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: PME-1_INH_FP_GEL_%INH

Name: Late stage results from the probe development effort to identify inhibitors of the protein methylesterase PME-1: Gel-based Activity-Based Protein Profiling (ABPP) Inhibition

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, Probes, PME-1, protein phosphatase methylesterase 1, PPME-1, cancer, fluorescence, fluorophosphonate rhodamine, FP-Rh, inhibitor, confirmation, gel-based ABPP, Scripps, Scripps Research Institute Molecular Screening Center, SRIMSC, Molecular Libraries Probe Production Centers Network, MLPCN.

Assay Overview:

The purpose of this assay is to confirm activity of compounds identified as active in the uHTS primary (AID 2130) and confirmation screens (AID 2171). In this assay, a fluorophosphonate-rhodamine (FP-Rh) probe which broadly targets enzymes from the serine hydrolase family is used to label PME-1 in mouse brain soluble lysates in the presence of test compounds. The reaction products are separated by SDS-PAGE and visualized in-gel using a flatbed fluorescence scanner. The percentage activity remaining is determined by measuring the integrated optical density of the bands. As designed, test compounds that act as PME-1 inhibitors will prevent PME-1-probe interactions, giving lower fluorescence intensity in the band in the gel. Percent inhibition of endogenously expressed PME-1 (compound at 20 uM) was determined.

Protocol Summary:

A preparation of mouse brain cytosol (2mg/mL) was incubated with DMSO or compound (20 mM) for 30 min at 25 degrees Celsius before the addition of FP-rhodamine at a final concentration of 75 nM in 50 ul total reaction volume. The reaction was incubated for 45 min at 25 degrees Celsius, quenched with 2x SDS-PAGE loading buffer, boiled for 5 min at 90 degrees Celsius, separated by SDS-PAGE and visualized in-gel. The percentage activity remaining was determined by measuring the integrated optical density of the bands.

PubChem Activity Score:

The reported PubChem Activity Score has been normalized to 100% observed primary inhibition. The range for active compounds is 100-77, for inactive 66-0.

List of Reagents:

Mouse brain cytosol (provided by Assay Provider)
FP-rhodamine (provided by Assay Provider)
Sodium Chloride (Fisher, part 980597)
1M Tris, pH 8.0 (Invitrogen, part T-3038)

This assay was performed in the laboratory of the Assay Provider with compounds ordered as powders. Details of protocols, compound structures, and results from the original assays can be found in PubChem at the respective AIDs listed below. The results of our probe development efforts can be found at http://mlpcn.florida.scripps.edu/index.php/probes/probe-reports.html.

Grant Number: 1 2 R01 CA087660-05