There are many misconceptions surrounding the roles of protein phosphatases in the regulation of signal transduction, perhaps the most damaging of which is the erroneous view that these enzymes exert ...their effects merely as constitutively active housekeeping enzymes. On the contrary, the phosphatases are critical, specific regulators of signalling in their own right and serve an essential function, in a coordinated manner with the kinases, to determine the response to a physiological stimulus. This review is a personal perspective on the development of our understanding of the protein tyrosine phosphatase family of enzymes. I have discussed various aspects of the structure, regulation and function of the protein tyrosine phosphatase family, which I hope will illustrate the fundamental importance of these enzymes in the control of signal transduction.
The protein tyrosine phosphatases (PTPs) are critical, specific regulators of signaling in their own right and serve an essential function, in a coordinated manner with the protein tyrosine kinases, to determine the response to a physiological stimulus. In this review I have discussed various aspects of the structure, regulation and function of the PTP family, which I hope will illustrate the fundamental importance of these enzymes to the control of signal transduction
The protein tyrosine phosphatase (PTP) superfamily of enzymes functions in a coordinated manner with protein tyrosine kinases to control signalling pathways that underlie a broad spectrum of ...fundamental physiological processes. In this review, I describe recent breakthroughs in our understanding of the role of the PTPs in the regulation of signal transduction and the aetiology of human disease.
In October 2020, we were finally able to gather for a celebration of Eddy Fischer's 100th birthday. As with many other events, COVID had disrupted and restricted preparations for the gathering, which ...ultimately was held via ZOOM. Nevertheless, it was a wonderful opportunity to share a day with Eddy, an exceptional scientist and true renaissance man, and to appreciate his stellar contributions to science. Eddy Fischer, together with Ed Krebs, was responsible for the discovery of reversible protein phosphorylation, which launched the entire field of signal transduction. The importance of this seminal work is now being felt throughout the biotechnology industry with the development of drugs that target protein kinases, which have transformed the treatment of a wide array of cancers. I was privileged to have worked with Eddy both as a postdoc and a junior faculty member, during which time we laid the foundations for our current understanding of the protein tyrosine phosphatase (PTP) family of enzymes and their importance as critical regulators of signal transduction. This tribute to Eddy is based upon the talk I presented at the event, giving a personal perspective on Eddy's influence on my career, our early research efforts together in this area, and how the field has developed since then.
The protein-tyrosine phosphatase PTP1B is a negative regulator of insulin and leptin signaling and a highly validated therapeutic target for diabetes and obesity. Conventional approaches to drug ...development have produced potent and specific PTP1B inhibitors, but these inhibitors lack oral bioavailability, which limits their potential for drug development. Here, we report that DPM-1001, an analog of the specific PTP1B inhibitor trodusquemine (MSI-1436), is a potent, specific, and orally bioavailable inhibitor of PTP1B. DPM-1001 also chelates copper, which enhanced its potency as a PTP1B inhibitor. DPM-1001 displayed anti-diabetic properties that were associated with enhanced signaling through insulin and leptin receptors in animal models of diet-induced obesity. Therefore, DPM-1001 represents a proof of concept for a new approach to therapeutic intervention in diabetes and obesity. Although the PTPs have been considered undruggable, the findings of this study suggest that allosteric PTP inhibitors may help reinvigorate drug development efforts that focus on this important family of signal-transducing enzymes.
Although originally considered toxic, hydrogen sulfide (H(2)S) has been implicated in mediating various biological processes. Nevertheless, its cellular targets and mode of action are not well ...understood. Protein tyrosine phosphatases (PTPs), which regulate numerous signal transduction pathways, use an essential cysteine residue at the active site, which is characterized by a low pK(a) and is susceptible to reversible oxidation. Here, we report that PTP1B was reversibly inactivated by H(2)S, in vitro and in cells, through sulfhydration of the active-site cysteine residue. Unlike oxidized PTP1B, the sulfhydrated enzyme was preferentially reduced in vitro by thioredoxin, compared to glutathione or dithiothreitol. Sulfhydration of PTP1B in cells required the presence of cystathionine γ-lyase (CSE), a critical enzyme in H(2)S production, and resulted in inhibition of phosphatase activity. Suppression of CSE decreased H(2)S production and decreased the phosphorylation of tyrosine-619 in PERK protein kinase-like endoplasmic reticulum (ER) kinase, thus reducing its activation in response to ER stress. PERK, which phosphorylates the eukaryotic translational initiation factor 2, leading to attenuation of protein translation, was a direct substrate of PTP1B. In addition, CSE knockdown led to activation of the nonreceptor tyrosine kinase SRC, previously shown to be mediated by PTP1B. These effects of suppressing H(2)S production on the response to ER stress were abrogated by a small-molecule inhibitor of PTP1B. Together, these data define a signaling function for H(2)S in inhibiting PTP1B activity and thereby promoting PERK activity during the response to ER stress.
The architecture of the active site of members of the protein tyrosine phosphatase (PTP) superfamily renders these enzymes sensitive to reversible oxidation and inactivation. The importance of ...reversible oxidation of PTP superfamily members in controlling the signal output following an extracellular stimulus is discussed.
Protein tyrosine phosphatase 1B (PTP1B) plays important roles in downregulation of insulin and leptin signaling and is an established therapeutic target for diabetes and obesity. PTP1B is regulated ...by reactive oxygen species (ROS) produced in response to various stimuli, including insulin. The reversibly oxidized form of the enzyme (PTP1B-OX) is inactive and undergoes profound conformational changes at the active site. We generated conformation-sensor antibodies, in the form of single-chain variable fragments (scFvs), that stabilize PTP1B-OX and thereby inhibit its phosphatase function. Expression of conformation-sensor scFvs as intracellular antibodies (intrabodies) enhanced insulin-induced tyrosyl phosphorylation of the β subunit of the insulin receptor and its substrate IRS-1 and increased insulin-induced phosphorylation of PKB/AKT. Our data suggest that stabilization of the oxidized, inactive form of PTP1B with appropriate therapeutic molecules may offer a paradigm for phosphatase drug development.
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► Conformation-sensing antibodies recognize oxidized PTP1B (PTP1B-OX) ► The antibodies stabilize the oxidized, inactive phosphatase and inhibit reactivation ► PTP1B oxidation to the cyclic sulfenyl-amide species occurs in vivo and is reversible ► Intracellular PTP1B-OX antibodies enhance insulin signaling in an ROS-dependent manner
Selectively stabilizing the oxidized, inactive form of PTP1B enhances insulin signaling, suggesting a promising therapeutic target.
Copper is an essential nutrient whose redox properties make it both beneficial and toxic to the cell. Recent progress in studying transition metal signalling has forged new links between researchers ...of different disciplines that can help translate basic research in the chemistry and biology of copper into clinical therapies and diagnostics to exploit copper-dependent disease vulnerabilities. This concept is particularly relevant in cancer, as tumour growth and metastasis have a heightened requirement for this metal nutrient. Indeed, the traditional view of copper as solely an active site metabolic cofactor has been challenged by emerging evidence that copper is also a dynamic signalling metal and metalloallosteric regulator, such as for copper-dependent phosphodiesterase 3B (PDE3B) in lipolysis, mitogen-activated protein kinase kinase 1 (MEK1) and MEK2 in cell growth and proliferation and the kinases ULK1 and ULK2 in autophagy. In this Perspective, we summarize our current understanding of the connection between copper and cancer and explore how challenges in the field could be addressed by using the framework of cuproplasia, which is defined as regulated copper-dependent cell proliferation and is a representative example of a broad range of metalloplasias. Cuproplasia is linked to a diverse array of cellular processes, including mitochondrial respiration, antioxidant defence, redox signalling, kinase signalling, autophagy and protein quality control. Identifying and characterizing new modes of copper-dependent signalling offers translational opportunities that leverage disease vulnerabilities to this metal nutrient.
Although initially viewed as housekeeping enzymes, research over the last 15 years has revealed that the protein tyrosine phosphatases (PTPs) are critical regulators of tyrosine ...phosphorylation-dependent signaling events and may represent novel targets for therapeutic intervention in a variety of human diseases. In this review I will describe some of the key advances in the characterization of the structure, regulation and function of the prototypic PTP, PTP1B, and illustrate how our understanding of the properties of this enzyme has revealed principles that apply to the PTP family as a whole.
Oncogenic RAS (H-RASV12) induces premature senescence in primary cells by triggering production of reactive oxygen species (ROS), but the molecular role of ROS in senescence remains elusive. We ...investigated whether inhibition of protein tyrosine phosphatases by ROS contributed to H-RASV12-induced senescence. We identified protein tyrosine phosphatase 1B (PTP1B) as a major target of H-RASV12-induced ROS. Inactivation of PTP1B was necessary and sufficient to induce premature senescence in H-RASV12-expressing IMR90 fibroblasts. We identified phospho-Tyr 393 of argonaute 2 (AGO2) as a direct substrate of PTP1B. Phosphorylation of AGO2 at Tyr 393 inhibited loading with microRNAs (miRNAs) and thus miRNA-mediated gene silencing, which counteracted the function of H-RASV12-induced oncogenic miRNAs. Overall, our data illustrate that premature senescence in H-RASV12-transformed primary cells is a consequence of oxidative inactivation of PTP1B and inhibition of miRNA-mediated gene silencing.
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•PTP1B is reversibly oxidized by ROS in H-RASV12-transformed cells•Inactivation of PTP1B is required for H-RASV12-induced senescence•AGO2 phospho-Tyr 393 is a direct substrate of PTP1B•AGO2 phosphorylation at Tyr 393 inhibits its miRNA loading and gene silencing
Yang et al. demonstrate inactivation of protein tyrosine phosphatase PTP1B in response to oncogenic RAS-induced production of hydrogen peroxide. This led to enhanced tyrosine phosphorylation of argonaute 2, which impaired its ability to bind microRNA and its silencing of genes, such as p21, involved in onset of senescence.
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