PP2A deactivation is a common event in oral cancer and reactivation by FTY720 shows promising therapeutic potential

A multiscale functional map of somatic mutations in cancer integrating protein structure and network topology

A major goal of cancer biology is to understand the mechanisms underlying tumorigenesis driven by somatically acquired mutations. Two distinct types of computational methodologies have emerged: one focuses on analyzing clustering of mutations within protein sequences and 3D structures, while the other characterizes mutations by leveraging the topology of protein-protein interaction network. Their insights are largely non-overlapping, offering complementary strengths. Here, we established a unified, end-to-end 3D structurally-informed protein interaction network propagation framework, NetFlow3D, that systematically maps the multiscale mechanistic effects of somatic mutations in cancer. The establishment of NetFlow3D hinges upon the Human Protein Structurome, a comprehensive repository we compiled that incorporates the 3D structures of every single protein as well as the binding interfaces of all known protein interactions in humans. NetFlow3D leverages the Structurome to integrate information across atomic, residue, protein and network levels: It conducts 3D clustering of mutations across atomic and residue levels on protein structures to identify potential driver mutations. It then anisotropically propagates their impacts across the protein interaction network, with propagation guided by the specific 3D structural interfaces involved, to identify significantly interconnected network "modules", thereby uncovering key biological processes underlying disease etiology. Applied to 1,038,899 somatic protein-altering mutations in 9,946 TCGA tumors across 33 cancer types, NetFlow3D identified 1,4444 significant 3D clusters throughout the Human Protein Structurome, of which ~55% would not have been found if using only experimentally-determined structures. It then identified 26 significantly interconnected modules that encompass ~8-fold more proteins than applying standard network analyses. NetFlow3D and our pan-cancer results can be accessed from http://netflow3d.yulab.org.

Mitochondria-targeted catalase induced cell malignant transformation by the downregulation of p53 protein stability via USP28/miR-200b/PP2A-Cα axis

Antioxidants exert a paradoxical influence on cancer prevention. The latest explanation for this paradox is the different target sites of antioxidants. However, it remains unclear how mitochondria-targeted antioxidants trigger specific p53-dependent pathways in malignant transformation models. Our study revealed that overexpression of mitochondria-targeted catalase (mCAT) instigated such malignant transformation via mouse double minute 2 homolog (MDM2) -mediated p53 degradation. In mouse epithelial JB6 Cl41 cells, the stable expression of mCAT resulted in MDM2-mediated p53 degradation, unlike in catalase-overexpressed Cl41 cells. Further, we demonstrated that mCAT overexpression upregulated ubiquitin-specific protease 28 (USP28) expression, which in turn stabilized c-Jun protein levels. This alteration initiated the activation of the miR-200b promoter transcription activity and a subsequent increase in miR-200b expression. Furthermore, elevated miR-200b levels then promoted its binding to the 3'-untranslated region of protein phosphatase 2A catalytic subunit (PP2A-C) α-isoform mRNA, consequently resulting in PP2A-C protein downregulation. This cascade of events ultimately contributed to increased MDM2 phosphorylation and p53 protein degradation. Thus, the mCAT overexpression triggers MDM2/p53-dependent malignant transformation through USP28/miR-200b/PP2A-Cα pathway, which may provide a new information for understanding mitochondria-targeted antioxidants facilitate the progression to the tumorigenic state.

TIPRL1 and its ATM-dependent phosphorylation promote radiotherapy resistance in head and neck cancer

PURPOSE

TIPRL1 (target of rapamycin signaling pathway regulator-like 1) is a known interactor and inhibitor of protein phosphatases PP2A, PP4 and PP6 - all pleiotropic modulators of the DNA Damage Response (DDR). Here, we investigated the role of TIPRL1 in the radiotherapy (RT) response of Head and Neck Squamous Cell Carcinoma (HNSCC).

METHODS

TIPRL1 mRNA (cBioportal) and protein expression (immunohistochemistry) in HNSCC samples were linked with clinical patient data. TIPRL1-depleted HNSCC cells were generated by CRISPR/Cas9 editing, and effects on colony growth, micronuclei formation (microscopy), cell cycle (flow cytometry), DDR signaling (immunoblots) and proteome (mass spectrometry) following RT were assessed. Mass spectrometry was used for TIPRL1 phosphorylation and interactomics analysis in irradiated cells.

RESULTS

TIPRL1 expression was increased in tumor versus non-tumor tissue, with high tumoral TIPRL1 expression associating with lower locoregional control and decreased survival of RT-treated patients. TIPRL1 deletion in HNSCC cells resulted in increased RT sensitivity, a faster but prolonged cell cycle arrest, increased micronuclei formation and an altered proteome-wide DDR. Upon irradiation, ATM phosphorylates TIPRL1 at Ser265. A non-phospho Ser265Ala mutant could not rescue the increased radiosensitivity phenotype of TIPRL1-depleted cells. While binding to PP2A-like phosphatases was confirmed, DNA-dependent protein kinase (DNA-PKcs), RAD51 recombinase and nucleosomal histones were identified as novel TIPRL1 interactors. Histone binding, although stimulated by RT, was adversely affected by TIPRL1 Ser265 phosphorylation.

CONCLUSIONS

Our findings underscore a clinically relevant role for TIPRL1 and its ATM-dependent phosphorylation in RT resistance through modulation of the DDR, highlighting its potential as a new HNSCC predictive marker and therapeutic target.

Altering phosphorylation in cancer through PP2A modifiers

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase integral to the regulation of many cellular processes. Due to the deregulation of PP2A in cancer, many of these processes are turned toward promoting tumor progression. Considerable research has been undertaken to discover molecules capable of modulating PP2A activity in cancer. Because PP2A is capable of immense substrate specificity across many cellular processes, the therapeutic targeting of PP2A in cancer can be completed through either enzyme inhibitors or activators. PP2A modulators likewise tend to be effective in drug-resistant cancers and work synergistically with other known cancer therapeutics. In this review, we will discuss the patterns of PP2A deregulation in cancer, and its known downstream signaling pathways important for cancer regulation, along with many activators and inhibitors of PP2A known to inhibit cancer progression.

Combination of berberine and low glucose inhibits gastric cancer through the PP2A/GSK3β/MCL-1 signaling pathway

Intermittent fasting as an adjuvant therapy in clinical practice is an emerging treatment modality to target tumor growth by reducing glucose utilization. Berberine, an alkaloid extracted from the traditional Chinese medicine Coptidis Rhizoma, has been shown to be a safe and effective antitumor agent in several cancers. Hence, the purpose of the present study was to investigate the effects of the combination of berberine and low glucose on gastric cancer. Our results showed that the combination of berberine and low glucose effectively inhibited cell viability, promoted apoptosis, and reduced the migration ability of MGC803 cells. In addition, the combination was shown to activate the PP2A/GSK3β signaling axis, leading to the downregulation of the downstream pro-survival protein MCL-1, which leads to the death of gastric cancer cells. In addition, the inhibitor of GSK3β partially reversed the effect of this combination on MGC803 cells. In vivo experiments demonstrated that berberine effectively impaired the growth of xenograft tumors, when administered during intermittent fasting (hypoglycemic conditions), and was well tolerated by nude mice without the occurrence of any adverse effects. Based on these results, we conclude that the berberine/low-glucose combination can inhibit the growth of gastric cancer through the PP2A/GSK3β/MCL-1 signaling pathway. Accordingly, this combination of drugs and lifestyle may become a new type of safe and effective anti-cancer therapy.

Promising bioactive compounds from the marine environment and their potential effects on various diseases

Background

The marine environment hosts a wide variety of species that have evolved to live in harsh and challenging conditions. Marine organisms are the focus of interest due to their capacity to produce biotechnologically useful compounds. They are promising biocatalysts for new and sustainable industrial processes because of their resistance to temperature, pH, salt, and contaminants, representing an opportunity for several biotechnological applications. Encouraged by the extensive and richness of the marine environment, marine organisms’ role in developing new therapeutic benefits is heading as an arable field.

Main body of the abstract

There is currently much interest in biologically active compounds derived from natural resources, especially compounds that can efficiently act on molecular targets, which are involved in various diseases. Studies are focused on bacteria and fungi, isolated from sediments, seawater, fish, algae, and most marine invertebrates such as sponges, mollusks, tunicates, coelenterates, and crustaceans. In addition to marine macro-organisms, such as sponges, algae, or corals, marine bacteria and fungi have been shown to produce novel secondary metabolites (SMs) with specific and intricate chemical structures that may hold the key to the production of novel drugs or leads. The marine environment is known as a rich source of chemical structures with numerous beneficial health effects. Presently, several lines of studies have provided insight into biological activities and neuroprotective effects of marine algae, including antioxidant, anti-neuroinflammatory, cholinesterase inhibitory activity, and neuronal death inhibition.

Conclusion

The application of marine-derived bioactive compounds has gained importance because of their therapeutic uses in several diseases. Marine natural products (MNPs) display various pharmaceutically significant bioactivities, including antibiotic, antiviral, neurodegenerative, anticancer, or anti-inflammatory properties. The present review focuses on the importance of critical marine bioactive compounds and their role in different diseases and highlights their possible contribution to humanity.

Targeting Sphingolipids for Cancer Therapy

Sphingolipids are an extensive class of lipids with different functions in the cell, ranging from proliferation to cell death. Sphingolipids are modified in multiple cancers and are responsible for tumor proliferation, progression, and metastasis. Several inhibitors or activators of sphingolipid signaling, such as fenretinide, safingol, ABC294640, ceramide nanoliposomes (CNLs), SKI-II, α-galactosylceramide, fingolimod, and sonepcizumab, have been described. The objective of this review was to analyze the results from preclinical and clinical trials of these drugs for the treatment of cancer. Sphingolipid-targeting drugs have been tested alone or in combination with chemotherapy, exhibiting antitumor activity alone and in synergism with chemotherapy in vitro and in vivo. As a consequence of treatments, the most frequent mechanism of cell death is apoptosis, followed by autophagy. Aslthough all these drugs have produced good results in preclinical studies of multiple cancers, the outcomes of clinical trials have not been similar. The most effective drugs are fenretinide and α-galactosylceramide (α-GalCer). In contrast, minor adverse effects restricted to a few subjects and hepatic toxicity have been observed in clinical trials of ABC294640 and safingol, respectively. In the case of CNLs, SKI-II, fingolimod and sonepcizumab there are some limitations and absence of enough clinical studies to demonstrate a benefit. The effectiveness or lack of a major therapeutic effect of sphingolipid modulation by some drugs as a cancer therapy and other aspects related to their mechanism of action are discussed in this review.

Increased Expression of p-GSK3β Predicts Poor Survival in T -III/IV Stage OSCC Patients

BACKGROUND/AIM

Glycogen synthase kinase 3 beta (GSK3-β) acts either as a tumor suppressor or an oncogene in various human cancers. The present study aimed to investigate the expression and activity of p-GSK3-β (Ser9) in oral cancer patients.

MATERIALS AND METHODS

We investigated the levels of p-GSK3β in 152 oral cancer tissues by immunohistochemistry, and explored their prognostic impact.

RESULTS

To investigate the role of p-GSK3β (Ser9) in OSCC progression, we first analyzed the expression levels of protein p-GSK3β in normal and oral cancer tissues using immunohistochemical staining. p-GSK3β immunostaining was detected in 32 of 152 (21.1%) oral cancer specimens. High p-GSK3β expression was significantly associated with T (III/IV) stage. Kaplan-Meier survival analysis revealed that high levels of p-GSK3β were correlated with poor survival (p=0.001) in T stage (III/IV) OSCC patients. Multivariate analyses indicated that TN stage, AJCC tumor stage, tumor differentiation status and clinical therapy, but not p-GSK3β levels, were independent prognostic factors. Significant mortality risk was found in T stage (III/IV) oral cancer patients with high levels of p-GSK3β (p=0.0006).

CONCLUSION

GSK3β inactivation is a key event in oral cancer patients and targeting GSK3β might be valuable in treating oral cancer patients.

PP2AC Phospho-Tyr307 Antibodies Are Not Specific for this Modification but Are Sensitive to Other PP2AC Modifications Including Leu309 Methylation

Protein phosphatase 2A (PP2A) is an important regulator of signal transduction pathways and a tumor suppressor. Phosphorylation of the PP2A catalytic subunit (PP2A_C) at tyrosine 307 has been claimed to inactivate PP2A and was examined in more than 180 studies using commercial antibodies, but this modification was never identified using mass spectrometry. Here we show that the most cited pTyr³⁰⁷ monoclonal antibodies, E155 and F-8, are not specific for phosphorylated Tyr³⁰⁷ but instead are hampered by PP2A_C methylation at leucine 309 or phosphorylation at threonine 304. Other pTyr³⁰⁷ antibodies are sensitive to PP2A_C methylation as well, and some cross-react with pTyr residues in general, including phosphorylated hemagglutinin tags. We identify pTyr³⁰⁷ using targeted mass spectrometry after transient overexpression of PP2A_C and Src kinase. Yet under such conditions, none of the tested antibodies show exclusive pTyr³⁰⁷ specificity. Thus, data generated using these antibodies need to be revisited, and the mechanism of PP2A inactivation needs to be redefined.

The Molecular 'Myc-anisms' Behind Myc-Driven Tumorigenesis and the Relevant Myc-Directed Therapeutics

MYC, a well-studied proto-oncogene that is overexpressed in >20% of tumors across all cancers, is classically known as “undruggable” due to its crucial roles in cell processes and its lack of a drug binding pocket. Four decades of research and creativity led to the discovery of a myriad of indirect (and now some direct!) therapeutic strategies targeting Myc. This review explores the various mechanisms in which Myc promotes cancer and highlights five key therapeutic approaches to disrupt Myc, including transcription, Myc-Max dimerization, protein stability, cell cycle regulation, and metabolism, in order to develop more specific Myc-directed therapies.

Combination of celecoxib and calyculin-A inhibits epithelial-mesenchymal transition in human oral cancer cells

Expression of cyclo-oxygenase-2 (COX-2) and protein phosphatase 2A (PP2A) deactivation occurs frequently in oral squamous cell carcinoma (OSCC). We initially assessed COX-2 and PP2A protein expression in OSCC specimens using immunohistochemical (IHC) staining and western blot analysis. We found strong COX-2 and phosphorylated PP2A (p-PP2A) expression in OSCC samples. No significant difference in total PP2A expression was observed between cancer and nontumor tissues. The effect of combining COX-2 inhibitor and celecoxib (CXB) with the PP2A inhibitor, calyculin-A (CLA) on the OSCC cell line, HSC3, was evaluated in vitro. We found that a combination of 1 nM CLA and 50 µM CXB significantly inhibited cell viability, and migration and invasion of HSC3 cells. Western blots for AKT, p-AKT, ERK, p-ERK, E-cadherin, vimentin and β-catenin were conducted after treatment with CXB and/or CLA. Increased E-cadherin and decreased β-catenin expression were found in CXB or CLA treated hsc-3 cells, whereas the combined CXB and CLA treatment showed no difference in E-cadherin or β-catenin expression. Our findings suggest that CLA alone was more effective than CXB alone, but not in the combined drug treatment.

FTY720 Inhibits MPP+-Induced Microglial Activation by Affecting NLRP3 Inflammasome Activation

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons and excessive microglial activation in the substantia nigra pars compacta (SNpc). In the present study, we aimed to demonstrate the therapeutic effectiveness of the potent sphingosine-1-phosphate receptor antagonist fingolimod (FTY720) in an animal model of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and to identify the potential mechanisms underlying these therapeutic effects. C57BL/6J mice were orally administered FTY720 before subcutaneous injection of MPTP. Open-field and rotarod tests were performed to determine the therapeutic effect of FTY720. The damage to dopaminergic neurons and the production of monoamine neurotransmitters were assessed using immunohistochemistry, high-performance liquid chromatography, and flow cytometry. Immunofluorescence (CD68- positive) and enzyme-linked immunosorbent assay were used to analyze the activation of microglia, and the levels of activated signaling molecules were measured using Western blotting. Our findings indicated that FTY720 significantly attenuated MPTP-induced behavioral deficits, reduced the loss of dopaminergic neurons, and increased dopamine release. FTY720 directly inhibited MPTP-induced microglial activation in the SNpc, suppressed the production of interleukin (IL)-6, IL-1β, and tumor necrosis factor-α in BV-2 microglial cells treated with 1-methyl-4-phenylpyridinium (MPP+), and subsequently decreased apoptosis in SH-SY5Y neuroblastoma cells. Moreover, in MPP+-treated BV-2 cells and primary microglia, FTY720 treatment significantly attenuated the increases in the phosphorylation of PI3K/AKT/GSK-3β, reduced ROS generation and p65 activation, and also inhibited the activation of NLRP3 inflammasome and caspase-1. In conclusion, FTY720 may reduce PD progression by inhibiting NLRP3 inflammasome activation via its effects on ROS generation and p65 activation in microglia. These findings provide novel insights into the mechanisms underlying the therapeutic effects of FTY720, suggesting its potential as a novel therapeutic strategy against PD. Graphical Abstract FTY720 may reduce ROS production by inhibiting the PI3K/AKT/GSK-3β signaling pathway, while at the same time reducing p65 phosphorylation, thus decreasing NLRP3 inflammasome activation through these two pathways, ultimately reducing microglia activation-induced neuronal damage.

Protein phosphatase 2A as a therapeutic target in inflammation and neurodegeneration

Protein phosphatase 2A (PP2A) is a highly complex heterotrimeric enzyme that catalyzes the selective removal of phosphate groups from protein serine and threonine residues. Emerging evidence suggests that it functions as a tumor suppressor by constraining phosphorylation-dependent signalling pathways that regulate cellular transformation and metastasis. Therefore, PP2A-activating drugs (PADs) are being actively sought and investigated as potential novel anti-cancer treatments. Here we explore the concept that PP2A also constrains inflammatory responses through its inhibitory effects on various signalling pathways, suggesting that PADs may be effective in the treatment of inflammation-mediated pathologies.

Chronic Cigarette Smoke Exposure Subdues PP2A Activity by Enhancing Expression of the Oncogene CIP2A

Phosphatase activity of the major serine threonine phosphatase, protein phosphatase 2A (PP2A), is blunted in the airways of individuals with chronic obstructive pulmonary disease (COPD), which results in heightened inflammation and proteolytic responses. The objective of this study was to investigate how PP2A activity is modulated in COPD airways. PP2A activity and endogenous inhibitors of PP2A were investigated in animal and cell models of COPD. In primary human bronchial epithelial (HBE) cells isolated from smokers and donors with COPD, we observed enhanced expression of cancerous inhibitor of PP2A (CIP2A), an oncoprotein encoded by the KIAA1524 gene, compared with cells from nonsmokers. CIP2A expression was induced by chronic cigarette smoke exposure in mice that coincided with a reduction in PP2A activity, airspace enlargements, and loss of lung function, as determined by PP2A phosphatase activity, mean linear intercept analysis, and forced expiratory volume in 0.05 second/forced vital capacity. Modulating CIP2A expression in HBE cells by silencing RNA or chemically with erlotinib enhanced PP2A activity, reduced extracellular-signal-regulated kinase phosphorylation, and reduced the responses of matrix metalloproteinases 1 and 9 in HBE cells isolated from subjects with COPD. Enhanced epithelial growth factor receptor responses in cells from subjects with COPD were observed to modulate CIP2A expression levels. Our study indicates that chronic cigarette smoke induction of epithelial growth factor receptor signaling and CIP2A expression can impair PP2A responses that are associated with loss of lung function and enhancement of proteolytic responses. Augmenting PP2A activity by manipulating CIP2A expression may represent a feasible therapeutic approach to counter smoke-induced lung disease.

Protein Phosphatase 2A Reduces Cigarette Smoke-induced Cathepsin S and Loss of Lung Function

Rationale: CTSS (cathepsin S) is a cysteine protease that is observed at higher concentrations in BAL fluid and plasma of subjects with chronic obstructive pulmonary disease (COPD). Objectives: To investigate whether CTSS is involved in the pathogenesis of cigarette smoke-induced COPD and determine whether targeting upstream signaling could prevent the disease. Methods: CTSS expression was investigated in animal and human tissue and cell models of COPD. Ctss-/- mice were exposed to long-term cigarette smoke and forced oscillation and expiratory measurements were recorded. Animals were administered chemical modulators of PP2A (protein phosphatase 2A) activity. Measurements and Main Results: Here we observed enhanced CTSS expression and activity in mouse lungs after exposure to cigarette smoke. Ctss-/- mice were resistant to cigarette smoke-induced inflammation, airway hyperresponsiveness, airspace enlargements, and loss of lung function. CTSS expression was negatively regulated by PP2A in human bronchial epithelial cells isolated from healthy nonsmokers and COPD donors and in monocyte-derived macrophages. Modulating PP2A expression or activity, with silencer siRNA or a chemical inhibitor or activator, during acute smoke exposure in mice altered inflammatory responses and CTSS expression and activity in the lung. Enhancement of PP2A activity prevented chronic smoke-induced COPD in mice. Conclusions: Our study indicates that the decrease in PP2A activity that occurs in COPD contributes to elevated CTSS expression in the lungs and results in impaired lung function. Enhancing PP2A activity represents a feasible therapeutic approach to reduce CTSS activity and counter smoke-induced lung disease.

PP2A activation alone and in combination with cisplatin decreases cell growth and tumor formation in human HuH6 hepatoblastoma cells

Despite an increase in incidence, treatments for hepatoblastoma remain virtually unchanged for the past 20 years, emphasizing the need for novel therapeutics. FTY720 (fingolimod) is an immunomodulator approved for use in multiple sclerosis in children that has been demonstrated to have anti-cancer properties in multiple cancer types. We have demonstrated that FTY720 activates PP2A in hepatoblastoma, but does not do so via inhibition of the endogenous inhibitors, CIP2A and I2PP2A, as previously observed in other cancers. PP2A activation in hepatoblastoma decreased cell viability, proliferation, and motility and induced apoptosis. In a subcutaneous xenograft model, FTY720 decreased tumor growth. FTY720 in combination with the standard chemotherapeutic, cisplatin, decreased proliferation in a synergistic manner. Finally, animals bearing subcutaneous hepatoblastoma xenografts treated with FTY720 and cisplatin in combination had significantly decreased tumor growth compared to those treated with either drug alone. These findings show that targeting PP2A with FTY70 shows promise in the treatment of hepatoblastoma and that combining FTY720 with cisplatin may be a novel and effective strategy to better treat this devastating pediatric liver tumor.