Targeting undruggable phosphatase overcomes trastuzumab resistance by inhibiting multi-oncogenic kinases

AIMS

Resistance to targeted therapy is one of the critical obstacles in cancer management. Resistance to trastuzumab frequently develops in the treatment for HER2+ cancers. The role of protein tyrosine phosphatases (PTPs) in trastuzumab resistance is not well understood. In this study, we aim to identify pivotal PTPs affecting trastuzumab resistance and devise a novel counteracting strategy.

METHODS

Four public datasets were used to screen PTP candidates in relation to trastuzumab responsiveness in HER2+ breast cancer. Tyrosine kinase (TK) arrays were used to identify kinases that linked to protein tyrosine phosphate receptor type O (PTPRO)-enhanced trastuzumab sensitivity. The efficacy of small activating RNA (saRNA) in trastuzumab-conjugated silica nanoparticles was tested for PTPRO upregulation and resistance mitigation in cell models, a transgenic mouse model, and human cancer cell line-derived xenograft models.

RESULTS

PTPRO was identified as the key PTP which influences trastuzumab responsiveness and patient survival. PTPRO de-phosphorated several TKs, including the previously overlooked substrate ERBB3, thereby inhibiting multiple oncogenic pathways associated with drug resistance. Notably, PTPRO, previously deemed "undruggable," was effectively upregulated by saRNA-loaded nanoparticles. The upregulated PTPRO simultaneously inhibited ERBB3, ERBB2, and downstream SRC signaling pathways, thereby counteracting trastuzumab resistance.

CONCLUSIONS

Antibody-conjugated saRNA represents an innovative approach for targeting "undruggable" PTPs.

In silico identification of putative druggable pockets in PRL3, a significant oncology target

Protein tyrosine phosphatases (PTP) have emerged as targets in diseases characterized by aberrant phosphorylations such as cancers. The activity of the phosphatase of regenerating liver 3, PRL3, has been linked to several oncogenic and metastatic pathways, particularly in breast, ovarian, colorectal, and blood cancers. Development of small molecules that directly target PRL3, however, has been challenging. This is partly due to the lack of structural information on how PRL3 interacts with its inhibitors. Here, computational methods are used to bridge this gap by evaluating the druggability of PRL3. In particular, web-based pocket prediction tools, DoGSite3 and FTMap, were used to identify binding pockets using structures of PRL3 currently available in the Protein Data Bank. Druggability assessment by molecular dynamics simulations with probes was also performed to validate these results and to predict the strength of binding in the identified pockets. While several druggable pockets were identified, those in the closed conformation show more promise given their volume and depth. These two pockets flank the active site loops and roughly correspond to pockets predicted by molecular docking in previous papers. Notably, druggability simulations predict the possibility of low nanomolar affinity inhibitors in these sites implying the potential to identify highly potent small molecule inhibitors for PRL3. Putative pockets identified here can be leveraged for high-throughput virtual screening to further accelerate the drug discovery against PRL3 and development of PRL3-directed therapeutics.

Impact of Protein Phosphatase Expressions on the Prognosis of Hepatocellular Carcinoma Patients

The study was conducted to unveil the significance of protein phosphatases in the prognosis of hepatocellular carcinoma (HCC) patients and its related molecular biological attributes as well as to discover novel potential biomarkers for therapeutic significance and diagnostic purposes that may benefit clinical practice. Analyzing a data set from 159 HCC patients using high-throughput phosphoproteomics, we examined the dysregulated expression of protein phosphatases. Employing bioinformatic and pathway analyses, we explored differentially expressed genes linked to protein phosphatases. A protein-protein interaction network was constructed using the search tool for the retrieval of interacting genes/proteins database. We quantified a total of 11,547 phosphorylation sites associated with 4043 phosphoproteins from HCC patients. Within this data set, we identified 105 identified phosphorylation sites associated with protein phosphatases; 28 genes were upregulated and 3 were downregulated in HCC. Enriched pathways using Gene Set Enrichment Analysis encompassed oocyte meiosis, proteoglycans in cancer, the oxytocin signaling pathway, the cGMP-PKG signaling pathway, the vascular smooth muscle, and the cAMP signaling pathway. The Kyoto encyclopedia of genes and genomes (KEGG) analysis highlighted pathways like mitogen-activated protein kinase, AMPK, and PI3K-Akt, indicating potential involvement in HCC progression. Notably, the PPI network identified hub genes, emphasizing their interconnections and potential roles in HCC. In our study, we found significantly upregulated levels of CDC25C, PPP1R13L, and PPP1CA, which emerge as promising avenues. This significant expression could serve as potent diagnostic and prognostic markers to enhance the effectiveness of HCC cancer treatment, offering efficiency and accuracy in patient assessment. The findings regarding protein phosphatases reveal their elevated expression in HCC, correlating with unfavorable prognosis. Moreover, the outcomes of gene ontology and KEGG pathway analyses suggest that protein phosphatases may influence liver cancer by engaging diverse targets and pathways, ultimately fostering the progression of HCC. These results underscore the substantial potential of protein phosphatases as key contributors to HCC's development and advancement. This insight holds promise for identifying therapeutic targets and charting research avenues to enhance the comprehension of the intricate molecular mechanisms underpinning HCC.

Chronological Analysis of First-in-Class Drugs Approved from 2011 to 2022: Their Technological Trend and Origin

The discovery and development of first-in-class (FIC) drugs are becoming increasingly important due to increasing reimbursement pressure and personalized medication. To investigate the technological trends and origin of FIC drugs, the FIC drugs approved in the U.S. from January 2011 to December 2022 were analyzed. The analysis shows that previous major target families, viz. enzymes, G-protein coupled receptors, transporters, and transcription factors, are no longer considered major in recent years. Instead, the shares of secreted proteins/peptides and mRNAs have continuously increased from 2011-2014 to 2019-2022, suggesting that the target family of FIC drugs has shifted to molecules previously considered challenging as drug targets. Small molecules were predominant in 2011-2014, followed by a large increase in antibody medicines in 2015-2018 and further diversification of antibody medicine modalities in 2019-2022. Nucleic acid medicine has also continuously increased its share, suggesting that diversifying modalities supports the creation of FIC drugs toward challenging target molecules. Over half of FIC drugs were created by small and medium enterprises (SMEs), especially young companies established in the 1990s and 2000s. All SMEs that produced more than one FIC drug approved in 2019-2022 have the strong technological capability in a specific modality. Investment in modality technologies and facilitating mechanisms to translate academic modality technologies to start-ups might be important for enhancing FIC drug development.

Discovery of Novel Small-Molecule Scaffolds for the Inhibition and Activation of WIP1 Phosphatase from a RapidFire Mass Spectrometry High-Throughput Screen

Wild-type P53-induced phosphatase 1 (WIP1), also known as PPM1D or PP2Cδ, is a serine/threonine protein phosphatase induced by P53 after genotoxic stress. WIP1 inhibition has been proposed as a therapeutic strategy for P53 wild-type cancers in which it is overexpressed, but this approach would be ineffective in P53-negative cancers. Furthermore, there are several cancers with mutated P53 where WIP1 acts as a tumor suppressor. Therefore, activating WIP1 phosphatase might also be a therapeutic strategy, depending on the P53 status. To date, no specific, potent WIP1 inhibitors with appropriate pharmacokinetic properties have been reported, nor have WIP1-specific activators. Here, we report the discovery of new WIP1 modulators from a high-throughput screen (HTS) using previously described orthogonal biochemical assays suitable for identifying both inhibitors and activators. The primary HTS was performed against a library of 102 277 compounds at a single concentration using a RapidFire mass spectrometry assay. Hits were further evaluated over a range of 11 concentrations with both the RapidFire MS assay and an orthogonal fluorescence-based assay. Further biophysical, biochemical, and cell-based studies of confirmed hits revealed a WIP1 activator and two inhibitors, one competitive and one uncompetitive. These new scaffolds are prime candidates for optimization which might enable inhibitors with improved pharmacokinetics and a first-in-class WIP1 activator.

Phosphatase inhibition by sodium orthovanadate displays anti-inflammatory action by suppressing AKT-IKKβ signaling in RAW264.7 cells

Sodium orthovanadate (Na3VO4) is an inhibitor of phosphatases that acts as a phosphate analog and is being developed as an anti-diabetes drug. Phosphatases play important roles in inflammatory signal pathways by modulating the removal of phosphate moieties of key signaling proteins. However, the role of protein phosphatases on the inflammatory response has not been fully established. In this study, we investigated how phosphatases can control the inflammatory response using Na3VO4 in LPS-stimulated RAW264.7 cells and explored the molecular mechanisms by NO assay, mRNA analysis, immunoblotting analysis, kinase assay, luciferase reporter gene assay, and mutation strategy. Na3VO4 decreased the release of nitric oxide (NO) and suppressed the expression of pro-inflammatory genes at the transcriptional level, without cytotoxicity. The translocation of nuclear factor (NF)-κB subunits into the nucleus and the level of p-IκBα were reduced by Na3VO4, as was IKKβ activity. Na3VO4 inhibited NF-κB-Luc activity under AKT1/2 and IKKβ overexpression. However, the inhibitory effect of Na3VO4 against NF-κB-Luc was not observed in the group overexpressing both AKT2 and IKKβ-M10, a mutant in which the 10 serine residues in the autophosphorylated region of the C-terminal were replaced with alanine. Na3VO4 directly decreased the activity of protein phosphatase 1α (PP1α) and protein phosphatase 2 A (PP2A) by 95%. Phosphatase inhibition by Na3VO4 also selectively suppressed AKT-IKKβ signaling by directly blocking the phosphatase activity of PP1 and PP2A, consequently down-regulating NF-κB and inflammatory gene expression. Therefore, these results suggest that vanadium compounds including Na3VO4 can be developed as anti-inflammatory drugs.

Mapping the binding sites of challenging drug targets

An increasing number of medically important proteins are challenging drug targets because their binding sites are too shallow or too polar, are cryptic and thus not detectable without a bound ligand or located in a protein-protein interface. While such proteins may not bind druglike small molecules with sufficiently high affinity, they are frequently druggable using novel therapeutic modalities. The need for such modalities can be determined by experimental or computational fragment based methods. Computational mapping by mixed solvent molecular dynamics simulations or the FTMap server can be used to determine binding hot spots. The strength and location of the hot spots provide very useful information for selecting potentially successful approaches to drug discovery.

CDC25B Inhibition by menadione: a potential new therapeutical approach

Gastric cancer (GC) is the fifth most common type of tumor and the third leading cause of cancer death worldwide. The evolution of gastric carcinogenesis is still poorly understood and, for this reason, preclinical research protocols were established that included the development of gastric cancer cell lines and the establishment of models of gastric carcinogenesis in non-human primate Sapajus apella. A comprehensive literature search was performed in relevant databases such as PubMed, ResearchGate and Google Scholar to identify studies related to the topic. After an in-depth study of these reports, significant data/data were collected and compiled under appropriate headings. The main result of the studies carried out by the group on GC is the demonstration of the MYC gene overexpression as a common phenomenon in stomach carcinogenesis. Furthermore, we revealed that reducing the expression of the CDC25B gene, regulated by the MYC protein, is a therapeutic strategy against stomach tumors. This review article reveals preclinical evidence that treatment with menadione in experimental models of gastric tumorigenesis, in vivo and in vitro, inhibits the action of the phosphatase CDC25B and, consequently, prevents cell proliferation, invasion and migration.

Antibacterial Profile of a Microbicidal Agent Targeting Tyrosine Phosphatases and Redox Thiols, Novel Drug Targets

The activity profile of a protein tyrosine phosphatase (PTP) inhibitor and redox thiol oxidant, nitropropenyl benzodioxole (NPBD), was investigated across a broad range of bacterial species. In vitro assays assessed inhibitory and lethal activity patterns, the induction of drug variants on long term exposure, the inhibitory interactions of NPBD with antibiotics, and the effect of plasma proteins and redox thiols on activity. A literature review indicates the complexity of PTP and redox signaling and suggests likely metabolic targets. NPBD was broadly bactericidal to pathogens of the skin, respiratory, urogenital and intestinal tracts. It was effective against antibiotic resistant strains and slowly replicating and dormant cells. NPBD did not induce resistant or drug-tolerant phenotypes and showed low cross reactivity with antibiotics in synergy assays. Binding to plasma proteins indicated lowered in-vitro bioavailability and reduction of bactericidal activity in the presence of thiols confirmed the contribution of thiol oxidation and oxidative stress to lethality. This report presents a broad evaluation of the antibacterial effect of PTP inhibition and redox thiol oxidation, illustrates the functional diversity of bacterial PTPs and redox thiols, and supports their consideration as novel targets for antimicrobial drug development. NPBD is a dual mechanism agent with an activity profile which supports consideration of tyrosine phosphatases and bacterial antioxidant systems as promising targets for drug development.

Synthesis and evaluation of bifunctional PTP4A3 phosphatase inhibitors activating the ER stress pathway

We developed JMS-053, a potent inhibitor of the dual specificity phosphatase PTP4A3 that is potentially suitable for cancer therapy. Due to the emerging role of the unfolded protein response (UPR) in cancer pathology, we sought to identify derivatives that combine PTP4A3 inhibition with induction of endoplasmatic reticulum (ER) stress, with the goal to generate more potent anticancer agents. We have now generated bifunctional analogs that link the JMS-053 pharmacophore to an adamantyl moiety and act in concert with the phosphatase inhibitor to induce ER stress and cell death. The most potent compound in this series, 7a, demonstrated a ca. 5-fold increase in cytotoxicity in a breast cancer cell line and strong activation of UPR and ER stress response genes in spite of a ca. 13-fold decrease in PTP4A3 inhibition. These results demonstrate that the combination of phosphatase inhibition with UPR/ER-stress upregulation potentiates efficacy.

Phosphatases in toll-like receptors signaling: the unfairly-forgotten

Over the past 2 decades, pattern recognition receptors (PRRs) have been shown to be on the front line of many illnesses such as autoimmune, inflammatory, and neurodegenerative diseases as well as allergies and cancer. Among PRRs, toll-like receptors (TLRs) are the most studied family. Dissecting TLRs signaling turned out to be advantageous to elaborate efficient treatments to cure autoimmune and chronic inflammatory disorders. However, a broad understanding of TLR effectors is required to propose a better range of cures. In addition to kinases and E3 ubiquitin ligases, phosphatases emerge as important regulators of TLRs signaling mediated by NF-κB, type I interferons (IFN I) and Mitogen-Activated Protein Kinases signaling pathways. Here, we review recent knowledge on TLRs signaling modulation by different classes and subclasses of phosphatases. Thus, it becomes more and more evident that phosphatases could represent novel therapeutic targets to control pathogenic TLRs signaling. Video Abstract.

Emerging chemical scaffolds with potential SHP2 phosphatase inhibitory capabilities - A comprehensive review

The drug discovery panorama is cluttered with promising therapeutic targets that have been deserted because of inadequate authentication and screening failures. Molecular targets formerly tagged as "undruggable" are nowadays being more cautiously cross-examined, and whilst they stay intriguing, numerous targets are emerging more accessible. Protein tyrosine phosphatases (PTPs) excellently exemplifies a class of molecular targets that have transpired as druggable, with several small molecules and antibodies recently turned available for further development. In this respect, SHP2, a PTP, has emerged as one of the potential targets in the current pharmacological research, particularly for cancer, due to its critical role in various signalling pathways. Recently, few molecules with excellent potency have entered clinical trials, but none could reach the clinic. Consequently, search for novel, non-toxic, and specific SHP2 inhibitors are on purview. In this review, general aspects of SHP2 including its structure and mechanistic role in carcinogenesis have been presented. It also sheds light on the development of novel molecular architectures belonging to diverse chemical classes that have been proposed as SHP2-specific inhibitors along with their structure-activity relationships (SARs), stemming from chemical, mechanism-based and computer-aided studies reported since January 2015 to July 2020 (excluding patents), focusing on their potency and selectivity. The encyclopedic facts and discussions presented herein will hopefully facilitate researchers to design new ligands with better efficacy and selectivity against SHP2.

Modeling the Alkaline Hydrolysis of Diaryl Sulfate Diesters: A Mechanistic Study

Phosphate and sulfate esters have important roles in regulating cellular processes. However, while there has been substantial experimental and computational investigation of the mechanisms and the transition states involved in phosphate ester hydrolysis, there is far less work on sulfate ester hydrolysis. Here, we report a detailed computational study of the alkaline hydrolysis of diaryl sulfate diesters, using different DFT functionals as well as mixed implicit/explicit solvation with varying numbers of explicit water molecules. We consider the impact of the computational model on computed linear free-energy relationships (LFER) and the nature of the transition states (TS) involved. We obtain good qualitative agreement with experimental LFER data when using a pure implicit solvent model and excellent agreement with experimental kinetic isotope effects for all models used. Our calculations suggest that sulfate diester hydrolysis proceeds through loose transition states, with minimal bond formation to the nucleophile and bond cleavage to the leaving group already initiated. Comparison to prior work indicates that these TS are similar in nature to those for the alkaline hydrolysis of neutral arylsulfonate monoesters or charged phosphate diesters and fluorophosphates. Obtaining more detailed insights into the transition states involved assists in understanding the selectivity of enzymes that hydrolyze these reactions.

Controlling Phosphate Removal with Light: The Development of Optochemical Tools to Probe Protein Phosphatase Function

Protein phosphatases play an essential role in cell signaling; however, they remain understudied compared with protein kinases, in part due to a lack of appropriate tools. In order to provide conditional control over phosphatase function, we developed two different approaches for rendering MKP3 (a dual-specific phosphatase, also termed DUSP6) activatable by light. Specifically, we expressed the protein with strategically placed light-removable protecting groups in cells with an expanded genetic code. This allowed for the acute perturbation of the Ras/MAPK signaling pathway upon photoactivation in live cells. In doing so, we confirmed that MKP3 does not act as a thresholding gate for growth factor stimulation of the extracellular signal-regulated kinase (ESRK) pathway.

Caenorhabditis elegans phosphatase complexes in UniProtKB and Complex Portal

Phosphatases play an essential role in the regulation of protein phosphorylation. Less abundant than kinases, many phosphatases are components of one or more macromolecular complexes with different substrate specificities and specific functionalities. The expert scientific curation of phosphatase complexes for the UniProt and Complex Portal databases supports the whole scientific community by collating and organising small- and large-scale experimental data from the scientific literature into context-specific central resources, where the data can be freely accessed and used to further academic and translational research. In this review, we discuss how the diverse biological functions of phosphatase complexes are presented in UniProt and the Complex Portal, and how understanding the biological significance of phosphatase complexes in Caenorhabditis elegans offers insight into the mechanisms of substrate diversity in a variety of cellular and molecular processes.

Synthesis and PTP Inhibitory Activity of Illudalic Acid and Its Methyl Ether, with Insights into Selectivity for LAR PTP over Other Tyrosine Phosphatases under Physiologically Relevant Conditions

The protein tyrosine phosphatase (PTP) family of enzymes includes many attractive therapeutic targets, such as those in the leukocyte common antigen-related (LAR) subfamily of receptor PTPs. Synthesis and PTP inhibitory activity of illudalic acid and its methyl ether are described, with a focus on selective inhibition of LAR PTP relative to a small collection of other representative PTPs. The synthesis comprises 16 steps and provides illudalic acid in up to 12% overall yield from neopentylene-fused benzoate 1 (20 steps from commercial materials). Illudalic acid dose-dependently (measured IC₅₀ = 2.1 ± 0.2 μM) and time-dependently inhibits LAR consistent with previous reports of covalent binding. The kinetics of LAR inhibition by illudalic acid are consistent with a two-step mechanism in which the inhibitor and enzyme first interact noncovalently (K_I = 130 ± 50 μM), followed by covalent ligation at a rate k_inact = 1.3 ± 0.4 min^-1. The k_inact/K_I ratio of 10⁴ corresponds to a t^∞_1/2 of 0.5 min, as discussed herein. The phenol methyl ether of illudalic acid was found to be less potent in our dose-response assays (measured IC₅₀ = 55 ± 6 μM) but more selective for LAR, with a weaker initial noncovalent interaction and faster covalent ligation of LAR as compared to illudalic acid itself. A truncated analogue of illudalic acid that lacks the neopentylene ring fusion was found to be devoid of significant activity under our assay conditions, in contrast to previous reports. These observations collectively help inform further development of illudalic acid analogues as potent and selective inhibitors of the LAR subfamily of tyrosine phosphatases.

Physiologically relevant orthogonal assays for the discovery of small-molecule modulators of WIP1 phosphatase in high-throughput screens

WT P53-Induced Phosphatase 1 (WIP1) is a member of the magnesium-dependent serine/threonine protein phosphatase (PPM) family and is induced by P53 in response to DNA damage. In several human cancers, the WIP1 protein is overexpressed, which is generally associated with a worse prognosis. Although WIP1 is an attractive therapeutic target, no potent, selective, and bioactive small-molecule modulator with favorable pharmacokinetics has been reported. Phosphatase enzymes are among the most challenging targets for small molecules because of the difficulty of achieving both modulator selectivity and bioavailability. Another major obstacle has been the availability of robust and physiologically relevant phosphatase assays that are suitable for high-throughput screening. Here, we describe orthogonal biochemical WIP1 activity assays that utilize phosphopeptides from native WIP1 substrates. We optimized an MS assay to quantify the enzymatically dephosphorylated peptide reaction product in a 384-well format. Additionally, a red-shifted fluorescence assay was optimized in a 1,536-well format to enable real-time WIP1 activity measurements through the detection of the orthogonal reaction product, P_i. We validated these two optimized assays by quantitative high-throughput screening against the National Center for Advancing Translational Sciences (NCATS) Pharmaceutical Collection and used secondary assays to confirm and evaluate inhibitors identified in the primary screen. Five inhibitors were further tested with an orthogonal WIP1 activity assay and surface plasmon resonance binding studies. Our results validate the application of miniaturized physiologically relevant and orthogonal WIP1 activity assays to discover small-molecule modulators from high-throughput screens.

Structural and Functional Analyses of an Allosteric EYA2 Phosphatase Inhibitor That Has On-Target Effects in Human Lung Cancer Cells

EYA proteins (EYA1-4) are critical developmental transcriptional cofactors that contain an EYA domain (ED) harboring Tyr phosphatase activity. EYA proteins are largely downregulated after embryogenesis but are reexpressed in cancers, and their Tyr phosphatase activity plays an important role in the DNA damage response and tumor progression. We previously identified a class of small-molecule allosteric inhibitors that specifically inhibit the Tyr phosphatase activity of EYA2. Herein, we determined the crystal structure of the EYA2 ED in complex with NCGC00249987 (a representative compound in this class), revealing that it binds to an induced pocket distant from the active site. NCGC00249987 binding leads to a conformational change of the active site that is unfavorable for Mg²⁺ binding, thereby inhibiting EYA2's Tyr phosphatase activity. We demonstrate, using genetic mutations, that migration, invadopodia formation, and invasion of lung adenocarcinoma cells are dependent on EYA2 Tyr phosphatase activity, whereas growth and survival are not. Further, we demonstrate that NCGC00249987 specifically targets migration, invadopodia formation, and invasion of lung cancer cells, but that it does not inhibit cell growth or survival. The compound has no effect on lung cancer cells carrying an EYA2 F290Y mutant that abolishes compound binding, indicating that NCGC00249987 is on target in lung cancer cells. These data suggest that the NCGC00249987 allosteric inhibitor can be used as a chemical probe to study the function of the EYA2 Tyr phosphatase activity in cells and may have the potential to be developed into an antimetastatic agent for cancers reliant on EYA2's Tyr phosphatase activity.

Rapid approach to complex boronic acids

The compatibility of free boronic acid building blocks in multicomponent reactions to readily create large libraries of diverse and complex small molecules was investigated. Traditionally, boronic acid synthesis is sequential, synthetically demanding, and time-consuming, which leads to high target synthesis times and low coverage of the boronic acid chemical space. We have performed the synthesis of large libraries of boronic acid derivatives based on multiple chemistries and building blocks using acoustic dispensing technology. The synthesis was performed on a nanomole scale with high synthesis success rates. The discovery of a protease inhibitor underscores the usefulness of the approach. Our acoustic dispensing-enabled chemistry paves the way to highly accelerated synthesis and miniaturized reaction scouting, allowing access to unprecedented boronic acid libraries.

PP2A: A Promising Biomarker and Therapeutic Target in Endometrial Cancer

Over the last decade, the use of targeted therapies has immensely increased in the treatment of cancer. However, treatment for endometrial carcinomas (ECs) has lagged behind, although potential molecular markers have been identified. This is particularly problematic for the type II ECs, since these aggressive tumors are usually not responsive toward the current standard therapies. Therefore, type II ECs are responsible for most EC-related deaths, indicating the need for new treatment options. Interestingly, molecular analyses of type II ECs have uncovered frequent genetic alterations (up to 40%) in PPP2R1A, encoding the Aα subunit of the tumor suppressive heterotrimeric protein phosphatase type 2A (PP2A). PPP2R1A mutations were also reported in type I ECs and other common gynecologic cancers, albeit at much lower frequencies (0-7%). Nevertheless, PP2A inactivation in the latter cancer types is common via other mechanisms, in particular by increased expression of Cancerous Inhibitor of PP2A (CIP2A) and PP2A Methylesterase-1 (PME-1) proteins. In this review, we discuss the therapeutic potential of direct and indirect PP2A targeting compounds, possibly in combination with other anti-cancer drugs, in EC. Furthermore, we investigate the potential of the PP2A status as a predictive and/or prognostic marker for type I and II ECs.

Functions and therapeutic potential of protein phosphatase 1: Insights from mouse genetics

Protein phosphatase 1 (PP1) catalyzes more than half of all phosphoserine/threonine dephosphorylation reactions in mammalian cells. In vivo PP1 does not exist as a free catalytic subunit but is always associated with at least one regulatory PP1-interacting protein (PIP) to generate a large set of distinct holoenzymes. Each PP1 complex controls the dephosphorylation of only a small subset of PP1 substrates. We screened the literature for genetically engineered mouse models and identified models for all PP1 isoforms and 104 PIPs. PP1 itself and at least 49 PIPs were connected to human disease-associated phenotypes. Additionally, phenotypes related to 17 PIPs were clearly linked to altered PP1 function, while such information was lacking for 32 other PIPs. We propose structural reverse genetics, which combines structural characterization of proteins with mouse genetics, to identify new PP1-related therapeutic targets. The available mouse models confirm the pleiotropic action of PP1 in health and diseases.