must also occur. Herein, we show that EGFR signaling as determined by receptor autophosphorylation is diminished over 80%, with a corresponding decrease in the phosphorylation of the immediate postreceptor adaptor Shc. Interestingly, we found that this was due at least in part to increased dephosphorylation of EGFR. The global cell phosphotyrosine phosphatase activity increased some threefold in near senescent cells. An initial survey of EGFR-associated protein tyrosine phosphatases (PTPases) showed that SHP-1 (PTPIC, HCP, SHPTP-1) and PTPIB levels are increased in parallel in these cells. Concomitantly, we also discovered an increase in expression of receptor protein tyrosine phosphatase alpha (RPTPalpha). Last, inhibition of protein tyrosine phosphatases by sodium orthovanadate in near senescent cells resulted in increased EGFR phosphorylation. These data support a model in which, near senescence, dermal fibroblasts become resistant to EGFR-mediated stimuli by a combination of receptor downregulation and increased signal attenuation.
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D002460:Cell Line; D016922:Cellular Senescence / Q000502:physiology*; D015536:Down-Regulation / Q000502:physiology; D066246:ErbB Receptors / Q000378:metabolism*; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D007231:Infant, Newborn; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4; D011956:Receptors, Cell Surface; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction / Q000502:physiology*; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D015854:Up-Regulation / Q000502:physiology*; D014638:Vanadates / Q000494:pharmacology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D047908:Intracellular Signaling Peptides and Proteins; D011956:Receptors, Cell Surface; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014638:Vanadates; D066246:ErbB Receptors; C509249:PTPN6 protein, human; C516841:PTPRA protein, human; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4