PDGF receptor as a specific in vivo target for low M_r phosphotyrosine protein phosphatase

Abstract

Low M r phosphotyrosine protein phosphatase (LMW-PTP) is a 18 kDa cytosolic enzyme widely distributed in eukaryotic cells. LMW-PTP catalyses the hydrolysis of phosphotyrosine residues and overexpression of the enzyme in normal and transformed cells inhibits cell proliferation. Site directed mutagenesis, together with crystallographic studies, have contributed to clarify the catalytic mechanism, which involves the active site signature sequence Ci2XXXXXRts , a main feature of all PTPase family members. In order to identify the LMW-PTP substrate/s we have expressed in NIH-3T3 cells a catalytically inert Cys 12 to Ser phosphatase mutant which has preserved its capacity for substrate binding. Overexpression of the mutant phosphatase leads to enhanced cell proliferation and serum induced mitogenesis, indicating that the mutation results in the production of a dominant negative protein. Analysis of mutant LMW-PTP expressing cells has enabled us to demonstrate an association between LMW-PTP and platelet derived growth factor receptor that appears to be highly specific. Our data suggest a catalytic action of LMW-PTP on the phosphorylated platelet derived growth factor receptor.

In vivo inactivation of phosphotyrosine protein phosphatases by nitric oxide

“…In fact, the level of phosphotyrosine in BB-PDGF-stimulated NIH/3T3 fibroblasts overexpressing this enzyme is strongly reduced with respect to normal cells [19]. In addition, we found that a dominant negative gene (which produce a catalytically inactive enzyme that is still able to bind substrates) overexpressed in the above cell line forms a complex with the PDGF receptor [20].…”

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

“…The first point that we addressed was the in vitro behavior of LMW-PTP overexpressing cells. Previously reported data on PDGF-induced mitogenesis indicated LMW-PTP as a negative regulator of cell proliferation, although it positively influences integrinmediated cell motility (Chiarugi et al, 1995(Chiarugi et al, , 2000bRaugei et al, 2002). In addition, very recently it has been reported that LMW-PTP increases cadherinmediated cell-cell adhesions, leading to adherens junction strengthening (Taddei et al, 2002).…”

“…LMW-PTP has been shown to interact with several receptor tyrosine kinases and docking proteins, including platelet-derived growth factor receptor (PDGF-R) (Chiarugi et al, 1995), ephrin A2 receptor (Eph2A) (Kikawa et al, 2002), and b-catenin (Taddei et al, 2002). LMW-PTP has been largely considered a negative regulator of growth factor-induced cell proliferation, although in some instances it functions as a positive device.…”

DHEA attenuates PDGF-induced phenotypic proliferation of vascular smooth muscle A7r5 cells through redox regulation

“…A number of tyrosine residues are phosphorylated in the cytosolic domain of PDGFR, leading to a site-specific recruitment of signal transduction molecules [4]. PTPs such as LMW-PTP are implicated in the control of PDGFR phosphorylation [16]. LMW-PTP is an 18-kDa enzyme that is widely expressed [17].…”