The 18 kDa cytosolic acid phosphatase from bovine liver has phosphotyrosine phosphatase activity on the autophosphorylated epidermal growth factor receptor

Abstract

In this paper we demonstrate that the cytosolic low-M~ acid phosphatase purified from bovine liver has phosphotyrosine protein phosphatase acitivity on aep-autophosphorylated epidermal growth factor (EGF) receptor. This activity was significantly inhibited by orthovanadate and p-hydroxymercuribenzoate; the latter result indicates that free sulfhydryl groups are required for phosphotyrosine phosphatase activity. The enzyme was active in a broad pH range, with maximum activity between pH 5.5 and 7.5. The apparent Km for 32P-EGF receptor dephosphorylation was 4 riM. The enzyme appeared to be specific for phosphotyrosine in that it dephosphorylated the autophosphorylated EGF receptor and L-phosphotyrosine, but not a2P-Ser-casein, L-phosphoserine or L-phosphothreonine. These data suggest that the cytosolic low-Mr acid phosphatase might play a regulatory role in EGF receptor-dependent transmembrane signalling.Acid phosphatase; Epidermal growth factor receptor; Phosphotyrosine

Inhibition of cellular response to platelet‐derived growth factor by low Mr phosphotyrosine protein phosphatase overexpression

“…Therefore, the localization of PTPase was not altered by the level of expression, and the distribution was not changed by growth factor stimulation. The demonstrated activity of this PTPase on the autophosphorylated EGF receptor in vitro [26], together with the specific dephosphorylation of the PDGF receptor in vivo, point to a direct action of this cytosolic PTPase on a membrane substrate.…”

“…The low M, PTPase dephosphorylates the tyrosineautophosphorylated epidermal growth factor receptor in vitro [26] and inhibits the growth of NIH/3T3 cells transformedbyv-erbB [22]andbyotherdifferentoncogenes [23].…”

LMW-PTP is a positive regulator of tumor onset and growth

“…By means of wt and dnLMW-PTP overexpression, we and others suggest both negative and positive roles for LMW-PTP. In particular, in in vitro cell cultures LMW-PTP negatively influences PDGF-R (Chiarugi et al, 1995), fibroblast growth factor receptor (Rigacci et al, 1999), epidermal growth factor receptor (Ramponi et al, 1989) and insulin receptor signaling (Chiarugi et al, 1997), and positively affects EphA2 (Kikawa et al, 2002) and EphB1 signaling (Stein et al, 1998). Similar to LMW-PTP, SHP-2 has been proposed for both a positive and negative role in signal transduction (Ronnstrand and Heldin, 2001).…”

Aspartic‐129 is an essential residue in the catalytic mechanism of the low Mr phosphotyrosine protein phosphatase

“…These isoforms have been sequenced from varying sources [2~l], and the crystal structure of the bovine liver enzyme (belonging to type 2) has been recently determined [25]. The low Mr PTPase catalyses the hydrolysis of arylphosphates [5], including phosphotyrosine, as well as of phosphotyrosine containing peptides and proteins [6,7] of great biological interest. The low Mr PTPase does not elicit any sequence homology to other members of the PTPase family; however, it displays the active-site signature motif CXXXXXR common to all PTPases [8].…”