67-kDa laminin receptor-dependent protein phosphatase 2A (PP2A) activation elicits melanoma-specific antitumor activity overcoming drug resistance

Protein phosphatase 2A modulation and connection with miRNAs and natural products

Protein phosphatase 2A (PP2A), a heterotrimeric holoenzyme (scaffolding, catalytic, and regulatory subunits), regulates dephosphorylation for more than half of serine/threonine phosphosites and exhibits diverse cellular functions. Although several studies on natural products and miRNAs have emphasized their impacts on PP2A regulation, their connections lack systemic organization. Moreover, only part of the PP2A family has been investigated. This review focuses on the PP2A-modulating effects of natural products and miRNAs' interactions with potential PP2A targets in cancer and non-cancer cells. PP2A-modulating natural products and miRNAs were retrieved through a literature search. Utilizing the miRDB database, potential PP2A targets of these PP2A-modulating miRNAs for the whole set (17 members) of the PP2A family were retrieved. Finally, PP2A-modulating natural products and miRNAs were linked via a literature search. This review provides systemic directions for assessing natural products and miRNAs relating to the PP2A-modulating functions in cancer and disease treatments.

Low-Molecular Weight Compounds that Extend the Chronological Lifespan of Yeasts, Saccharomyces cerevisiae, and Schizosaccharomyces pombe

Yeast is an excellent model organism for research for regulating aging and lifespan, and the studies have made many contributions to date, including identifying various factors and signaling pathways related to aging and lifespan. More than 20 years have passed since molecular biological perspectives are adopted in this research field, and intracellular factors and signal pathways that control aging and lifespan have evolutionarily conserved from yeast to mammals. Furthermore, these findings have been applied to control the aging and lifespan of various model organisms by adjustment of the nutritional environment, genetic manipulation, and drug treatment using low-molecular weight compounds. Among these, drug treatment is easier than the other methods, and research into drugs that regulate aging and lifespan is consequently expected to become more active. Chronological lifespan, a definition of yeast lifespan, refers to the survival period of a cell population under nondividing conditions. Herein, low-molecular weight compounds are summarized that extend the chronological lifespan of Saccharomyces cerevisiae and Schizosaccharomyces pombe, along with their intracellular functions. The low-molecular weight compounds are also discussed that extend the lifespan of other model organisms. Compounds that have so far only been studied in yeast may soon extend lifespan in other organisms.

Regulatory effect of Epigallocatechin-3-O-gallate on circular RNA expression in mouse liver

There are few studies on the connection between food components and circular RNA (circRNA), a type of noncoding RNA that is significant for living organisms. (-)-Epigallocatechin-3-O-gallate (EGCG) has been reported to have various biological effects, and elucidation of the molecular mechanism is important for clarifying the functionality of EGCG. In the current study, we looked at how EGCG regulates the expression of circRNA in the liver, which expresses a lot of circRNAs. Mice were given EGCG (10 mg/kg b.w.) orally for one week before circRNA microarray testing was done on their livers. The microarray analysis revealed that mice treated with EGCG had altered expression of 35 circRNAs in their livers. To clarify the function of mmu_circRNA_011775, one of the circRNAs upregulated by EGCG, mouse liver cells after the mmu_circRNA_011775 expression vector was transfected into NMuLi cells, next-generation sequencing (NGS) was used to analyze the gene expression. NGS analysis shows that the expression of the genes responsible for liver fibrosis and inflammation. Gene ontology (GO) analysis showed that mmu_circRNA_011775 changed the meaning of GO terms associated with the cardiovascular system. In the microarray, EGCG altered 35 genes expression. Among them, pre-ribosomal RNA-derived circRNA mmu_circRNA_011775 regulated the expression of various genes related to liver fibrosis and cardiovascular system.

Exploring the composition of protein-ligand binding sites for cancerous inhibitor of PP2A (CIP2A) by inhibitor guided binding analysis: paving a new way for the Discovery of drug candidates against triple negative breast cancer (TNBC)

Triple-negative breast cancer (TNBC) is associated with high-grade invasive carcinoma leading to a 10% to 15% death rate in younger premenopausal women. Targeting cancerous inhibitors of protein phosphatase (CIP2A) has been a highly effective approach for exploring therapeutic drug candidates. Lapatinib, a dual tyrosine kinase inhibitor, has shown promising inhibition properties by inducing apoptosis in TNBC carcinogenesis in vivo. Despite knowledge of the 3D structure of CIP2A, no reports provide insight into CIP2A ligand binding sites. To this effect, we conducted in silico site identification guided by lapatinib binding. Four of the five sites identified were cross-validated, and the stem domain revealed more excellent ligand binding affinity. The binding affinity of lapatinib in these sites was further computed using the Molecular Mechanics/Poisson-Boltzmann Surface Area (MM/PBSA) approach. According to MM/PBSA//200 ns MD simulations, lapatinib exhibited a higher binding affinity against CIP2A in site 2 with ΔG critical values of -37.1 kcal/mol. The steadiness and tightness of lapatinib with CIP2A inside the stem domain disclosed glutamic acid-318 as the culprit amino acid with the highest electrostatic energy. These results provide clear information on the CIP2A domain capable of ligand binding and validate lapatinib as a promising CIP2A inhibitor in TNBC carcinogenesis.

The anti-cancer effect of epigallocatechin-3-O-gallate against multiple myeloma cells is potentiated by 5,7-dimethoxyflavone

(-)-Epigallocatechin-3-O-gallate (EGCG) is one of the major components of green tea polyphenol. Previous studies have shown that EGCG induces cancer-specific cell death in vitro and in vivo without causing severe side effects. However, the anti-cancer effect of EGCG alone is limited. 5,7-dimethoxyflavone (5,7-DMF), one of the principal functional components of black ginger (Kaempferia parviflora), also exerts anti-cancer effects. Here, we show that 5,7-DMF synergistically enhances the anti-cancer effect of EGCG in multiple myeloma cells by potentiating EGCG-induced intracellular cyclic guanosine monophosphate (cGMP) production. Moreover, the combination of EGCG and 5,7-DMF induces apoptotic cell death in multiple myeloma cells, and this is accompanied by activation of the cGMP/acid sphingomyelinase (ASM)/cleaved caspase-3 pathway. In conclusion, we have shown that 5,7-DMF enhances the anti-cancer effect of EGCG by upregulating cGMP in multiple myeloma cells.

67-kDa laminin receptor mediates oolonghomobisflavan B-induced cell growth inhibition in melanoma

BACKGROUND

Oolonghomobisflavans are unique polyphenols found in oolong teas. Oolonghomobisflavan B (OHBFB), a dimer of (-)-epigallocatechin-3-O-gallate (EGCG), is an active compound found in green tea.

PURPOSE

OHBFB has been reported to exert an inhibitory effect on lipase enzyme activity. However, little is known regarding its intercellular signaling induction effect. Further, there are no reports describing the anti-cancer effects of OHBFB.

METHODS

The effect of OFBFB on B16 melanoma cells was evaluated by cell counting, and its mechanisms were determined by western blot analysis with or without protein phosphatase 2A (PP2A) inhibitor treatment. Intracellular cyclic adenosine monophosphate (cAMP) levels were evaluated by time-resolved fluorescence resonance energy transfer analysis. Quartz crystal microbalance (QCM) analysis was performed to assess the binding of OHBFB to 67LR.

RESULTS

Cell growth assay and western blot analyses showed that OHBFB inhibited melanoma cell growth, followed by myosin phosphatase target subunit 1 (MYPT1) and myosin regulatory light chain (MRLC) dephosphorylation via protein phosphatase 2A (PP2A)-dependent mechanisms. These effects are mediated by intracellular cAMP- and protein kinase A (PKA) A-dependent mechanisms. QCM analysis identified the 67-kDa laminin receptor (67LR) as an OHBFB receptor with a Kd of 3.7 µM. We also demonstrated for the first time that OHBFB intake suppresses tumor growth in vivo.

CONCLUSIONS

Taken together, these results indicate that the cAMP/PKA/PP2A/MYPT1/MRLC pathway is a key mediator of melanoma cell growth inhibition following OHBFB binding to 67LR and that OHBFB suppresses tumor growth in vivo.

Epigallocatechin-3-Gallate Therapeutic Potential in Cancer: Mechanism of Action and Clinical Implications

Cellular signaling pathways involved in the maintenance of the equilibrium between cell proliferation and apoptosis have emerged as rational targets that can be exploited in the prevention and treatment of cancer. Epigallocatechin-3-gallate (EGCG) is the most abundant phenolic compound found in green tea. It has been shown to regulate multiple crucial cellular signaling pathways, including those mediated by EGFR, JAK-STAT, MAPKs, NF-κB, PI3K-AKT-mTOR, and others. Deregulation of the abovementioned pathways is involved in the pathophysiology of cancer. It has been demonstrated that EGCG may exert anti-proliferative, anti-inflammatory, and apoptosis-inducing effects or induce epigenetic changes. Furthermore, preclinical and clinical studies suggest that EGCG may be used in the treatment of numerous disorders, including cancer. This review aims to summarize the existing knowledge regarding the biological properties of EGCG, especially in the context of cancer treatment and prophylaxis.

Epigallocatechin gallate restores the reduction of protein phosphatase 2 A subunit B caused by middle cerebral artery occlusion

BACKGROUND

Epigallocatechin gallate (EGCG) is a flavonoid compound commonly found in green tea. It exhibits antioxidant, anti-inflammatory, and neuroprotective effects in cerebral ischemia. Protein phosphatase 2 A (PP2A) is an important serine/threonine phosphatase enzyme involved in various cellular activities. PP2A subunit B is present abundantly in the brain and plays an important role in the nervous system. We investigated the effect of EGCG on the expression level of PP2A subunit B in cerebral ischemia caused by middle cerebral artery occlusion (MCAO). EGCG (50 mg/kg) or vehicle was injected into the peritoneal cavity prior to MCAO surgery. Neurological behavior tests were performed 24 h after MCAO, and right cerebral cortex tissue was collected. Cerebral ischemia caused serious neurological abnormalities, which were alleviated by EGCG administration. We screened the expression of PP2A subunits containing A, B, and C using reverse-transcription PCR. We confirmed that PP2A subunit B exhibited significant changes in MCAO animals compared to subunits A and C. We continuously examined the expression of PP2A subunit B protein in MCAO animals using Western blot analysis.

RESULTS

EGCG alleviated the reduction of PP2A subunit B protein by MCAO damage. In addition, immunohistochemistry demonstrated a decrease in the number of PP2A subunit B-positive cells in the cerebral cortex, and EGCG attenuated this decrease. Maintenance of PP2A subunit B is important for normal brain function.

CONCLUSION

Therefore, our findings suggest that EGCG exerts neuroprotective effects against cerebral ischemia through modulation of PP2A subunit B expression.

Natural biomolecules and derivatives as anticancer immunomodulatory agents

Despite advancements in chemotherapy, the issue of resistance and non-responsiveness to many chemotherapeutic drugs that are currently in clinical use still remains. Recently, cancer immunotherapy has gathered attention as a novel treatment against select cancers. Immunomodulation is also emerging as an effective strategy to improve efficacy. Natural phytochemicals, with known anticancer properties, been reported to mediate their effects by modulating both traditional cancer pathways and immunity. The mechanism of phytochemical mediated-immunomodulatory activity may be attributed to the remodeling of the tumor immunosuppressive microenvironment and the sensitization of the immune system. This allows for improved recognition and targeting of cancer cells by the immune system and synergy with chemotherapeutics. In this review, we will discuss several well-known plant-derived biomolecules and examine their potential as immunomodulators, and therefore, as novel immunotherapies for cancer treatment.

Anticarcinogenic potentials of tea catechins

Catechins are a cluster of polyphenolic bioactive components in green tea. Anticarcinogenic effects of tea catechins have been reported since the 1980s, but it has been controversial. The present paper reviews the advances in studies on the anticarcinogenic activities of tea and catechins, including epidemiological evidence and anticarcinogenic mechanism. Tea catechins showed antagonistic effects on many cancers, such as gynecological cancers, digestive tract cancers, incident glioma, liver and gallbladder cancers, lung cancer, etc. The mechanism underlying the anticarcinogenic effects of catechins involves in inhibiting the proliferation and growth of cancer cells, scavenging free radicals, suppressing metastasis of cancer cells, improving immunity, interacting with other anticancer drugs, and regulating signaling pathways. The inconsistent results and their causes are also discussed in this paper.

Vitamin E functions by association with a novel binding site on the 67 kDa laminin receptor activating diacylglycerol kinase

It is generally recognized that the main function of α-tocopherol (αToc), which is the most active form of vitamin E, is its antioxidant effect, while non-antioxidant effects have also been reported. We previously found that αToc ameliorates diabetic nephropathy via diacylglycerol kinase alpha (DGKα) activation in vivo, and the activation was not related to the antioxidant effect. However, the underlying mechanism of how αToc activates DGKα have been enigmatic. We report that the membrane-bound 67 kDa laminin receptor (67LR), which has previously been shown to serve as a receptor for epigallocatechin gallate (EGCG), also contains a novel binding site for vitamin E, and its association with Vitamin E mediates DGKα activation by αToc. We employed hydrogen-deuterium exchange mass spectrometry (HDX/MS) and molecular dynamics (MD) simulations to identify the specific binding site of αToc on the 67LR and discovered the conformation of the specific hydrophobic pocket that accommodates αToc. Also, HDX/MS and MD simulations demonstrated the detailed binding of EGCG to a water-exposed hydrophilic site on 67LR, while in contrast αToc binds to a distinct hydrophobic site. We demonstrated that 67LR triggers an important signaling pathway mediating non-antioxidant effects of αToc, such as DGKα activation. This is the first evidence demonstrating a membrane receptor for αToc and one of the underlying mechanisms of a non-antioxidant function for αToc.

The Role of Diacylglycerol Kinase in the Amelioration of Diabetic Nephropathy

The drastic increase in the number of patients with diabetes and its complications is a global issue. Diabetic nephropathy, the leading cause of chronic kidney disease, significantly affects patients’ quality of life and medical expenses. Furthermore, there are limited drugs for treating diabetic nephropathy patients. Impaired lipid signaling, especially abnormal protein kinase C (PKC) activation by de novo-synthesized diacylglycerol (DG) under high blood glucose, is one of the causes of diabetic nephropathy. DG kinase (DGK) is an enzyme that phosphorylates DG and generates phosphatidic acid, i.e., DGK can inhibit PKC activation under diabetic conditions. Indeed, it has been proven that DGK activation ameliorates diabetic nephropathy. In this review, we summarize the involvement of PKC and DGK in diabetic nephropathy as therapeutic targets, and its mechanisms, by referring to our recent study.

67-kDa Laminin Receptor-Mediated Cellular Sensing System of Green Tea Polyphenol EGCG and Functional Food Pairing

The body is equipped with a “food factor-sensing system” that senses food factors, such as polyphenols, sulfur-containing compounds, and vitamins, taken into the body, and plays an essential role in manifesting their physiological effects. For example, (–)-epigallocatechin-3-O-gallate (EGCG), the representative catechin in green tea (Camellia sinensi L.), exerts various effects, including anti-cancer, anti-inflammatory, and anti-allergic effects, when sensed by the cell surficial protein 67-kDa laminin receptor (67LR). Here, we focus on three representative effects of EGCG and provide their specific signaling mechanisms, the 67LR-mediated EGCG-sensing systems. Various components present in foods, such as eriodictyol, hesperetin, sulfide, vitamin A, and fatty acids, have been found to act on the food factor-sensing system and affect the functionality of other foods/food factors, such as green tea extract, EGCG, or its O-methylated derivative at different experimental levels, i.e., in vitro, animal models, and/or clinical trials. These phenomena are observed by increasing or decreasing the activity or expression of EGCG-sensing-related molecules. Such functional interaction between food factors is called “functional food pairing”. In this review, we introduce examples of functional food pairings using EGCG.

The Effect of Green Tea as an Adjuvant to Enzyme Replacement Therapy on Oxidative Stress in Fabry Disease: A Pilot Study

Enzymatic replacement therapy (ERT) is not very effective in halting the progression of Fabry disease (FD) toward cardiovascular (CV)-renal remodeling, particularly in case of late diagnosis. FD patients have increased oxidative stress (OS), critical for the induction of CV-renal remodeling. We investigated the effects of an adjuvant antioxidant treatment to ERT on OS and the possible advantages for related complications. OS was evaluated in 10 patients with FD before ERT, after 12 months of ERT, and after 6 months of adjuvant green tea (GT) to ERT by the following experiments: expression of p22^phox; phosphorylation state of MYPT-1 and ERK 1/2 (by western blotting); and quantification of malondialdehyde (MDA) and heme oxygenase (HO)-1 levels (by ELISA). p22^phox and MYPT-1 phosphorylation decreased after ERT and significantly further decreased after GT. ERK 1/2 phosphorylation and MDA levels remained unchanged after ERT, but significantly decreased after GT. HO-1 significantly increased after ERT and further increased after GT. This study provides preliminary data highlighting the antioxidant effect exerted by ERT itself, further amplified by the adjuvant antioxidant treatment with GT. The results of this study provide evidence of the positive effect of early additive antioxidant treatment to reduce OS and prevent/alleviate cardio and cerebrovascular-renal complications related to OS.

(+)-Cyanidan-3-ol inhibits epidermoid squamous cell carcinoma growth via inhibiting AKT/mTOR signaling through modulating CIP2A-PP2A axis

BACKGROUND

Despite recent advances in the treatment of squamous cell skin cancer (SCSC), the disease persists, and treatment resistance develops. Thus, identifying new targets and developing new therapeutic approaches showing low vulnerability to drug resistance is highly needed.

PURPOSE

This study aimed to reveal a novel targeted phytotherapeutic strategy for SCSC treatment alone or in combination with standard targeted anticancer molecules.

STUDY DESIGN

A library of natural products was utilized to identify molecules that inhibit the growth of skin cancer cells. The anticancer potential of the selected compound was evaluated in human skin squamous carcinoma models, in vitro and in vivo. A comprehensive ingenuity pathway analysis (IPA) strategy and molecular biology technology was adopted to investigate the therapeutic mechanisms in human SCSC.

METHODS

The Matrigel invasion chamber, foci formation and soft agar colony formation assays were employed to study the cells invasion and migration potential in vitro. In vivo antitumor effects were evaluated in DMBA/TPA-induced skin papilloma and A431 human skin squamous carcinoma xenograft tumor models. An integrative IPA was employed to identify mechanisms and protein targets in human SCSC.Compounds synergies were determined by the bliss model and evaluated using human SCSC cell lines and xenograft tumors. Histological staining, immunofluorescence imaging, real-time PCR, Western blots, and flow cytometric analyses were employed to analyze apoptosis and cell signaling mechanisms.

RESULTS

We identified (+)-cyanidan-3-ol (CD-3) as a selective compound for inhibiting the growth of SCSC cell lines. CD-3 inhibited tumor growth and burden without apparent toxicity and prolonged the survival of tumor-bearing mice. CD-3 inhibitory effects on SCSC growth are mediated via cell cycle arrest and caspase-dependent apoptosis induction. Mechanistic studies showed that CD-3 activates PP2A via inhibiting CIP2A and produces tumor growth inhibitory effects via promoting dephosphorylation of oncogenic AKT/mTOR signaling proteins in SCSC cells and xenograft tumors in a PP2A dependent manner. Furthermore, the combination of CD-3 and mTOR inhibitors (mTORi) synergistically reduced oncogenic phenotypes.

CONCLUSIONS

Our study suggests that PP2A activation is an effective strategy for SCSC treatment and the CD-3 and mTORi combination may serve as a promising treatment for SCSC.

Ethanol Metabolism in the Liver, the Induction of Oxidant Stress, and the Antioxidant Defense System

The liver metabolizes ethanol through three enzymatic pathways: alcohol dehydrogenase (ADH), cytochrome p450 (also called MEOS), and catalase. Alcohol dehydrogenase class I (ADH1) is considered the most important enzyme for the metabolism of ethanol, MEOS and catalase (CAT) are considered minor alternative pathways. However, contradicting experiments suggest that the non-ADH1 pathway may have a greater relevance for the metabolism of ethanol than previously thought. In some conditions, ethanol is predominately metabolized to acetaldehyde via cytochrome P450 family 2 (CYP2E1), which is involved in the generation of reactive oxygen species (ROS), mainly through electron leakage to oxygen to form the superoxide (O₂^•−) radical or in catalyzed lipid peroxidation. The CAT activity can also participate in the ethanol metabolism that produces ROS via ethanol directly reacting with the CAT-H₂O₂ complex, producing acetaldehyde and water and depending on the H₂O₂ availability, which is the rate-limiting component in ethanol peroxidation. We have shown that CAT actively participates in lactate-stimulated liver ethanol oxidation, where the addition of lactate generates H₂O₂, which is used by CAT to oxidize ethanol to acetaldehyde. Therefore, besides its known role as a catalytic antioxidant component, the primary role of CAT could be to function in the metabolism of xenobiotics in the liver.

Epigallocatechine-3-gallate Inhibits the Adipogenesis of Human Mesenchymal Stem Cells via the Regulation of Protein Phosphatase-2A and Myosin Phosphatase

Epigallocatechin-3-gallate (EGCG) has widespread effects on adipocyte development. However, the molecular mechanisms of EGCG are not fully understood. We investigate the adipogenic differentiation of human-derived mesenchymal stem cells, including lipid deposition and changes in the expression and phosphorylation of key transcription factors, myosin, protein phosphatase-2A (PP2A), and myosin phosphatase (MP). On day 6 of adipogenic differentiation, EGCG (1–20 µM) suppressed lipid droplet formation, which was counteracted by an EGCG-binding peptide for the 67 kDa laminin receptor (67LR), suggesting that EGCG acts via 67LR. EGCG decreased the phosphorylation of CCAAT-enhancer-binding protein beta via the activation of PP2A in a protein kinase A (PKA)-dependent manner, leading to the partial suppression of peroxisome proliferator-activated receptor gamma (PPARγ) and adiponectin expression. Differentiated cells exhibited a rounded shape, cortical actin filaments, and lipid accumulation. The EGCG treatment induced cell elongation, stress fiber formation, and less lipid accumulation. These effects were accompanied by the degradation of the MP target subunit-1 and increased the phosphorylation of the 20 kDa myosin light chain. Our results suggest that EGCG acts as an agonist of 67LR to inhibit adipogenesis via the activation of PP2A and suppression of MP. These events are coupled with the decreased phosphorylation and expression levels of adipogenic transcription factors and changes in cell shape, culminating in curtailed adipogenesis.

Versatile polyphenolic platforms in regulating cell biology

Polyphenolic materials are a class of fascinating and versatile bioinspired materials for biointerfacial engineering. In particular, due to the presence of active chemical groups, a series of unique physicochemical properties become accessible and tunable of the as-prepared polyphenolic platforms, which could delicately regulate the cell activities via cell-material contact-dependent interactions. More interestingly, polyphenols could also affect the cell behaviors via cell-material contact-independent manner, which arise due to their intrinsically functional characteristics (e.g., antioxidant and photothermal behaviors). As such, a comprehensive understanding on the relationship between material properties and desired biomedical applications, as well as the underlying mechanism at the cellular and molecular level would provide material design principles and accelerate the lab-to-clinic translation of polyphenolic platforms. In this review, we firstly give a brief overview of cell hallmarks governed by surrounding cues, followed by the introduction of polyphenolic material engineering strategies. Subsequently, a detailed discussion on cell-polyphenols contact-dependent interfacial interaction and contact-independent interaction was also carefully provided. Lastly, their biomedical applications were elaborated. We believe that this review could provide guidances for the rational material design of multifunctional polyphenols and extend their application window.

Theaflavin-3,3'-di-gallate represses prostate cancer by activating the PKCδ/aSMase signaling pathway through a 67 kDa laminin receptor

Prostate cancer is a major cause of morbidity and mortality in men. Theaflavin-3,3'-digallate (TF-3) is an important functional ingredient of black tea. We aimed to evaluate the cytotoxic effects of TF-3 on prostate cancer and to identify the underlying molecular mechanism. In this study, we explored the effects of TF-3 on prostate cancer in PC-3 cells and in NOD/SCID mice with prostate cancer. The results demonstrated that TF-3 inhibited prostate cancer cell proliferation by regulating the PKCδ/aSMase signaling pathway. The anti-prostate cancer effect of TF-3 was attributed to the expression of the 67 kDa laminin receptor (67LR), which is overexpressed in various cancers, playing a vital role in the growth and metastasis of tumor cells. Stable knockdown of 67LR could efficiently inhibit TF-3 induced apoptosis and cell cycle arrest in PC-3 cells, through interacting with the PKCδ/aSMase signaling pathway. In vivo studies also confirmed the above findings that TF-3 effectively inhibited tumor growth in terms of tumor volume. TF-3 treatment can significantly inhibit tumor growth and up-regulate the phosphorylation of PKCδ and the expression of aSMase in tumor xenografts developed by subcutaneously implanting PC-3 cells and 67LR-overexpressing PC-3 cells in mice. However, in tumor xenografts formed by subcutaneously implanting 67LR-knockdown PC-3 cells, TF-3 has no significant effect on PKCδ/aSMase pathway regulation and tumor growth inhibition.

Fustin, a Flavanonol, Synergically Potentiates the Anticancer Effect of Green Tea Catechin Epigallocatechin-3-O-Gallate with Activation of the eNOS/cGMP Axis

Epigallocatechin-3-O-gallate (EGCG), a catechin present in green tea, selectively elicits apoptosis in multiple myeloma cells by activating the endothelial nitric oxide synthase (eNOS)/cyclic guanosine monophosphate (cGMP) axis. However, the effects of EGCG alone are limited. Herein, we revealed that fustin, a flavanonol, enhances the EGCG-elicited activation of the cGMP/eNOS axis in multiple myeloma cells. Isobologram analysis demonstrated that EGCG/fustin synergistically elicited cell death in multiple myeloma cells. Importantly, this chemical combination significantly promoted cell death without affecting the normal cells. To assess the effects of EGCG and fustin in vivo, female BALB/c mice were inoculated with multiple myeloma MPC11 cells and then treated with each compound. The combination of EGCG/fustin suppressed tumor growth in vivo without affecting alanine aminotransferase/aspartate aminotransferase levels, the dose-limiting toxicity of EGCG. Consistent with in vitro findings, this combination increased eNOS phosphorylation at Ser1177 in the tumor. Collectively, fustin amplified EGCG-induced activation of the eNOS/cGMP axis.

p21-Activated kinase 1 (PAK1) in aging and longevity: An overview

The p21-activated kinases (PAKs) belong to serine/threonine kinases family, regulated by ∼21 kDa small signaling G proteins RAC1 and CDC42. The mammalian PAK family comprises six members (PAK1-6) that are classified into two groups (I and II) based on their domain architecture and regulatory mechanisms. PAKs are implicated in a wide range of cellular functions. PAK1 has recently attracted increasing attention owing to its involvement in oncogenesis, tumor progression, and metastasis as well as several life-limiting diseases and pathological conditions. In Caenorhabditis elegans, PAK1 functions limit the lifespan under basal conditions by inhibiting forkhead transcription factor DAF-16. Interestingly, PAK depletion extended longevity and attenuated the onset of age-related phenotypes in a premature-aging mouse model and delayed senescence in mammalian fibroblasts. These observations implicate PAKs as not only oncogenic but also aging kinases. Therefore, PAK-targeting genetic and/or pharmacological interventions, particularly PAK1-targeting, could be a viable strategy for developing cancer therapies with relatively no side effects and promoting healthy longevity. This review describes PAK family proteins, their biological functions, and their role in regulating aging and longevity using C. elegans. Moreover, we discuss the effect of small-molecule PAK1 inhibitors on the lifespan and healthspan of C. elegans.

LAMR1 restricts Zika virus infection by attenuating the envelope protein ubiquitination

Zika virus (ZIKV) infection can cause severe neurological disorders, including Guillain–Barre syndrome and meningoencephalitis in adults and microcephaly in fetuses. Here, we reveal that laminin receptor 1 (LAMR1) is a novel host resistance factor against ZIKV infection. Mechanistically, we found that LAMR1 binds to ZIKV envelope (E) protein via its intracellular region and attenuates E protein ubiquitination through recruiting the deubiquitinase eukaryotic translation initiation factor 3 subunit 5 (EIF3S5). We further found that the conserved G282 residue of E protein is essential for its interaction with LAMR1. Moreover, a G282A substitution abolished the binding of E protein to LAMR1 and inhibited LAMR1-mediated E protein deubiquitination. Together, our results indicated that LAMR1 represses ZIKV infection through binding to E protein and attenuating its ubiquitination.

The interaction of SET and protein phosphatase 2A as target for cancer therapy

In cancer cells, tumor suppressor proteins loss-of-function are usually the result of genetic mutations. Protein Phosphatase 2A is a tumor suppressor that inactivates several signaling pathways through removal of phosphate residues important for other proteins stability and/or activation. Different from other tumor suppressors, PP2A is, in many cancer types, inactivated by endogenous inhibitors. In physiological conditions, these inhibitors are important to balance PP2A activity. However, in cancer cells, overexpression of these inhibitors can keep PP2A inactive, resulting in sustained activation of mitogenic signaling pathways and transcription factors, metabolic reprogramming, with the resulting cancer progression and the resistance to anti-cancer therapies. One of these endogenous inhibitors is the protein SET (SE Translocation). SET is a multifunctional protein, which high expression has been associated with several types of cancer, as well as other diseases such as Alzheimer's disease. Disruption of the interaction between SET and PP2A to rescue the activity of PP2A may represent a new therapeutic strategy and opportunity for cancer treatment. This review brings up-to-date advances on the interactions between SET and PP2A and their biological consequences. Moreover, we review reported inhibitors of SET-PP2A interaction under investigation as therapeutic opportunities for the treatment of cancers.

Activation of Myosin Phosphatase by Epigallocatechin-Gallate Sensitizes THP-1 Leukemic Cells to Daunorubicin

BACKGROUND

The Myosin Phosphatase (MP) holoenzyme is composed of a Protein Phosphatase type 1 (PP1) catalytic subunit and a regulatory subunit termed Myosin Phosphatase Target subunit 1 (MYPT1). Besides dephosphorylation of myosin, MP has been implicated in the control of cell proliferation via dephosphorylation and activation of the tumor suppressor gene products, retinoblastoma protein (pRb) and merlin. Inhibition of MP was shown to attenuate the drug-induced cell death of leukemic cells by chemotherapeutic agents, while activation of MP might have a sensitizing effect.

OBJECTIVE

Recently, Epigallocatechin-Gallate (EGCG), a major component of green tea, was shown to activate MP by inducing the dephosphorylation of MYPT1 at phospho-Thr696 (MYPT1^pT696), which might confer enhanced chemosensitivity to cancer cells.

METHODS

THP-1 leukemic cells were treated with EGCG and Daunorubicin (DNR) and cell viability was analyzed. Phosphorylation of tumor suppressor proteins was detected by Western blotting.

RESULTS

EGCG or DNR (at sub-lethal doses) alone had moderate effects on cell viability, while the combined treatment caused a significant decrease in the number of viable cells by enhancing apoptosis and decreasing proliferation. EGCG plus DNR decreased the phosphorylation level of MYPT1^pT696, which was accompanied by prominent dephosphorylation of pRb. In addition, significant dephosphorylation of merlin was observed when EGCG and DNR were applied together.

CONCLUSION

Our results suggest that EGCG-induced activation of MP might have a regulatory function in mediating the chemosensitivity of leukemic cells via dephosphorylation of tumor suppressor proteins.

Chitosan coated pH-responsive metal-polyphenol delivery platform for melanoma chemotherapy

The safe and effective drug delivery system is important for cancer therapy. Here in, we first constructed a delivery system Cabazitaxel(Cab)@MPN/CS between metal-polyphenol (MPN) and chitosan (CS) to deliver Cab for melanoma therapy. The preparation process is simple, green, and controllable. After introducing CS coating, the drug loading was improved from 7.56 % to 9.28 %. Cab@MPN/CS NPs released Cab continuously under acid tumor microenvironment. The zeta potential of Cab@MPN/CS NPs could be controlled by changing the ratio of Cab@MPN and CS solutions. The positively charged Cab@MPN/CS accelerate B16F10 cell internalization. After internalized, Cab@MPN/CS NPs could escape from lysosomes via the proton sponge effect. The permeability of CS promotes the penetration of Cab@MPN/CS to the deeper B16F10 tumor spheroids. In vivo results showed that Cab@MPN/CS NPs have a longer retention time in tumor tissues and significantly inhibit tumor growth by up-regulating TUNEL expression and down-regulating KI67 and CD31 expression. Thus, this delivery system provides a promising strategy for the tumor therapy in clinic.

Myosin Phosphatase Is Implicated in the Control of THP-1 Monocyte to Macrophage Differentiation

Monocyte to macrophage differentiation is characterized by the activation of various signal transduction pathways, which may be modulated by protein phosphorylation; however, the impact of protein kinases and phosphatases is not well understood yet. It has been demonstrated that actomyosin rearrangement during macrophage differentiation is dependent on Rho-associated protein kinase (ROCK). Myosin phosphatase (MP) target subunit-1 (MYPT1) is one of the major cellular substrates of ROCK, and MP is often a counter enzyme of ROCK; therefore, MP may also control macrophage differentiation. Changes in MP activity and the effects of MP activation were studied on PMA or l,25(OH)₂D₃-induced differentiation of monocytic THP-1 cells. During macrophage differentiation, phosphorylation of MYPT1 at Thr696 and Thr853 increased significantly, resulting in inhibition of MP. The ROCK inhibitor H1152 and the MP activator epigallocatechin-3-gallate (EGCG) attenuated MYPT1 phosphorylation and concomitantly decreased the extent of phosphorylation of 20 kDa myosin light chain. H1152 and EGCG pretreatment also suppressed the expression of CD11b and weakened the PMA-induced adherence of the cells. Our results indicate that MP activation/inhibition contributes to the efficacy of monocyte to macrophage differentiation, and this enzyme may be a target for pharmacological interventions in the control of disease states that are affected by excessive macrophage differentiation.

Src Mediates Epigallocatechin-3-O-Gallate-Elicited Acid Sphingomyelinase Activation

Epigallocatechin-3-O-gallate (EGCG) is one of the major bioactive compounds known to be present in green tea. We previously reported that EGCG shows selective toxicity through activation of the protein kinase B (Akt)/cyclic guanosine monophosphate (cGMP)/acid sphingomyelinase (ASM) axis via targeting its receptor 67-kDa laminin receptor (67LR), which is overexpressed in cancer. However, little is known about upstream mechanisms of EGCG-elicited ASM activation. In this study we show that the proto-oncogene tyrosine-protein kinase Src, also known as c-src, plays a crucial role in the anticancer effect of EGCG. We showed that EGCG elicits phosphorylation of Src at Tyr 416, a crucial phosphorylation site for its activity, and that the pharmacological inhibition of Src impedes the upstream events in EGCG-induced cell death signaling including upregulation of Akt activity, increase in cGMP levels, and activation of ASM. Moreover, focal adhesion kinase (FAK), which is involved in the phosphorylation of Src, is colocalized with 67LR. EGCG treatment enhanced interaction of FAK and 67LR. Consistent with these findings, pharmacological inhibition of FAK significantly neutralized EGCG-induced upregulation of Akt activity and activation of ASM. Taken together, FAK/Src play crucial roles in the upstream signaling of EGCG.

Mechanisms of Acquired BRAF Inhibitor Resistance in Melanoma: A Systematic Review

This systematic review investigated the literature on acquired v-raf murine sarcoma viral oncogene homolog B1 (BRAF) inhibitor resistance in patients with melanoma. We searched MEDLINE for articles on BRAF inhibitor resistance in patients with melanoma published since January 2010 in the following areas: (1) genetic basis of resistance; (2) epigenetic and transcriptomic mechanisms; (3) influence of the immune system on resistance development; and (4) combination therapy to overcome resistance. Common resistance mutations in melanoma are BRAF splice variants, BRAF amplification, neuroblastoma RAS viral oncogene homolog (NRAS) mutations and mitogen-activated protein kinase kinase 1/2 (MEK1/2) mutations. Genetic and epigenetic changes reactivate previously blocked mitogen-activated protein kinase (MAPK) pathways, activate alternative signaling pathways, and cause epithelial-to-mesenchymal transition. Once BRAF inhibitor resistance develops, the tumor microenvironment reverts to a low immunogenic state secondary to the induction of programmed cell death ligand-1. Combining a BRAF inhibitor with a MEK inhibitor delays resistance development and increases duration of response. Multiple other combinations based on known mechanisms of resistance are being investigated. BRAF inhibitor-resistant cells develop a range of 'escape routes', so multiple different treatment targets will probably be required to overcome resistance. In the future, it may be possible to personalize combination therapy towards the specific resistance pathway in individual patients.

The mechanisms of ameliorating effect of a green tea polyphenol on diabetic nephropathy based on diacylglycerol kinase α

Significant efforts have been made to ameliorate diabetic nephropathy (DN) by inhibiting protein kinase C. However, these efforts have not been successful in human trials, suggesting that novel therapeutic strategies are required. Thus far, it has been reported that green tea polyphenol epigallocatechin gallate (EGCg) improved albuminuria in DN in a human trial. Our previous study revealed that activation of diacylglycerol kinase α (DGKα) plays a crucial role in the amelioration of DN and that EGCg activates DGKα. Here, we investigated whether and how DGKα contributes to the amelioration of DN upon stimulation by EGCg by using streptozotocin-induced type 1 diabetic model mice. Our results revealed that EGCg ameliorated albuminuria in DN through DGKα in vivo, and methylated EGCg, which has higher absorption in the plasma improved albuminuria in DN effectively. Additionally, we showed that c-Src mediated EGCg-induced DGKα translocation and colocalized with the 67 kDa laminin receptor, which is an EGCg receptor. Furthermore, EGCg attenuated the loss of podocytes in DN by preventing a decrease in focal adhesion under high glucose conditions. Our results indicate that the DGKα pathway is an attractive therapeutic target and that activating this pathway is a novel strategy for treating DN.

Sanggenol L promotes apoptotic cell death in melanoma skin cancer cells through activation of caspase cascades and apoptosis-inducing factor

Sanggenol L is one component of root bark of Morus alba. The molecular and cellular mechanisms of sanggenol L effects on melanoma cells are not well known. Recently, melanoma is the most common skin cancer with a high mortality rate not only in United States, but also in East Asia. Therefore, safe and effective treatments for melanoma treatment are required. In this study, we investigated whether or not sanggenol L possesses anti-cancer activity in human and mouse melanoma skin cancer cells. Sanggenol L treatment exerted significant cell growth inhibitory effects and inhibited colony formation capacity against B16, SK-MEL-2, and SK-MEL-28 melanoma skin cancer cells, whereas HaCaT human epithelial keratinocyte cells was unaffected by sanggenol L treatment. Sanggenol L treatment resulted in apoptotic cell death in melanoma skin cancer cells, which was characterized by accumulation of apoptotic cells, nuclear condensation, and apoptotic bodies. We also showed that sanggenol L treatment induced caspase-dependent apoptosis (up-regulation of Bax and cleaved-PARP or down-regulation of Bid, Bcl-2, procaspse-3, -8, and -9), induction of caspase-independent apoptosis (up-regulation of AIF and Endo G on cytosol) in melanoma skin cancer cells. These results suggest that sanggenol L induces caspase-dependent and -independent apoptosis in melanoma skin cancer cells.

Procyanidin C1 Inhibits Melanoma Cell Growth by Activating 67-kDa Laminin Receptor Signaling

SCOPE

Procyanidin C1 (PC1) is an epicatechin trimer found mainly in grapes that is reported to provide several health benefits. However, little is known about the molecular mechanisms underlying these benefits. The aim of this study is to demonstrate the molecular mechanisms by which PC1 operates.

METHODS AND RESULTS

A 67-kDa laminin receptor (67LR) is identified as a cell surface receptor of PC1, with a Kd value of 2.8 µm. PC1 induces an inhibitory effect on growth, accompanied by dephosphorylation of the C-kinase potentiated protein phosphatase-1 inhibitor protein of 17 kDa (CPI17) and myosin regulatory light chain (MRLC) proteins, followed by actin cytoskeleton remodeling in melanoma cells. These actions are mediated by protein kinase A (PKA) and protein phosphatase 2A (PP2A) activation once PC1 is bound to 67LR.

CONCLUSION

It is demonstrated that PC1 elicits melanoma cell growth inhibition by activating the 67LR/PKA/PP2A/CPI17/MRLC pathway.

Epigallocatechin-3-O-gallate induces acid sphingomyelinase activation through activation of phospholipase C

Epigallocatechin-3-O-gallate (EGCG)-induced cyclic guanosine monophosphate (cGMP) plays a crucial role in EGCG-induced cell death in various types of cancer cells. However, little is known regarding the early molecular events after cGMP induction. In this study, we showed that cGMP induction is sufficient to induce the phosphorylation of protein kinase C delta (PKCδ) at Ser664, the crucial kinase for EGCG-induced activation of acid sphingomyelinase (ASM). Using a chemical inhibitor library, we revealed that the inhibitors of the negative regulators of diacylglycerol strongly increase the effect of EGCG. We also showed that EGCG treatment increased phospholipase C (PLC) activity, and the same results were obtained with cGMP inducer treatment. EGCG-induced ASM activation was completely suppressed by pharmacological inhibition of PLC. Collectively, EGCG-induced cGMP activated the cGMP/PLC/PKCδ/ASM signaling axis in multiple myeloma cells.

Unraveling the molecular mechanisms and the potential chemopreventive/therapeutic properties of natural compounds in melanoma

Melanoma is the most fatal form of skin cancer. Current therapeutic approaches include surgical resection, chemotherapy, targeted therapy and immunotherapy. However, these treatment strategies are associated with development of drug resistance and severe side effects. In recent years, natural compounds have also been extensively studied for their anti-melanoma effects, including tumor growth inhibition, apoptosis induction, angiogenesis and metastasis suppression and cancer stem cell elimination. Moreover, a considerable number of studies reported the synergistic activity of phytochemicals and standard anti-melanoma agents, as well as the enhanced effectiveness of their synthetic derivatives and novel formulations. However, clinical data confirming these promising effects in patients are still scanty. This review emphasizes the anti-tumor mechanisms and potential application of the most studied natural products for melanoma prevention and treatment.

ITGA6 and RPSA synergistically promote pancreatic cancer invasion and metastasis via PI3K and MAPK signaling pathways

Pancreatic cancer is one of the most malignant tumors. Invasion and metastasis can occur in the early stage of pancreatic cancer, contributing to the poor prognosis. Accordingly, in this study, we evaluated the molecular mechanisms underlying invasion and metastasis. Using mass spectrometry, we found that Integrin alpha 6 (ITGA6) was more highly expressed in a highly invasive pancreatic cancer cell line (PC-1.0) than in a less invasive cell line (PC-1). Through in vitro and in vivo experiments, we observed significant decreases in invasion and metastasis in pancreatic cancer cells after inhibiting ITGA6. Based on data in TCGA, high ITGA6 expression significantly predicted poor prognosis. By using Co-IP combined mass spectrometry, we found that ribosomal protein SA (RPSA), which was also highly expressed in PC-1.0, interacted with ITGA6. Similar to ITGA6, high RPSA expression promoted invasion and metastasis and indicated poor prognosis. Interestingly, although ITGA6 and RPSA interacted, they did not mutually regulate each other. ITGA6 and RPSA affected invasion and metastasis via the PI3K and MAPK signaling pathways, respectively. Inhibiting ITGA6 significantly reduced the expression of p-AKT, while inhibiting RPSA led to the downregulation of p-ERK1/2. Compared with the inhibition of ITGA6 or RPSA alone, the downregulation of both ITGA6 and RPSA weakened invasion and metastasis to a greater extent and led to the simultaneous downregulation of p-AKT and p-ERK1/2. Our research indicates that the development of drugs targeting both ITGA6 and RPSA may be an effective strategy for the treatment of pancreatic cancer.

Inhibition of protein phosphatase-1 and -2A by ellagitannins: structure-inhibitory potency relationships and influences on cellular systems

Several ellagitannins inhibited the activity of protein phosphatase-1 (PP1) and -2 A (PP2A) catalytic subunits (PP1c and PP2Ac) with preferential suppression of PP1c over PP2Ac. The inhibitory potency for PP1c followed the order of tellimagrandin I > mahtabin A > praecoxin B > 1.2-Di-O-galloyl-4.6-(S)-HHDP-β-D-glucopyranose > pedunculagin with IC₅₀ values ranging from 0.20 µM to 2.47 µM. The interaction of PP1c and tellimagrandin I was assessed by NMR saturation transfer difference, surface plasmon resonance, isothermal titration calorimetry, and microscale thermophoresis based binding techniques. Tellimagrandin I suppressed viability and phosphatase activity of HeLa cells, while mahtabin A was without effect. Conversely, mahtabin A increased the phosphorylation level of SNAP-25^Thr138 and suppressed exocytosis of cortical synaptosomes, whereas tellimagrandin I was without influence. Our results establish ellagitannins as partially selective inhibitors of PP1 and indicate that these polyphenols may act distinctly in cellular systems depending on their membrane permeability and/or their actions on cell membranes.

Molecular Targets of Epigallocatechin-Gallate (EGCG): A Special Focus on Signal Transduction and Cancer

Green tea is a beverage that is widely consumed worldwide and is believed to exert effects on different diseases, including cancer. The major components of green tea are catechins, a family of polyphenols. Among them, epigallocatechin-gallate (EGCG) is the most abundant and biologically active. EGCG is widely studied for its anti-cancer properties. However, the cellular and molecular mechanisms explaining its action have not been completely understood, yet. EGCG is effective in vivo at micromolar concentrations, suggesting that its action is mediated by interaction with specific targets that are involved in the regulation of crucial steps of cell proliferation, survival, and metastatic spread. Recently, several proteins have been identified as EGCG direct interactors. Among them, the trans-membrane receptor 67LR has been identified as a high affinity EGCG receptor. 67LR is a master regulator of many pathways affecting cell proliferation or apoptosis, also regulating cancer stem cells (CSCs) activity. EGCG was also found to be interacting directly with Pin1, TGFR-II, and metalloproteinases (MMPs) (mainly MMP2 and MMP9), which respectively regulate EGCG-dependent inhibition of NF-kB, epithelial-mesenchimal transaction (EMT) and cellular invasion. EGCG interacts with DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), which modulates epigenetic changes. The bulk of this novel knowledge provides information about the mechanisms of action of EGCG and may explain its onco-suppressive function. The identification of crucial signalling pathways that are related to cancer onset and progression whose master regulators interacts with EGCG may disclose intriguing pharmacological targets, and eventually lead to novel combined treatments in which EGCG acts synergistically with known drugs.

Metabolomics of Green-Tea Catechins on Vascular-Endothelial-Growth-Factor-Stimulated Human-Endothelial-Cell Survival

Neovascularization causes serious oculopathy related to upregulation of vascular-endothelial-growth factor (VEGF) causing new capillary growth via endothelial cells. Green-tea-extract (GTE) constituents possess antiangiogenesis properties. We used VEGF to induce human umbilical-vein endothelial cells (HUVECs) and applied GTE, epigallocatechin gallate (EGCG), and mixtures of different compositions of purified catechins (M1 and M2) to evaluate their efficacies of inhibition and their underlying mechanisms using cell-cycle analysis and untargeted metabolomics techniques. GTE, EGCG, M1, and M2 induced HUVEC apoptosis by 22.1 ± 2, 20.0 ± 0.7, 50.7 ± 8.5, and 69.8 ± 4.1%, respectively. GTE exerted a broad, balanced metabolomics spectrum, involving suppression of the biosynthesis of cellular building blocks and oxidative-phosphorylation metabolites as well as promotion of the biosynthesis of membrane lipids and growth factors. M2 mainly induced mechanisms associated with energy and biosynthesis suppression. Therefore, GTE exerted mechanisms involving both promotion and suppression activities, whereas purified catechins induced extensive apoptosis. GTE could be a more promising antineovascularization remedy for ocular treatment.

Myosin phosphatase: Unexpected functions of a long-known enzyme

Myosin phosphatase (MP) holoenzyme is a Ser/Thr specific enzyme, which is the member of protein phosphatase type 1 (PP1) family and composed of a PP1 catalytic subunit (PP1c/PPP1CB) and a myosin phosphatase targeting subunit (MYPT1/PPP1R12A). PP1c is required for the catalytic activity of the holoenzyme, while MYPT1 regulates MP through targeting the holoenzyme to its substrates. Above the well-characterized function of MP, as the major regulator of smooth muscle contractility mediating the dephosphorylation of 20 kDa myosin light chain, accumulating data support its role in other, non-contractile functions. In this review, we summarize the scaffold function of MP holoenzyme and its roles in processes such as cell cycle, development, gene expression regulation and neurotransmitter release. In particular, we highlight novel interacting proteins of MYPT1 and pathophysiological functions of MP relevant to tumorigenesis, insulin resistance and neurodegenerative disorders. This article is part of a Special Issue entitled: Protein Phosphatases as Critical Regulators for Cellular Homeostasis edited by Prof. Peter Ruvolo and Dr. Veerle Janssens.

Polyphyllin I inhibits invasion and epithelial-mesenchymal transition via CIP2A/PP2A/ERK signaling in prostate cancer

Polyphyllin I (PPI) is a natural compound extracted from the rhizomes of Paris polyphylla and has been used to treat fevers and headaches in China. In the present study, the antitumor activity of PPI in prostate cancer (PC) cells was evaluated. At low doses, PPI decreased proliferation, invasion and epithelial-mesenchymal transition (EMT) in PC cells. PPI decreased the expression of matrix metalloproteinase 7 (MMP7), an enzyme that is critical for tumor metastasis. PPI also decreased the expression of Snail and vimentin, which are EMT-associated factors. Additionally, PPI suppressed AP-1 transcriptional activity and AP-1 binding to the MMP7 and vimentin promoters. The results demonstrated that PPI downregulated the phosphorylation of extracellular signaling‑related kinase (ERK), which is upstream modulator of AP-1. The results of the present study demonstrated that PPI may inhibit the cancerous inhibitor of protein phosphatase 2A (CIP2A)/protein phosphatase 2A (PP2A)/ERK axis, downregulate the expression of MMP7, vimentin, and Snail, and suppress tumor invasion and EMT. A PC xenograft mouse model was employed and the results revealed that PPI may decrease tumor growth and weight. Additionally, PPI may inhibit proliferating cell nuclear antigen expression and CIP2A/PP2A/ERK signaling pathway in PPI-treated tumors. Therefore, the results of the present study suggest that PPI may suppress the growth, invasion and EMT of PC cells via inhibition of CIP2A/PP2A/ERK signaling axis. As a result, PPI may be a novel target for the treatment of PC.

NADPH Oxidases and Their Roles in Skin Homeostasis and Carcinogenesis

SIGNIFICANCE

Skin protects the body from dehydration, pathogens, and external mutagens. NADPH oxidases are central components for regulating the cellular redox balance. There is increasing evidence indicating that reactive oxygen species (ROS) generated by members of this enzyme family play important roles in the physiology and pathophysiology of the skin. Recent Advances: NADPH oxidases are active producers of ROS such as superoxide and hydrogen peroxide. Different isoforms are found in virtually all tissues. They play pivotal roles in normal cell homeostasis and in the cellular responses to various stressors. In particular, these enzymes are integral parts of redox-sensitive prosurvival and proapoptotic signaling pathways, in which they act both as effectors and as modulators. However, continuous (re)activation of NADPH oxidases can disturb the redox balance of cells, in the worst-case scenario in a permanent manner. Abnormal NADPH oxidase activity has been associated with a wide spectrum of diseases, as well as with aging and carcinogenesis.

CRITICAL ISSUES

Sunlight with its beneficial and deleterious effects induces the activation of NADPH oxidases in the skin. Evidence for the important roles of this enzyme family in skin cancer and skin aging, as well as in many chronic skin diseases, is now emerging.

FUTURE DIRECTIONS

Understanding the precise roles of NADPH oxidases in normal skin homeostasis, in the cellular responses to solar radiation, and during carcinogenesis will pave the way for their validation as therapeutic targets not only for the prevention and treatment of skin cancers but also for many other skin-related disorders. Antioxid. Redox Signal. 28, 1238-1261.

A dock derived compound against laminin receptor (37 LR) exhibits anti-cancer properties in a prostate cancer cell line model

Laminin receptor (67 LR) is a 67 kDa protein derived from a 37 kDa precursor (37 LR). 37/67 LR is a strong clinical correlate for progression, aggression, and chemotherapeutic relapse of several cancers including breast, prostate, and colon. The ability of 37/67 LR to promote cancer cell aggressiveness is further increased by its ability to transduce physiochemical and mechanosensing signals in endothelial cells and modulate angiogenesis. Recently, it was demonstrated that 37/67 LR modulates the anti-angiogenic potential of the secreted glycoprotein pigment epithelium-derived factor (PEDF). Restoration of PEDF balance is a desirable therapeutic outcome, and we sought to identify a small molecule that could recapitulate known signaling properties of PEDF but without the additional complications of peptide formulation or gene delivery safety validation. We used an in silico drug discovery approach to target the interaction interface between PEDF and 37 LR. Following cell based counter screening and binding validation, we characterized a hit compound's anti-viability, activation of PEDF signaling-related genes, anti-wound healing, and anti-cancer signaling properties. This hit compound has potential for future development as a lead compound for treating tumor growth and inhibiting angiogenesis.

Green Tea Polyphenol EGCG Upregulates Tollip Expression by Suppressing Elf-1 Expression

TLR signaling is critical to innate immune system regulation; however, aberrant TLR signaling is involved in several diseases, including insulin resistance, Alzheimer's disease, and tumor metastasis. Moreover, a recent study found that TLR-4 signaling pathway inhibition might be a target for the suppression of chronic inflammatory disorders. In this article, we show that the green tea polyphenol epigallocatechin-3-O-gallate (EGCG) increases the expression of Toll interacting protein, a strong inhibitor of TLR4 signaling, by suppressing the expression of E74-like ETS transcription factor 1 (Elf-1). A mechanistic study revealed that EGCG suppressed Elf-1 expression via protein phosphatase 2A/cyclic GMP (cGMP)-dependent mechanisms. We also confirmed that orally administered EGCG and a cGMP inducer upregulated Toll interacting protein expression, increased intracellular levels of cGMP in macrophages, and suppressed Elf-1 expression. These data support EGCG and a cGMP inducer as potential candidate suppressors of TLR4 signaling.

Hydrogen sulphide donors selectively potentiate a green tea polyphenol EGCG-induced apoptosis of multiple myeloma cells

Hydrogen sulphide (H₂S) is a colourless gas with the odour of rotten eggs and has recently been recognized as a signal mediator in physiological activities related with the regulation of homeostasis, the vascular system and the inflammatory system. Here we show that H₂S donors, including sodium hydrogen sulphide (NaHS), GYY 4137 and diallyltrisulfide (DATS), synergistically enhanced the anti-cancer effect of a green tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG) against multiple myeloma cells without affecting normal cells. NaHS significantly potentiated the anti-cancer effect of EGCG and prolonged survival in a mouse xenograft model. In this mechanism, H₂S enhanced apoptotic cell death through cyclic guanosine monophosphate (cGMP)/acid sphingomyelinase pathway induced by EGCG. Moreover, NaHS reduced the enzyme activity of cyclic nucleotide phosphodiesterase that is known as cGMP negative regulator. In conclusion, we identified H₂S as a gasotransmitter that potentiates EGCG-induced cancer cell death.

Arctigenin inhibits triple-negative breast cancers by targeting CIP2A to reactivate protein phosphatase 2A

We have shown that a novel STAT3 inhibitor arctigenin (Atn) induces significant cytotoxicity in triple-negative breast cancer (TNBC) cells. This study further delineated molecular mechanisms where by Atn triggered cytotoxicity in TNBC cells. We found Atn can also inhibit metastasis in TNBC cells through cancerous inhibitor of protein phosphatase 2A (CIP2A) pathway. CIP2A is an endogenous inhibitor of protein phosphatase 2A (PP2A), which can increase the migration and invasion of various cancer cells. PP2A is a tumor suppressor, which is functionally defective in various cancers. Atn-induced metastasis inhibition was associated with reactivation of PP2A, downregulation of CIP2A and Akt phosphorylation. Silencing CIP2A enhanced Atn-induced metastasis inhibition and apoptosis in TNBCs. Furthermore, ectopic expression of CIP2A or inhibition of PP2A in TNBC cells abolished the effects of Atn. In conclusion, we found that enhancement of PP2A activity by inhibition of CIP2A, at least in part, promotes the anti-metastasis effect induced by Atn. Our findings disclose the novel therapeutic mechanism of this targeted agent, and suggest the therapeutic potential and feasibility of developing PP2A enhancers as a novel anticancer strategy.

The Combination of Green Tea Extract and Eriodictyol Inhibited High-Fat/High-Sucrose Diet-Induced Cholesterol Upregulation Is Accompanied by Suppression of Cholesterol Synthesis Enzymes

Western diets induce obesity associated with an increased risk of hypercholesterolaemia. Indeed, obesity-induced hypercholesterolaemia is correlated with increased coronary cardiovascular disease (CVD) risk. Male C57BL/6J mice were fed a normal diet, high-fat and high-sucrose diet (HF/HS), HF/HS with green tea extract powder diet (HF/HS+GT), HF/HS with eriodictyol diet (HF/HS+Eri), or HF/HS with green tea extract powder and eriodictyol diet (HF/HS+GT+Eri) for 8 wk. Body weight was lower in the HF/HS+GT+Eri group than in the HF/HS group (-8.3%, p<0.01). The HF/HS diet elicited an upregulation of total cholesterol levels (-63%, p<0.001), and low-density lipoprotein (LDL) levels (-89%, p<0.001) were significantly suppressed by the GT+Eri diet. Conversely, no change (p>0.05) was observed in the HF/HS+GT and HF/HS+Eri groups. The HF/HS diet-induced hepatic mRNA increase in 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) was ameliorated (-73%) by the oral administration of green tea extract and eriodictyol. Moreover, the GT+Eri diet suppressed HF/HS diet-induced upregulation of 3-hydroxy-3-methylglutaryl-coenzyme A synthase (HMGCS) (-75%, p<0.05). Furthermore, the LDL receptor (LDLR) levels were higher in the HF/HS+GT+Eri group (+50%, p<0.05) than in the HF/HS group. These results suggest that a combination of green tea and eriodictyol decreases cholesterol levels, particularly LDL levels, accompanied by the suppression of HMGCR and HMGCS levels and upregulation of LDLR levels in the liver.

Interplay of myosin phosphatase and protein phosphatase-2A in the regulation of endothelial nitric-oxide synthase phosphorylation and nitric oxide production

The inhibitory phosphorylation of endothelial nitric oxide (NO) synthase (eNOS) at Thr497 (eNOS^pThr497) by protein kinase C or RhoA-activated kinase is a major regulatory determinant of eNOS activity. The signalling mechanisms involved in the dephosphorylation of eNOS^pThr497 have not yet been clarified. This study identifies myosin phosphatase (MP) holoenzyme consisting of protein phosphatase-1 catalytic subunit (PP1c) and MP target subunit-1 (MYPT1) as an eNOS^pThr497 phosphatase. In support of this finding are: (i) eNOS and MYPT1 interacts in various endothelial cells (ECs) and in in vitro binding assays (ii) MYPT1 targets and stimulates PP1c toward eNOS^pThr497 substrate (iii) phosphorylation of MYPT1 at Thr696 (MYPT1^pThr696) controls the activity of MP on eNOS^pThr497. Phosphatase inhibition suppresses both NO production and transendothelial resistance (TER) of ECs. In contrast, epigallocatechin-3-gallate (EGCG) signals ECs via the 67 kDa laminin-receptor (67LR) resulting in protein kinase A dependent activation of protein phosphatase-2A (PP2A). PP2A dephosphorylates MYPT1^pThr696 and thereby stimulates MP activity inducing dephosphorylation of eNOS^pThr497 and the 20 kDa myosin II light chains. Thus an interplay of MP and PP2A is involved in the physiological regulation of EC functions implying that an EGCG dependent activation of these phosphatases leads to enhanced NO production and EC barrier improvement.