Data Source (MLPCN Center Name): The Scripps Research Institute Molecular Screening Center (SRIMSC)
Center Affiliation: The Scripps Research Institute, TSRI
Assay Provider: Benjamin Cravatt, TSRI
Network: Molecular Libraries Probe Production Center Network (MLPCN)
Grant Proposal Number: 1 2 R01 CA087660-05 Fast Track
Grant Proposal PI: Benjamin Cravatt, TSRI
External Assay ID: HEK 293T VIABILITY_INH_LUMI_96_CC50

Name: Late stage results from the probe development effort to identify inhibitors of the protein methylesterase PME-1: Luminescence-based counterscreen assay to identify cytotoxic compounds

Description:

Reversible protein phosphorylation networks play essential roles in most cellular processes. While over 500 kinases catalyze protein phosphorylation, only two enzymes, PP1 and PP2A, are responsible for >90% of all serine/ threonine phosphatase activity (1). Phosphatases, unlike kinases, achieve substrate specificity through complex subunit assembly and post-translational modifications rather than number. PP2A, for example, typically exists as heterotrimer with diverse subunits that may combinatorially make as many as 70 different holoenzyme assemblies (2). Mutations in several of these PP2A subunits have been identified in human cancers, suggesting that PP2A may act as a tumor suppressor (3). Adding further complexity, several residues of the catalytic subunit of PP2A can be reversibly phosphorylated, and the C-terminal leucine residue can be reversibly methylated (4,5). PME-1 is specifically responsible for demethylation of the carboxyl terminus (4).

Methylesterification is thought to control the binding of different subunits to PP2A, but little is known about physiological significance of this post-translational modification in vivo (5). Recently, PME-1 has been identified as a protector of sustained ERK pathway activity in malignant gliomas 6. In order to further elucidate the role of PP2A methylation in vivo, our lab has generated mice that lack PME-1 (PME-1 (-/-) mice) by targeted gene disruption (7). Unfortunately, PME-1 deletion resulted in perinatal lethality, underscoring the importance of PME-1 but hindering our biological studies. Biochemical elucidation of PME-1 would thus greatly benefit from the development of potent and selective chemical inhibitors.

References:

1. Oliver, C. J.; Shenolikar, S., Physiologic importance of protein phosphatase inhibitors. Front. Biosci. 1998, 3, D961-72.
2. Janssens, V.; Goris, J., Protein phosphatase 2A: a highly regulated family of serine/threonine phosphatases implicated in cell growth and signalling. Biochem. J. 2001, 353 (Pt 3), 417-39.
3. Janssens, V.; Goris, J.; Van Hoof, C., PP2A: the expected tumor suppressor. Curr. Opin. Genet. Dev. 2005, 15 (1), 34-41.
4. Lee, J.; Chen, Y.; Tolstykh, T.; Stock, J., A specific protein carboxyl methylesterase that demethylates phosphoprotein phosphatase 2A in bovine brain. Proc. Natl. Acad. Sci. U. S. A. 1996, 93 (12), 6043-7.
5. Wu, J.; Tolstykh, T.; Lee, J.; Boyd, K.; Stock, J. B.; Broach, J. R., Carboxyl methylation of the phosphoprotein phosphatase 2A catalytic subunit promotes its functional association with regulatory subunits in vivo. Embo J. 2000, 19 (21), 5672-81.
6. Puustinen, P.; Junttila, M. R.; Vanhatupa, S.; Sablina, A. A.; Hector, M. E.; Teittinen, K.; Raheem, O.; Ketola, K.; Lin, S.; Kast, J.; Haapasalo, H.; Hahn, W. C.; Westermarck, J., PME-1 protects extracellular signal-regulated kinase pathway activity from protein phosphatase 2A-mediated inactivation in human malignant glioma. Cancer Res. 2009, 69 (7), 2870-7.
7. Ortega-Gutierrez, S.; Leung, D.; Ficarro, S.; Peters, E. C.; Cravatt, B. F., Targeted disruption of the PME-1 gene causes loss of demethylated PP2A and perinatal lethality in mice. PLoS ONE 2008, 3 (7), e2486.

Keywords:

Late stage, PME-1, protein phosphatase methylesterase 1, PPME-1, cancer, inhibitor, HEK 293T cells, cytotoxicity, luminescence, luciferase, viability, secondary assay, 96, Scripps, The Scripps Research Institute Molecular Screening Center, SRIMSC, Molecular Libraries Probe Production Centers Network, MLPCN

Assay Overview:

The purpose of this assay is to determine cytotoxicity of inhibitor compounds. In this assay, HEK cells are incubated with test compounds, followed by determination of cell viability. The assay utilizes the CellTiter-Glo luminescent reagent to measure intracellular ATP in viable cells. Luciferase present in the reagent catalyzes the oxidation of beetle luciferin to oxyluciferin and light in the presence of cellular ATP. Well luminescence is directly proportional to ATP levels and cell viability. As designed, compounds that reduce cell viability will reduce ATP levels, luciferin oxidation and light production, resulting in decreased well luminescence. Compounds were tested in triplicate in a 10-point 1:3 dilution series starting at a nominal test concentration of 40 micromolar.

Protocol Summary:

This assay was started by dispensing 5 x 103 HEK 293T cells/well into a 96-well plate. Compound (0.001-100 mM) or DMSO was added to each well, and after 48h cell viability was determined by the CellTitre assay (Promega).

PubChem Activity Score:

In this assay the PubChem Activity Score is assigned a value of 100 for probe compounds, 50 for nontoxic compounds, and 0 for toxic compounds.

PubChem Activity Outcome:

Compounds with a cytotoxic concentration (CC)50 > 50 micromolar are considered nontoxic, and compounds with a CC50 = 50 micromolar are considered toxic.

List of Reagents:

HEK cells (provided by Assay Provider)
Cell Titer-Glo (Promega, part G75729)
96-well plates

This assay was performed in the laboratory of the Assay Provider with compounds ordered as powders. Probes were identified for this project. Details of protocols, compound structures, and results from the original assays can be found in PubChem at the respective AIDs listed in the Related Bioassays section. Please also see Summary AID 1790. The results of our probe development efforts can be found at http://mlpcn.florida.scripps.edu/index.php/probes/probe-reports.html. One paper has been published detailing the emetine probe (7).

Grant Number: 1 2 R01 CA087660-05