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The activation of PP5 is essential for a variety of cellular processes, as it participates in a variety of biological pathways by dephosphorylating substrates. However, activation of PP5 by small molecules has been a challenge due to its native "self-inhibition" mechanism, which is controlled by the N-terminal TPR domain and the C-terminal αJ helix. Here, we reported the discovery of DDO-3733 , a well-identified TPR-independent PP5 allosteric activator, which facilitates the dephosphorylation process of downstream substrates. Considering the negative regulatory effect of PP5 on heat shock transcription factor HSF1, pharmacologic activation of PP5 by DDO-3733 was found to reduce the HSP90 inhibitor-induced heat shock response. These results provide a chemical tool to advance the exploration of PP5 as a potential therapeutic target and highlight the value of pharmacological activation of PP5 to reduce heat shock toxicity of HSP90 inhibitors.

Working in tandem with kinases via a dynamic interplay of phosphorylation and dephosphorylation of proteins, phosphatases regulate many cellular processes and thus represent compelling therapeutic targets. Here we leverage ultraviolet photodissociation to shed light on the binding characteristics of two covalent phosphatase inhibitors, T65 and rabeprazole, and their respective interactions with the human small C-terminal domain phosphatase 1 (SCP1) and its single-point mutant C181A, in which a nonreactive alanine replaces one key reactive cysteine. Top-down MS/MS analysis is used to localize the binding of T65 and rabeprazole on the two proteins and estimate the relative reactivities of each cysteine residue.

Objective: Phlpp1 inhibition is a potential therapeutic strategy for cartilage regeneration and prevention of post-traumatic osteoarthritis (PTOA). To understand how Phlpp1 loss affects cartilage structure, cartilage elastic modulus was measured with atomic force microscopy (AFM) in male and female mice after injury., Methods: Osteoarthritis was induced in male and female Wildtype (WT) and Phlpp1 -/- mice by destabilization of the medial meniscus (DMM). At various timepoints post-injury, activity was measured, and knee joints examined with AFM and histology. In another cohort of WT mice, the PHLPP inhibitor NSC117079 was intra-articularly injected 4 weeks after injury., Results: Male WT mice showed decreased activity and histological signs of cartilage damage at 12 but not 6-weeks post-DMM. Female mice showed a less severe response to DMM by comparison, with no histological changes seen at any time point. In both sexes the elastic modulus of medial condylar cartilage was decreased in WT mice but not Phlpp1 -/- mice after DMM as measured by AFM. By 6-weeks, cartilage modulus had decreased from 2 MPa to 1 MPa in WT mice. Phlpp1 -/- mice showed no change in modulus at 6-weeks and only a 25% decrease at 12-weeks. The PHLPP inhibitor NSC117079 protected cartilage structure and prevented signs of OA 6-weeks post-injury., Conclusions: AFM is a sensitive method for detecting early changes in articular cartilage post-injury. Phlpp1 suppression, either through genetic deletion or pharmacological inhibition, protects cartilage degradation in a model of PTOA, validating Phlpp1 as a therapeutic target for PTOA., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2024 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)

There exists a huge number of patients suffering from chronic liver disease worldwide. As a disease with high incidence and mortality worldwide, strengthening the research on the pathogenesis of chronic liver disease and the development of novel drugs is an important issue related to the health of all human beings. Phosphorylation modification of proteins plays a crucial role in cellular signal transduction, and phosphatases are involved in the development of liver diseases. Therefore, this article summarized the important role of protein phosphatases in chronic liver disease with the aim of facilitating the development of drugs targeting protein phosphatases for the treatment of chronic liver disease., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Okadaic acid (OA) is an important marine lipophilic phycotoxin responsible for diarrhetic shellfish poisoning (DSP). This toxin inhibits protein phosphatases (PPs) like PP2A and PP1, though, this action does not explain OA-induced toxicity and symptoms. Intestinal epithelia comprise the defence barrier against external agents where transport of fluid and electrolytes from and to the lumen is a tightly regulated process. In some intoxications this balance becomes dysregulated appearing diarrhoea. Therefore, we evaluated diarrhoea in orally OA-treated mice as well as in mice pre-treated with several doses of cyproheptadine (CPH) and then treated with OA at different times. We assessed stools electrolytes and ultrastructural alteration of the intestine, particularly evaluating tight and adherens junctions. We detected increased chloride and sodium faecal concentrations in the OA-exposed group, suggesting a secretory diarrhoea. Pre-treatment with CPH maintains chloride concentration in values similar to control mice. Intestinal cytomorphological alterations were observed for OA mice, whereas CPH pre-treatment attenuated OA-induced damage in proximal colon and jejunum at 2 h. Conversely, tight junctions' distance was only affected by OA in jejunum at the moment diarrhoea occurred. In this study we found cellular mechanisms by which OA induced diarrhoea revealing the complex toxicity of this compound., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Phosphatase PPM1F is a regulator of cell adhesion by fine-tuning integrin activity and actin cytoskeleton structures. Elevated expression of this enzyme in human tumors is associated with high invasiveness, enhanced metastasis, and poor prognosis. Thus, PPM1F is a target for pharmacological intervention, yet inhibitors of this enzyme are lacking. Here, we use high-throughput screening to identify Lockdown, a reversible and non-competitive PPM1F inhibitor. Lockdown is selective for PPM1F, because this compound does not inhibit other protein phosphatases in vitro and does not induce additional phenotypes in PPM1F knockout cells. Importantly, Lockdown-treated glioblastoma cells fully re-capitulate the phenotype of PPM1F-deficient cells as assessed by increased phosphorylation of PPM1F substrates and corruption of integrin-dependent cellular processes. Ester modification yields Lockdown Pro with increased membrane permeability and prodrug-like properties. Lockdown Pro suppresses tissue invasion by PPM1F-overexpressing human cancer cells, validating PPM1F as a therapeutic target and providing an access point to control tumor cell dissemination., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The repressor element-1 silencing transcription factor (REST) represses neuronal gene expression, whose dysregulation is implicated in brain tumors and neurological diseases. A high level of REST protein drives the tumor growth in some glioblastoma cells. While transcription factors like REST are challenging targets for small-molecule inhibitors, the inactivation of a regulatory protein, small CTD phosphatase 1 (SCP1), promotes REST degradation and reduces transcriptional activity. This study rationally designed a series of α,β-unsaturated sulfones to serve as potent and selective covalent inhibitors against SCP1. The compounds inactivate SCP1 via covalent modification of Cys181 located at the active site entrance. Cellular studies showed that the inhibitors inactivate SCP1 in a time- and dose-dependent manner with an EC 50 ∼1.5 μM, reducing REST protein levels and activating specific REST-suppressed genes. These compounds represent a promising line of small-molecule inhibitors as a novel lead for glioblastoma whose growth is driven by REST transcription activity.

Breast cancer is the leading cause of cancer-related death in women worldwide, and despite multiple chemotherapeutic approaches, effective treatment strategies for advanced metastatic breast cancer are still lacking. Metabolic reprogramming is essential for tumor cell growth and propagation, and most cancers, including breast cancer, are accompanied by abnormalities in energy metabolism. Here, we confirmed that sodium cantharidate inhibited cell viability using the Cell Counting Kit-8, clonogenic assay, and Transwell assay. The cell cycle and apoptosis assays indicated that sodium cantharidate induced apoptosis and cell cycle arrest in breast cancer cells. Additionally, proteomic assays, western blots, and metabolic assays revealed that sodium cantharidate converted the metabolic phenotype of breast cancer cells from glycolysis to oxidative phosphorylation. Furthermore, bioinformatics analysis identified possible roles for p53 with respect to the effects of sodium cantharidate on breast cancer cells. Western blot, docking, and phosphatase assays revealed that the regulation of p53 activity by sodium cantharidate was related to its inhibition of protein phosphatase 5 activity. Moreover, sodium cantharidate significantly inhibited tumor growth in tumor-bearing nude mice. In summary, our study provides evidence for the use of sodium cantharidate as an effective and new therapeutic candidate for the treatment of human breast cancer in clinical trials., (Copyright © 2021. Published by Elsevier Inc.)