title: Receptor-type protein-tyrosine phosphatase-kappa regulates epidermal growth factor receptor function.
abstract: Epidermal growth factor receptor (EGFR), the prototypic receptor protein tyrosine kinase, is a major regulator of growth and survival for many epithelial cell types. We report here that receptor-type protein-tyrosine phosphatase-kappa (RPTP-kappa) dephosphorylates EGFR and thereby regulates its function in human keratinocytes. Protein-tyrosine phosphatase (PTP) inhibitors induced EGFR tyrosine phosphorylation in intact primary human keratinocytes and cell-free membrane preparations. Five highly expressed RPTPs (RPTP-beta, delta, kappa, mu, and xi) were functionally analyzed in a Chinese hamster ovary (CHO) cell-based expression system. Full-length human EGFR expressed in CHO cells, which lack endogenous EGFR, displayed high basal (i.e. in the absence of ligand) tyrosine phosphorylation. Co-expression of RPTP-kappa, but not other RPTPs, specifically reduced basal EGFR tyrosine phosphorylation. RPTP-kappa also reduced epidermal growth factor-dependent EGFR tyrosine phosphorylation in CHO cells. Purified RPTP-kappa preferentially dephosphorylated EGFR tyrosines 1068 and 1173 in vitro. Overexpression of wild-type or catalytically inactive RPTP-kappa reduced or enhanced, respectively, basal and EGF-induced EGFR tyrosine phosphorylation in human keratinocytes. Furthermore, siRNA-mediated knockdown of RPTP-kappa increased basal and EGF-stimulated EGFR tyrosine phosphorylation and augmented downstream Erk activation in human keratinocytes. RPTP-kappa levels increased in keratinocytes as cells reached confluency, and overexpression of RPTP-kappa in subconfluent keratinocytes reduced keratinocyte proliferation. Taken together, the above data indicate that RPTP-kappa is a key regulator of EGFR tyrosine phosphorylation and function in human keratinocytes.
authors.affiliation: Department of Dermatology, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Yiru
authors.initials: Y
authors.lastname: Xu
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Tan
authors.forename: Vladimir
authors.initials: V
authors.lastname: Grachtchouk
authors.forename: John J
authors.initials: JJ
authors.lastname: Voorhees
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Fisher
mesh_terms: D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D006224:Cricetinae; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology; D066246:ErbB Receptors / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005822:Genetic Vectors; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000378:metabolism; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection; D014443:Tyrosine / Q000737:chemistry
chemical_list: D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D014443:Tyrosine; D005982:Glutathione Transferase; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; C489852:PTPRK protein, human; D017027:Protein Tyrosine Phosphatases; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2