title: Characterization of a membrane-associated phosphotyrosyl protein phosphatase from the A431 human epidermoid carcinoma cell line.
abstract: The A431 human epidermoid carcinoma cell line exhibits a 30-100-fold overexpression of the epidermal growth factor (EGF) receptor. We have characterized a membrane-associated phosphotyrosyl-protein phosphatase (PTPase) in these cells since it seemed reasonable that overexpression of the EGF-receptor tyrosine kinase will be matched by high PTPase activity. Indeed, of 12 cell lines tested, the A431 cells had the highest specific PTPase activity. About 70% of the total cellular PTPase activity was found associated with membranes after cell fractionation. The membrane-associated PTPase was hydrophobic as judged by its behaviour in Triton X-114 phase partitioning. High-performance liquid chromatography (HPLC) on a DEAE column revealed a single, homogeneous species of membrane-associated PTPase with an apparent molecular mass of 43 kDa as determined by HPLC on a gel permeation column in the presence of Triton X-100. Comparison of this PTPase with the membrane-associated PTPase activities present in rat spleen and in the human chronic myelogenous leukemia cell line K562 revealed additional species resolvable by DEAE-HPLC. These findings suggest that cells may possess different PTPase activities depending on their growth and differentiation states.
authors.affiliation: Ludwig Institute for Cancer Research, Inselspital, Bern, Switzerland.
authors.forename: M T
authors.initials: MT
authors.lastname: Bütler
authors.forename: A
authors.initials: A
authors.lastname: Ziemiecki
authors.forename: B
authors.initials: B
authors.lastname: Groner
authors.forename: R R
authors.initials: RR
authors.lastname: Friis
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases; D051381:Rats; D013154:Spleen / Q000166:cytology / Q000201:enzymology; D014407:Tumor Cells, Cultured
chemical_list: D008565:Membrane Proteins; D066246:ErbB Receptors; D010749:Phosphoprotein Phosphatases; D017027:Protein Tyrosine Phosphatases