The Src and Signal Transducers and Activators of Transcription Pathways As Specific Targets for Low Molecular Weight Phosphotyrosine-protein Phosphatase in Platelet-derived Growth Factor Signaling

Abstract

The low molecular weight phosphotyrosine-protein phosphatase (LMW-PTP) is a cytosolic phosphotyrosineprotein phosphatase specifically interacting with the activated platelet-derived growth factor (PDGF) receptor through its active site. Overexpression of the LMW-PTP results in modulation of PDGF-dependent mitogenesis. In this study we investigated the effects of this tyrosine phosphatase on the signaling pathways relevant for PDGF-dependent DNA synthesis. NIH 3T3 cells were stably transfected with active or dominant negative LMW-PTP. The effects of LMW-PTP were essentially restricted to the G 1 phase of the cell cycle. Upon stimulation with PDGF, cells transfected with the dominant negative LMW-PTP showed an increased activation of Src, whereas the active LMW-PTP induced a reduced activation of this proto-oncogene. We observe that c-Src binding to PDGF receptor upon stimulation is prevented by overexpression of LMW-PTP. These effects were associated with parallel changes in myc expression. Moreover, wild-type and dominant negative LMW-PTP differentially regulated STAT1 and STAT3 activation and tyrosine phosphorylation, whereas they did not modify extracellular signal-regulated kinase activity. However, these modifications were associated with changes in fos expression despite the lack of any effect on extracellular signal-regulated kinase activation. Other independent pathways involved in PDGF-induced mitogenesis, such as phosphatidylinositol 3-kinase and phospholipase C-␥1, were not affected by LMW-PTP. These data indicate that this phosphatase selectively interferes with the Src and the STATs pathways in PDGF downstream signaling. The resulting changes in myc and fos proto-oncogene expression are likely to mediate the modifications observed in the G 1 phase of the cell cycle.Protein-tyrosine phosphorylation plays a key role in the regulation of many cellular processes in eukaryotes such as cellular metabolism, proliferation, differentiation, and oncogenic transformation (1). Accumulating evidence indicates that the contribution of phosphotyrosine-protein phosphatases (PTPs) 1 to the control of phosphorylation state is as relevant as that of phosphotyrosine-protein kinases. PTPs activity is carefully regulated and appears to be, in most cases, highly specific. The PTPs consist of a family of over 40 enzymes often classified into three groups: 1) receptor-like PTPs; 2) intracellular PTPs; and 3) dual specificity PTPs (2). All PTPs share the signature active site motif CXXXXXR, in which the catalytic cysteine residue is involved in formation of a phosphoenzyme reaction intermediate (3). The low molecular weight phosphotyrosine-protein phosphatase (LMW-PTP) is a cytosolic enzyme without extensive sequence homology with other PTPs family members, but it contains the CXXXXXR motif and shares the same catalytic mechanism of classical PTPs (4, 5). Furthermore, the LMW-PTP crystal structure (6) revealed a tridimensionally folded phosphate binding loop that is structurally identical to that contained in the human plac...

Ursolic Acid Inhibits STAT3 Activation Pathway Leading to Suppression of Proliferation and Chemosensitization of Human Multiple Myeloma Cells

“…Ursolic acid has been shown to inhibit PTP-1B (50, 51), thus suggesting that PTP-1B is not involved in the dephosphorylation of STAT3. Numerous PTPs have been implicated in STAT3 signaling, including SHP-1, SHP-2, T-cell PTP, PTEN, PTP-1D, CD45, PTPe, and low molecular weight PTP (52)(53)(54)(55)(56)(57)(58)(59)(60). The type of PTP involved in down-regulation of STAT3 phosphorylation is not clear.…”

Two Vicinal Cysteines Confer a Peculiar Redox Regulation to Low Molecular Weight Protein Tyrosine Phosphatase in Response to Platelet-derived Growth Factor Receptor Stimulation

“…It has been reported that the H 2 O 2 produced upon growth factor stimulation is really a cellular second messenger directly influencing many signal transducers such as the STAT proteins, p70 s6k, protein kinase D, and PTPs (33)(34)(35)(36). We have already demonstrated that LMW-PTP is a key regulator of PDGF-R phosphorylation upon recruitment to the membrane when cells are stimulated with the growth factor (5,6,10).…”

“…We have previously shown that activated PDGF-R is a LMW-PTP substrate (4) and that LMW-PTP is involved in the control of specific pathways triggered by PDGF-R activation. In particular, LMW-PTP is able to modulate both myc expression, interfering with the Src pathway, and fos expression through a mitogen-activated protein kinase-independent pathway mediated by the signal transducers and activators of transcription (STAT) proteins (5). More recently, we have found that in NIH3T3 cells LMW-PTP is constitutively localized in both cytoplasmic and cytoskeleton-associated fractions.…”

Differential Regulation of Endothelial Cell Permeability by High and Low Doses of Oxidized 1-Palmitoyl-2-Arachidonyl-sn-Glycero-3-Phosphocholine

“…Interestingly, pretreatment with NAC only partly decreased OxPAPC-induced Src autophosphorylation at Tyr 418 . Previous data demonstrated that the redox-dependent inactivation of low molecular weight protein tyrosine phosphatase (LMW-PTP) was implicated in regulating levels of tyrosine phosphorylation and the activity of signaling kinases, including Src (44)(45)(46), and in controlling cell junction complex integrity (47,48). Thus, we speculate that the ROS-dependent inactivation of LMW-PTP in ECs exposed to high OxPAPC doses may contribute to sustained VE-cadherin phosphorylation via their promotional effects on Src activity, but this ROS-dependent inactivation of LMW-PTP may also stimulate additional mechanisms leading to increased VE-cadherin phosphorylation.…”