Dataset Information

Structure-activity relationship studies of fostriecin, cytostatin, and key analogs, with PP1, PP2A, PP5, and( beta12-beta13)-chimeras (PP1/PP2A and PP5/PP2A), provide further insight into the inhibitory actions of fostriecin family inhibitors.

ABSTRACT: Fostriecin and cytostatin are structurally related natural inhibitors of serine/threonine phosphatases, with promising antitumor activity. The total synthesis of these antitumor agents has enabled the production of structural analogs, which are useful to explore the biological significance of features contained in the parent compounds. Here, the inhibitory activity of fostriecin, cytostatin, and 10 key structural analogs were tested in side-by-side phosphatase assays to further characterize their inhibitory activity against PP1c (Ser/Thr protein phosphatase 1 catalytic subunit), PP2Ac (Ser/Thr protein phosphatase 2A catalytic subunit), PP5c (Ser/Thr protein phosphatase 5 catalytic subunit), and chimeras of PP1 (Ser/Thr protein phosphatase 1) and PP5 (Ser/Thr protein phosphatase 5), in which key residues predicted for inhibitor contact with PP2A (Ser/Thr protein phosphatase 2A) were introduced into PP1 and PP5 using site-directed mutagenesis. The data confirm the importance of the C9-phosphate and C11-alcohol for general inhibition and further demonstrate the importance of a predicted C3 interaction with a unique cysteine (Cys(269)) in the beta12-beta13 loop of PP2A. The data also indicate that additional features beyond the unsaturated lactone contribute to inhibitory potency and selectivity. Notably, a derivative of fostriecin lacking the entire lactone subunit demonstrated marked potency and selectivity for PP2A, while having substantially reduced and similar activity against PP1 and PP1/PP2A- PP5/PP2A-chimeras that have greatly increased sensitivity to both fostriecin and cytostatin. This suggests that other features [e.g., the (Z,Z,E)-triene] also contribute to inhibitory selectivity. When considered together with previous data, these studies suggest that, despite the high structural conservation of the catalytic site in PP1, PP2A and PP5, the development of highly selective catalytic inhibitors should be feasible.

SUBMITTER: Swingle MR

PROVIDER: S-EPMC2766224 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature

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Structure-activity relationship studies of fostriecin, cytostatin, and key analogs, with PP1, PP2A, PP5, and( beta12-beta13)-chimeras (PP1/PP2A and PP5/PP2A), provide further insight into the inhibitory actions of fostriecin family inhibitors.

Swingle Mark R MR Amable Lauren L Lawhorn Brian G BG Buck Suzanne B SB Burke Christopher P CP Ratti Pukar P Fischer Kimberly L KL Boger Dale L DL Honkanen Richard E RE

The Journal of pharmacology and experimental therapeutics 20090710 1

Fostriecin and cytostatin are structurally related natural inhibitors of serine/threonine phosphatases, with promising antitumor activity. The total synthesis of these antitumor agents has enabled the production of structural analogs, which are useful to explore the biological significance of features contained in the parent compounds. Here, the inhibitory activity of fostriecin, cytostatin, and 10 key structural analogs were tested in side-by-side phosphatase assays to further characterize thei ...[more]

PMID: 19592665

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Project description:The protein phosphatases PP2A and PP1 are major regulators of a variety of cellular processes in yeast and other eukaryotes. Here, we reveal that both enzymes are direct targets of glucose sensing. Addition of glucose to glucose-deprived yeast cells triggered rapid posttranslational activation of both PP2A and PP1. Glucose activation of PP2A is controlled by regulatory subunits Rts1, Cdc55, Rrd1 and Rrd2. It is associated with rapid carboxymethylation of the catalytic subunits, which is necessary but not sufficient for activation. Glucose activation of PP1 was fully dependent on regulatory subunits Reg1 and Shp1. Absence of Gac1, Glc8, Reg2 or Red1 partially reduced activation while Pig1 and Pig2 inhibited activation. Full activation of PP2A and PP1 was also dependent on subunits classically considered to belong to the other phosphatase. PP2A activation was dependent on PP1 subunits Reg1 and Shp1 while PP1 activation was dependent on PP2A subunit Rts1. Rts1 interacted with both Pph21 and Glc7 under different conditions and these interactions were Reg1 dependent. Reg1-Glc7 interaction is responsible for PP1 involvement in the main glucose repression pathway and we show that deletion of Shp1 also causes strong derepression of the invertase gene SUC2. Deletion of the PP2A subunits Pph21 and Pph22, Rrd1 and Rrd2, specifically enhanced the derepression level of SUC2, indicating that PP2A counteracts SUC2 derepression. Interestingly, the effect of the regulatory subunit Rts1 was consistent with its role as a subunit of both PP2A and PP1, affecting derepression and repression of SUC2, respectively. We also show that abolished phosphatase activation, except by reg1?, does not completely block Snf1 dephosphorylation after addition of glucose. Finally, we show that glucose activation of the cAMP-PKA (protein kinase A) pathway is required for glucose activation of both PP2A and PP1. Our results provide novel insight into the complex regulatory role of these two major protein phosphatases in glucose regulation.

Project description:Here we report that ALDH1L1 (FDH, a folate enzyme with tumor suppressor-like properties) inhibits cell motility. The underlying mechanism involves F-actin stabilization, re-distribution of cytoplasmic actin toward strong preponderance of filamentous actin and formation of actin stress fibers. A549 cells expressing FDH showed a much slower recovery of green fluorescent protein-actin fluorescence in a fluorescence recovery after photobleaching assay, as well as an increase in G-actin polymerization and a decrease in F-actin depolymerization rates in pyren-actin fluorescence assays indicating the inhibition of actin dynamics. These effects were associated with robust dephosphorylation of the actin depolymerizing factor cofilin by PP1 and PP2A serine/threonine protein phosphatases, but not the cofilin-specific phosphatases slingshot and chronophin. In fact, the PP1/PP2A inhibitor calyculin prevented cofilin dephosphorylation and restored motility. Inhibition of FDH-induced apoptosis by the Jun N-terminal kinase inhibitor SP600125 or the pan-caspase inhibitor zVAD-fmk did not restore motility or levels of phosphor-cofilin, indicating that the observed effects are independent of FDH function in apoptosis. Interestingly, cofilin small interfering RNA or expression of phosphorylation-deficient S3A cofilin mutant resulted in a decrease of G-actin and the actin stress fiber formation, the effects seen upon FDH expression. In contrast, the expression of S3D mutant, mimicking constitutive phosphorylation, prevented these effects further supporting the cofilin-dependent mechanism. Dephosphorylation of cofilin and inhibition of motility in response to FDH can also be prevented by the increased folate in media. Furthermore, folate depletion itself, in the absence of FDH, resulted in cofilin dephosphorylation and inhibition of motility in several cell lines. Our experiments showed that these effects were folate specific and not a general response to nutrient starvation. Overall, this study shows the presence of distinct intracellular signaling pathways regulating motility in response to folate status and points toward mechanisms involving folates in promoting a malignant phenotype.

Dataset Information

Structure-activity relationship studies of fostriecin, cytostatin, and key analogs, with PP1, PP2A, PP5, and( beta12-beta13)-chimeras (PP1/PP2A and PP5/PP2A), provide further insight into the inhibitory actions of fostriecin family inhibitors.

Publications

Structure-activity relationship studies of fostriecin, cytostatin, and key analogs, with PP1, PP2A, PP5, and( beta12-beta13)-chimeras (PP1/PP2A and PP5/PP2A), provide further insight into the inhibitory actions of fostriecin family inhibitors.

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