Tautomycin: an inhibitor of protein phosphatases 1 and 2A but not a tumor promoter on mouse skin and in rat glandular stomach

Epoxide-Based Synthetic Approaches toward Polypropionates and Related Bioactive Natural Products

Polypropionate units are a common structural feature of many of the natural products in polyketides, some of which have shown a broad range of antimicrobial and therapeutic potential. Polypropionates are composed of a carbon skeleton with alternating methyl and hydroxy groups with a specific configuration. Different approaches have been developed for the synthesis of polypropionates and herein we include, for the first time, all of the epoxide-based methodologies that have been reported over the years by several research groups such as Kishi, Katsuki, Marashall, Miyashita, Prieto, Sarabia, Jung, McDonald, etc. Several syntheses of polypropionate fragments and natural products that employed epoxides as key intermediates have been described and summarized in this review. These synthetic approaches involve enatio- and diastereoselective synthesis of epoxides (epoxy-alcohols, epoxy-amides, and epoxy-esters) and their regioselective cleavage with carbon and/or hydride nucleophiles. In addition, we included a description of the isolation and biological activities of the polypropionates and related natural products that have been synthetized using epoxide-based approaches. In conclusion, the epoxide-based methodologies are a non-aldol alternative approach for the construction of polypropionate.

A comprehensive overview of PPM1B: From biological functions to diseases

Reversible phosphorylation of proteins is an important mechanism that regulates cellular processes, which are precisely regulated by protein kinases and phosphatases. PPM1B is a metal ion-dependent serine/threonine protein phosphatase, which regulates multiple biological functions by targeting substrate dephosphorylation, such as cell cycle, energy metabolism, inflammatory responses. In this review, we summarized the occurrent understandings of PPM1B focused on its regulation of signaling pathways, related diseases, and small-molecular inhibitors, which may provide new insights for the identification of PPM1B inhibitors and the treatment of PPM1B-related diseases.

A superfolding Spinach2 reveals the dynamic nature of trinucleotide repeat-containing RNA

Imaging RNA in living cells is a challenging problem in cell biology. One strategy for genetically encoding fluorescent RNAs is to express them as fusions with Spinach, an 'RNA mimic of GFP'. We found that Spinach was dimmer than expected when used to tag constructs in living cells owing to a combination of thermal instability and a propensity for misfolding. Using systematic mutagenesis, we generated Spinach2 that overcomes these issues and can be used to image diverse RNAs. Using Spinach2, we detailed the dynamics of the CGG trinucleotide repeat-containing 'toxic RNA' associated with Fragile X-associated tremor/ataxia syndrome, and show that these RNAs form nuclear foci with unexpected morphological plasticity that is regulated by the cell cycle and by small molecules. Together, these data demonstrate that Spinach2 exhibits improved versatility for fluorescently labeling RNAs in living cells.

Is protein phosphatase inhibition responsible for the toxic effects of okadaic Acid in animals?

Okadaic acid (OA) and its derivatives, which are produced by dinoflagellates of the genera Prorocentrum and Dinophysis, are responsible for diarrhetic shellfish poisoning in humans. In laboratory animals, these toxins cause epithelial damage and fluid accumulation in the gastrointestinal tract, and at high doses, they cause death. These substances have also been shown to be tumour promoters, and when injected into the brains of rodents, OA induces neuronal damage reminiscent of that seen in Alzheimer’s disease. OA and certain of its derivatives are potent inhibitors of protein phosphatases, which play many roles in cellular metabolism. In 1990, it was suggested that inhibition of these enzymes was responsible for the diarrhetic effect of these toxins. It is now repeatedly stated in the literature that protein phosphatase inhibition is not only responsible for the intestinal effects of OA and derivatives, but also for their acute toxic effects, their tumour promoting activity and their neuronal toxicity. In the present review, the evidence for the involvement of protein phosphatase inhibition in the induction of the toxic effects of OA and its derivatives is examined, with the conclusion that the mechanism of toxicity of these substances requires re-evaluation.

Okadaic acid promotes angiogenesis via activation of hypoxia-inducible factor-1

Okadaic acid, a potent tumor promoter and an inhibitor of protein phosphatase 1 and 2A, has also been characterized as an angiogenic inducer in the chorioallantoic membrane of the chick embryo. To elucidate the roles of okadaic acid on angiogenic processes, we conducted in vitro angiogenesis assays. In this study, we report that okadaic acid potently stimulated tube formation, migration, and invasion of human umbilical vein endothelial cells. Moreover, okadaic acid elevated the activities of hypoxia-inducible factor-1 (HIF-1), which is closely related with the expression of vascular endothelial growth factor. Exposure to okadaic acid markedly increased the HIF-1alpha protein level through up-regulation of translation via activation of Akt and mTOR pathway. Taken together, these results demonstrated that okadaic acid promotes angiogenesis through stimulation of Akt mediated HIF-1alpha translation.

Okadaic acid protects human neuroblastoma SH-SY5Y cells from 1-methyl-4-phenylpyridinium ion-induced apoptosis

1-methyl-4-phenylpyridinium ion (MPP(+)) has been shown to selectively inhibit mitochondrial function and induce a parkinsonism-like syndrome. MPP(+) stimulates the production of reactive oxygen species (ROS) and induces cell death in vitro. In this study, we investigated the protective effects of okadaic acid on MPP(+)-induced cell death in SH-SY5Y neuroblastoma cells. We found that MPP(+)-induced apoptosis and -ROS generation were blocked by okadaic acid. MPP(+)-mediated activation of AKT was also inhibited by okadaic acid. Taken together, these results demonstrate that okadaic acid protects against MPP(+)-induced apoptosis by blocking ROS stimulation and ROS-mediated signaling pathways in SH-SY5Y cells. These data indicated that okadaic acid could provide a therapeutic strategy for the treatment of neurodegenerative diseases including Parkinson's disease.

Okadaic acid stimulates the expression of vascular endothelial growth factor gene

Vascular endothelial growth factor (VEGF) is a specific mitogen for vascular endothelial cells and has been implicated in tumor angiogenesis. Okadaic acid, an inhibitor of protein phosphatases 1 and 2A, is a non-12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoter in two-stage carcinogenesis experiments in mouse skin. To elucidate the role of VEGF in the angiogenesis of these experimental tumors, the effect of okadaic acid on VEGF gene expression was examined. In NIH 3T3, Rat1, HeLa, and A431 cells, VEGF mRNA was upregulated by 5- to 10-fold after incubation with okadaic acid. Furthermore, the amount of VEGF protein in the culture medium was significantly increased after stimulation with okadaic acid. Interestingly, okadaic acid-induced upregulation of VEGF mRNA was not suppressed by protein kinase C (PKC) inhibitor or by tumor necrosis factor alpha blocking antibody, although TPA-induced VEGF upregulation was strongly suppressed by PKC inhibitor. Our results indicate that okadaic acid is a new and potent inducer of VEGF, suggesting the involvement of VEGF as an angiogenic factor during multistep carcinogenesis in vivo.

Mechanistic aspects of green tea as a cancer preventive: effect of components on human stomach cancer cell lines

It is now well accepted that (-)-epigallocatechin gallate (EGCG) inhibits carcinogenesis in the digestive tract in rodents. To understand the mechanisms of anticarcinogenesis, we first studied growth inhibition by EGCG in human stomach cancer cell lines established at Seoul National University (SNU cell lines). Inhibition by EGCG of [3H]thymidine incorporation into eight SNU cell lines was examined, in relation to transforming growth factor-beta (TGF-beta) responsiveness. Various tea polyphenols derived from green tea and black tea induced growth inhibition and apoptosis of human stomach cancer cell line KATO III, and inhibition of tumor necrosis factor-alpha (TNF-alpha) release from the cells, in the order of (-)-epicatechin gallate (ECG), EGCG, (-)-epigallocatechin (EGC), teaflavins (TF) and (-)-epicatechin (EC). In addition, we demonstrated that EGCG inhibited TNF-alpha gene expression in KATO III cells, as well as okadaic acid-induced AP-1 and NF-kappa B activation. The inhibitory potencies of EGCG for AP-1 and NF-kappa B binding to DNA were different between KATO III cells and mouse fibroblast cell line BALB/3T3. Thus, EGCG and other tea polyphenols may interact with various transcription factors, in addition to AP-1 and NF-kappa B, in nuclei of various cells, resulting in inhibition of TNF-alpha gene expression and TNF-alpha release.

Different moieties of tautomycin involved in protein phosphatase inhibition and induction of apoptosis

The effects of tautomycin and its derivatives on protein phosphatases PP1 and PP2A and their apoptosis-inducing activity toward human leukemia Jurkat cells were examined, and the relationship between chemical structure and function was discussed. Among the compounds we examined, tautomycin was the most potent inhibitor and the most effective inducer of apoptosis. It inhibited PP1 and PP2A enzymatic activity concentration-dependently with IC50 values of 20 and 75 pM, respectively, in the presence of 0.01% Brij-35, and an LC50 value of 1 microM. Esterification of the anhydride moiety of tautomycin markedly increased the IC50 for the protein phosphatases. The C1'-C7' fragment of tautomycin had no inhibitory effect, but the fragment containing the C22-C26 moiety was inhibitory. These results suggest that the C22-C26 moiety is essential for inhibition of protein phosphatase activity and that the anhydride moiety enhances the inhibition. However, the esterification of the anhydride did not decrease, nor did the inclusion of the C22-C26 moiety increase the apoptosis-inducing activity. On the other hand, the C1-C18 moiety of tautomycin was essential for induction of apoptosis, and the conformation and the arrangement of functionalities of the C18-C26 carbon chain affected the apoptosis activity. However, modification of C1-C18, C1-C21, or C1-C26 compounds had little effect on phosphatase inhibitory activity. Our results strongly suggest that different moieties of tautomycin are involved in protein phosphatase inhibition and induction of apoptosis.