Low molecular weight protein tyrosine phosphatases: small, but smart.
ABSTRACT Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are a family of 18-kDa enzymes involved in cell growth regulation. Despite very limited sequence similarity to the PTP superfamily, they display a conserved signature motif in the catalytic site. LMW-PTP associates and dephosphorylate many growth factor receptors, such as platelet-derived growth factor receptor (PDGF-r), insulin receptor and ephrin receptor, thus downregulating many of the tyrosine kinase receptor functions that lead to cell division. In particular, LMW-PTP acts on both growth-factor-induced mitosis, through dephosphorylation of activated PDGF-r, and on cytoskeleton rearrangement, through dephosphorylation of p190RhoGAP and the consequent regulation of the small GTPase Rho. LMW-PTP activity is modulated by tyrosine phosphorylation on two specific residues, each of them with specific characteristics. LMW-PTP activity on specific substrates depends also on its localization. Moreover, LMW-PTP is reversibly oxidized during growth factor signaling, leading to inhibition of its enzymatic activity. Recovery of phosphatase activity depends on the availability of reduced glutathione and involves the formation of an S-S bridge between the two catalytic site cysteines. Furthermore, studies on the redox state of LMW-PTP in contact-inhibited cells and in mature myoblasts suggest that LMW-PTP is a general and versatile modulator of growth inhibition.
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ABSTRACT: Protein tyrosine phosphatases (PTPs) play a critical role in physiological signaling pathways by controlling the level of tyrosine phosphorylation. The past decade has seen a vast increase in both academic and industrial interest in PTPs and their relevance as potential therapeutic targets, with several PTP inhibitors recently entering clinical trials. Despite these developments, there are numerous examples of failed PTP drug discovery programs, such that PTPs have attained a reputation as 'undruggable' targets. This review attempts to illustrate the many obstacles that must be overcome to successfully develop a PTP drug, ranging from validation of PTPs as therapeutic targets to the difficulties of assessing the true inhibitory nature of apparently well-behaved compounds, along with the need to balance the physiocochemical properties required for active site binding with the characteristics needed for in vivo activity. A number of examples of structure-based design are presented, along with cautionary tales of PTP inhibitor programs that have failed due to unexpected shortcomings.Current Medicinal Chemistry 02/2009; 16(17):2095-176. · 4.86 Impact Factor
Article: Proteome analysis of the sarcoplasmic fraction of pig semimembranosus muscle: implications on meat color development.[show abstract] [hide abstract]
ABSTRACT: Two-dimensional electrophoresis was used to investigate sarcoplasmic protein expression in pig Semimembranosus muscles sampled 20 min after slaughter. Two groups (light and dark) of 12 animals were selected from 1000 pigs, based on meat L values measured 36 h postmortem. Twenty-two proteins or fragments (p < 0.05) were differentially expressed. Muscles leading to darker meat had a more oxidative metabolism, indicated by more abundant mitochondrial enzymes of the respiratory chain, hemoglobin, and chaperone or regulator proteins (HSP27, alphaB-crystallin, and glucose-regulated protein 58 kDa). Conversely, enzymes of glycolysis were overexpressed in the lighter group. Such samples were also characterized by higher levels of glutathione S-transferase omega, which can activate the RyR calcium channels, and higher levels of cyclophilin D. This protein pattern is likely to have severe implications on postmortem metabolism, namely, acceleration of ATP depletion and pH fall and subsequent enhanced protein denaturation, well-known to induce discoloration.Journal of Agricultural and Food Chemistry 04/2006; 54(7):2732-7. · 2.82 Impact Factor
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ABSTRACT: Tyrosine phosphorylation is an important signalling mechanism in eukaryotic cells. In cancer, oncogenic activation of tyrosine kinases is a common feature, and novel anticancer drugs have been introduced that target these enzymes. Tyrosine phosphorylation is also controlled by protein-tyrosine phosphatases (PTPs). Recent evidence has shown that PTPs can function as tumour suppressors. In addition, some PTPs, including SHP2, positively regulate the signalling of growth-factor receptors, and can be oncogenic. An improved understanding of how these enzymes function and how they are regulated might aid the development of new anticancer agents.Nature reviews. Cancer 05/2006; 6(4):307-20. · 37.54 Impact Factor