Low Molecular Weight Protein-tyrosine Phosphatase Is Involved in Growth Inhibition during Cell Differentiation

Abstract

Low molecular weight protein-tyrosine phosphatase (LMW-PTP) is an enzyme involved in mitogenic signaling and cytoskeletal rearrangement after platelet-derived growth factor (PDGF) stimulation. Recently, we demonstrated that LMW-PTP is regulated by a redox mechanism involving the two cysteine residues of the catalytic site, which turn reversibly from reduced to oxidized state after PDGF stimulation. Since recent findings showed a decrease of intracellular reactive oxygen species in contact inhibited cells and a lower tyrosine phosphorylation level in dense cultures in comparison to sparse ones, we studied if the level of endogenous LMW-PTP is regulated by growth inhibition conditions, such as cell confluence and differentiation. Results show that both cell confluence and cell differentiation up-regulate LMW-PTP expression in C2C12 and PC12 cells. We demonstrate that during myogenesis LMW-PTP is regulated at translational level and that the protein accumulates at the plasma membrane. Furthermore, we showed that both myogenesis and cell-cell contact lead to a dramatical decrease of tyrosine phosphorylation level of PDGF receptor. In addition, we observed an increased association of the receptor with LMW-PTP during myogenesis. Herein, we demonstrate that myogenesis decreases the intracellular level of reactive oxygen species, as observed in dense cultures. As a consequence, LMW-PTP turns from oxidized to reduced form during muscle differentiation, increasing its activity in growth inhibition conditions such as differentiation. These data suggest that LMW-PTP plays a crucial role in physiological processes, which require cell growth arrest such as confluence and differentiation.The control of protein tyrosine phosphorylation in vivo is regulated by the coordinated and competing actions of proteintyrosine kinases and protein-tyrosine phosphatases (PTPs) 1 (1). PTPs have been identified in eukaryotes, prokaryotes, plants, and virus and comprise a large family of enzymes, that rival protein-tyrosine kinases in structural diversity and complexity (2). PTPs may either antagonize or potentiate proteintyrosine kinase-induced signaling in vivo and have been implicated in fundamental physiological processes such as growth and proliferation, differentiation, and cytoskeletal functions (3). Most growth factors, when bind to their receptors, activate an intracellular cascade of events involving tyrosine phosphorylation of the receptor itself and of several other substrates, phosphotyrosine-dependent recruitment of multiple signal transducers to the cell membrane and, eventually, the delivery of mitogenic stimuli (4). With some exceptions, PTPs exert a general inhibitory effect on this intracellular cascade by attenuating the intensity of phosphorylation signals initiated by activated receptors and accelerating their extinction (2).LMW-PTP is an 18-kDa enzyme widely distributed in mammalian tissues (5). Previous findings demonstrated that PDGFr is an in vivo substrate of LMW-PTP and that this protein is involved in the control of...

Regulation of the EphA2 Kinase by the Low Molecular Weight Tyrosine Phosphatase Induces Transformation

“…Notably, however, LMW-PTP-overexpressing MCF-10A epithelial cells displayed reduced rates of cell growth as measured using two-dimensional assays of cell growth. This latter observation is consistent with recent reports that high levels of LMW-PTP similarly decrease the monolayer growth rates of other cell types (30,31). Although such a finding had been interpreted to suggest that LMW-PTP might negatively regulate transformation, our findings support a very different conclusion.…”

H2O2-dependent Activation of GCLC-ARE4 Reporter Occurs by Mitogen-activated Protein Kinase Pathways without Oxidation of Cellular Glutathione or Thioredoxin-1

“…Rhee and colleagues showed that protein-tyrosine phosphatase 1B (PTP1B) is inactivated by ROS, which is produced in response to growth factors, and that this involves oxidation of a low pK a cysteine in the active site of the enzyme (47). A low molecular weight tyrosine phosphatase is inactivated in a similar manner by H 2 O 2 (48). Inactivation of one or multiple tyrosine phosphatases by this mechanism results in markedly increased tyrosine phosphate levels, for example, in response to EGF (49).…”

Gene expression profiles in cells transformed by overexpression of the IGF-I receptor

“…The greatest difference in expression (five-fold higher in R þ cells) was observed with PKCd-binding protein (Izumi et al, 1997) (Figure 3). Low Molecular Weight-Protein Tyrosine Phosphatase (Lmw-ptp), which can negatively regulate growth (Fiaschi et al, 2001), was expressed almost four-fold more in R þ cells (Figure 3). The early response zinc-finger protein tis11D (Varnum et al, 1991) was three-fold more abundant in R þ cells than in R À cells (Figure 3).…”