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.

/pdf/h2s-induced-sulfhydration-of-the-phosphatase-ptp1b-and-its-z8q3izuzqa.pdf

H2S-Induced Sulfhydration of the Phosphatase PTP1B and Its Role in the Endoplasmic Reticulum Stress Response

PTP1B, a validated therapeutic target for diabetes and obesity, has a critical positive role in HER2 signaling in breast tumorigenesis. Efforts to develop therapeutic inhibitors of PTP1B have been frustrated by the chemical properties of the active site. We define a new mechanism of allosteric inhibition that targets the C-terminal, noncatalytic segment of PTP1B. We present what is to our knowledge the first ensemble structure of PTP1B containing this intrinsically disordered segment, within which we identified a binding site for the small-molecule inhibitor MSI-1436. We demonstrate binding to a second site close to the catalytic domain, with cooperative effects between the two sites locking PTP1B in an inactive state. MSI-1436 antagonized HER2 signaling, inhibited tumorigenesis in xenografts and abrogated metastasis in the NDL2 mouse model of breast cancer, validating inhibition of PTP1B as a therapeutic strategy in breast cancer. This new approach to inhibition of PTP1B emphasizes the potential of disordered segments of proteins as specific binding sites for therapeutic small molecules.

/pdf/targeting-the-disordered-c-terminus-of-ptp1b-with-an-32i4bnnvcq.pdf

Targeting the disordered C-terminus of PTP1B with an allosteric inhibitor

Obesity, a major risk factor for the development of diabetes mellitus, cardiovascular diseases and certain types of cancer, arises from a chronic positive energy balance that is often due to unlimited access to food and an increasingly sedentary lifestyle on the background of a genetic and epigenetic vulnerability. Our understanding of the humoral and neuronal systems that mediate the control of energy homeostasis has improved dramatically in the past few decades. However, our ability to develop effective strategies to slow the current epidemic of obesity has been hampered, largely owing to the limited knowledge of the mechanisms underlying resistance to the action of metabolic hormones such as leptin and ghrelin. The development of resistance to leptin and ghrelin, hormones that are crucial for the neuroendocrine control of energy homeostasis, is a hallmark of obesity. Intensive research over the past several years has yielded tremendous progress in our understanding of the cellular pathways that disrupt the action of leptin and ghrelin. In this Review, we discuss the molecular mechanisms underpinning resistance to leptin and ghrelin and how they can be exploited as targets for pharmacological management of obesity.

The cellular and molecular bases of leptin and ghrelin resistance in obesity.

Leptin, a hormone that is capable of effectively reducing food intake and body weight, was initially considered for use in the treatment of obesity. However, obese subjects have since been found to have high levels of circulating leptin and to be insensitive to the exogenous administration of leptin. The inability of leptin to exert its anorexigenic effects in obese individuals, and therefore, the lack of clinical utility of leptin in obesity, is defined as leptin resistance. This phenomenon has not yet been adequately characterized. Elucidation of the molecular mechanisms underlying leptin resistance is of vital importance for the application of leptin as an effective treatment for obesity. Leptin must cross the blood–brain barrier (BBB) to reach the hypothalamus and exert its anorexigenic functions. The mechanisms involved in leptin transportation across the blood–brain barrier continue to be unclear, thereby preventing the clinical application of leptin in the treatment of obesity. In recent years, new strategies have been developed to recover the response to leptin in obesity. We have summarized these strategies in this review.

https://www.mdpi.com/2072-6643/11/11/2704/pdf

Leptin, Obesity, and Leptin Resistance: Where Are We 25 Years Later?

Several 'classical' protein tyrosine phosphatases are attractive therapeutic targets, including PTP1B for obesity and Type II diabetes; SHP2 for cancer and Lyp for rheumatoid arthritis. Progress has been made in identifying a broad range of chemically distinct inhibitors; however, developing selective and cell-permeable clinically useful compounds has proved challenging. Here the ongoing challenges and recent significant advances in the field are reviewed. Key novel compounds are highlighted and a perspective on the future of phosphatase inhibitor development is presented.

https://www.future-science.com/doi/pdf/10.4155/fmc.10.241

Protein tyrosine phosphatases as drug targets: strategies and challenges of inhibitor development

Trodusquemine (MSI-1436) causes rapid and reversible weight loss in genetic models of obesity. To better predict the potential effects of trodusquemine in the clinic, we investigated the effects of trodusquemine treatment in a murine model of diet-induced obesity (DIO). Trodusquemine suppressed appetite, reduced body weight (BW) in a fat-specific manner, and improved plasma insulin and leptin levels in mice. Screening assays revealed that trodusquemine selectively inhibited protein-tyrosine phosphatase 1B (PTP1B), a key enzyme regulating insulin and leptin signaling. Trodusquemine significantly enhanced insulin-stimulated tyrosine phosphorylation of insulin receptor (IR) β and STAT3, direct targets of PTP1B, in HepG2 cells in vitro and/or hypothalamic tissue in vivo. These data establish trodusquemine as an effective central and peripheral PTP1B inhibitor with the potential to elicit noncachectic fat-specific weight loss and improve insulin and leptin levels.

https://onlinelibrary.wiley.com/doi/pdf/10.1038/oby.2009.444

Inhibition of PTP1B by trodusquemine (MSI-1436) causes fat-specific weight loss in diet-induced obese mice.

This application is directed to the use of steroid compounds for the selective inhibition of the enzyme PTP1B in a mammal for the treatment of diabetes.

A method for treating diabetes

This application is directed to the use of aminosteroid compounds for the selective inhibition of the enzyme PTP1B in a mammal for the treatment of diabetes.

Aminosteroids for the treatment of a ptp1b associated disease

Method for treating diabetes

This invention relates to the use of trodusquemine to treat a rapamycin-induced diabetic- like syndrome in a mammal. Data is presented demonstrating that trodusquemine can reverse short term and long term glucose intolerance and can reverse hyperglycemia in a diet induced obese animal.

Inez Ruiz-White

Papers

Inhibition of PTP1B by trodusquemine (MSI-1436) causes fat-specific weight loss in diet-induced obese mice.

A method for treating diabetes

Aminosteroids for the treatment of a ptp1b associated disease

Method for treating diabetes

A method for treating rapamycin induced diabetes-like syndrome using trodusquemine