Late stage assay provider results from the probe development effort to identify inhibitors of Protein Phosphatase Methylesterase 1 (PME-1): luminescence-based biochemical dose response assay to determine cytotoxicity of inhibitor compounds
Late stage assay provider results from the probe development effort to identify inhibitors of PME-1: fluorescence-based dose response cell-based gel-based competitive Activity-Based Protein Profiling (ABPP) ABHD10 selectivity assay
Late stage assay provider results from the probe development effort to identify inhibitors of PME-1: fluorescence-based biochemical gel-based competitive Activity-Based Protein Profiling (ABPP) inhibition and selectivity among cysteine-reactive proteins
Late stage assay provider results from the probe development effort to identify inhibitors of PME-1: fluorescence-based cell-based gel-based competitive Activity-Based Protein Profiling (ABPP) inhibition of ABHD10 in vivo
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 Centers Network (MLPCN) Grant Proposal Number: 1 R01 CA132630-01 Grant Proposal PI: Benjamin Cravatt, TSRI External Assay ID: PME1_INH_LCMS_ABPP-SILAC
Name: Late stage assay provider results from the probe development effort to identify inhibitors of PME-1: LC-MS/MS-based cell-based ABPP-SILAC assay.
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 (6).
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 (7). Recently, PME-1 has been identified as a protector of sustained ERK pathway activity in malignant gliomas (8). 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 (9). 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.
1. Oliver, C. J., Shenolikar, S. (1998). Physiologic importance of protein phosphatase inhibitors. Front. Biosci. 3, D961-972. 2. Janssens, V., Goris, J. (2001). Protein phosphatase 2A: a highly regulated family of serine/threonine phosphatases implicated in cell growth and signalling. Biochem. J. 353, 417-439. 3. Janssens, V., Goris, J., Van Hoof, C. (2005). PP2A: the expected tumor suppressor. Curr. Opin. Genet. Dev. 15, 34-41. 4. Chen, J., Martin, B. L., Brautigan, D. L. (1992). Regulation of protein serine-threonine phosphatase type-2A by tyrosine phosphorylation. Science 257, 1261-1264. 5. Favre, B., Zolnierowicz, S., Turowski, P., Hemmings, B. A. (1994). The catalytic subunit of protein phosphatase 2A is carboxyl-methylated in vivo. J. Biol. Chem. 269, 16311-16317. 6. Lee, J., Chen, Y., Tolstykh, T., Stock, J. (1996). A specific protein carboxyl methylesterase that demethylates phosphoprotein phosphatase 2A in bovine brain. Proc. Natl. Acad. Sci. U. S. A. 93, 6043-6047. . 7. Wu, J., Tolstykh, T., Lee, J., Boyd, K., Stock, J. B., Broach, J. R. (2000). Carboxyl methylation of the phosphoprotein phosphatase 2A catalytic subunit promotes its functional association with regulatory subunits in vivo. Embo J. 19, 5672-5681. 8. 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. (2009). PME-1 protects extracellular signal-regulated kinase pathway activity from protein phosphatase 2A-mediated inactivation in human malignant glioma. Cancer Res. 69, 2870-2877. 9. Ortega-Gutierrez, S., Leung, D., Ficarro, S., Peters, E. C., Cravatt, B. F. (2008). Targeted disruption of the PME-1 gene causes loss of demethylated PP2A and perinatal lethality in mice. PLoS ONE 3, e2486.
late stage, late stage AID, assay provider, powders, PME-1, protein phosphatase methylesterase 1, PPME-1, protein phosphatase 2a, PP2A, methylation, demethylation, counterscreen, liquid chromatography, LC, tandem mass spectrometry, MS/MS, activity-based protein profiling, ABPP, stable isotope labeling with amino acids in cell culture, SILAC, ABPP-SILAC, fluorophosphonate biotin, FP-Rh, inhibitor, selectivity, anti-targets, Scripps, Scripps Research Institute Molecular Screening Center, SRIMSC, Molecular Libraries Probe Production Centers Network, MLPCN
The purpose of this assay is to determine the selectivity profile of powder samples of test compounds using activity-based protein profiling (ABPP) in combination with stable isotope labeling with amino acids in cell culture (SILAC). In this assay, cultured Neuro-2A cells are metabolically labeled with light or heavy amino acids. Light and heavy cells are treated with test compound and DMSO, respectively, in situ. Cells are lysed, proteomes are treated with the serine-hydrolase-specific activity-based fluorophosphonate-biotin (FP-biotin) affinity probe, and combined in a 1:1 (w/w) ratio. Biotinylated proteins are enriched, trypsinized, and analyzed by multi-dimensional liquid chromatography tandem mass spectrometery LC/LC-MS/MS (MudPIT). Inhibition of target and anti-target activity is quantified by comparing intensities of light and heavy peptide peaks. As designed, compounds that act as inhibitors will block FP-biotin labeling, reducing enrichment in the inhibitor-treated (light) sample relative to the DMSO-treated (heavy) sample, resulting in a smaller light/heavy ratio for each protein. Proteins not targeted by inhibitors would be expected to have a ratio of 1.
Stable isotope labeling with amino acids in cell culture (SILAC). Neuro-2A murine neuroblastoma cells were initially grown for 10 passages in either light or heavy SILAC DMEM medium supplemented with 10% dialyzed FCS and 2 mM L-glutamine. Light media was supplemented with 100 ug/mL L-arginine and 100 ug/mL L-lysine. Heavy media was supplemented with 100 ug/mL [13C615N4]-L-Arginine and 100 ug/mL [13C615N2]-L-Lysine. Light cells (in 10 mL media) were treated with 100 nM test compound (75 uL of a 200x stock in DMSO) and heavy cells were treated with DMSO (75 uL) for 2 hours at 37 C. Cells were washed 2 times with DPBS, harvested, and homogenized by sonication in DPBS (1mL). The soluble and membrane fractions were isolated by centrifugation (100K x g, 45 minutes) and the protein concentration was adjusted to 2 mg/mL with DPBS in each fraction.
Sample preparation for ABPP-SILAC. The light and heavy proteomes were labeled with 10 uM of FP-biotin (500 uL total reaction volume) for 2 hours at 25 C. After incubation, light and heavy proteomes were mixed in 1:1 ratio, and the membrane proteomes were additionally solubilized with 1% Triton-X100. The proteomes were desalted over PD-10 desalting columns (GE Healthcare) and FP-labeled proteins were enriched with streptavidin beads. The beads were washed with 1% SDS in DPBS (1x), 6M urea (1x), and DPBS (2x), then resuspended in 6 M urea, reduced with 5 mM TCEP for 20 minutes, and alkylated with 10 mM iodoacetamide for 30 minutes at 25 C in the dark. On-bead digestions were performed for 12 hours at 37 C with sequence-grade modified trypsin (Promega; 2 ug) in 2M urea in the presence of 2 mM CaCl2. Peptide samples were acidified to a final concentration of 5% (v/v) formic acid, pressure-loaded on to a biphasic (strong cation exchange/reversed phase) capillary column and analyzed as described below.
LC-MS/MS analysis. Digested and acidified peptide mixtures were analyzed by two-dimensional liquid chromatography (2D-LC) separation in combination with tandem mass spectrometry using an Agilent 1200-series quaternary pump and Thermo Scientific LTQ-Orbitrap Velos ion trap mass spectrometer. Peptides were eluted in a 5-step MudPIT experiment using 0%, 25%, 50%, 80%, and 100% salt bumps of 500 mM aqueous ammonium acetate and data were collected in data-dependent acquisition mode with dynamic exclusion turned on (20 s, repeat of 1). Specifically, one full MS (MS1) scan (400-1800 m/z) was followed by 30 MS2 scans of the most abundant ions. The MS2 spectra data were extracted from the raw file using RAW Xtractor (version 220.127.116.11; publicly available at http://fields.scripps.edu/downloads.php). MS2 spectra data were searched using the ProLuCID algorithm (publicly available at http://fields.scripps.edu/downloads.php) against the latest version of the mouse IPI database concatenated with the reversed database for assessment of false-discovery rates. ProLucid searches allowed for static modification of cysteine residues (+57.02146 due to alkylation), methionine oxidation (+15.9949), mass shifts of labeled amino acids (+10.0083 R, 8.0142 K) and no enzyme specificity. The resulting MS2 spectra matches were assembled into protein identifications and filtered using DTASelect (version 2.0) using the --modstat, --mass, and --trypstat options (applies different statistical models for the analysis of high resolution masses, peptide digestion state, and methionine oxidation state respectively). Ratios of Light/Heavy peaks were calculated using in-house software and normalized at the peptide level to the average ratio of all non-serine hydrolase peptides. Reported ratios represent the mean of all unique, quantified peptides per protein and do not include peptides that were greater than 3 standard deviations from the median peptide value. Proteins with less than three peptides per protein ID were not included in the analysis.
Ratio = Average( AUC_light / AUC_heavy ) calculated for all unique peptides
AUC_light is the area-under-the-curve for the light peptide pair from cells treated with test compound. AUC_heavy is the area-under-the-curve for the heavy peptide pair from cells treated with DMSO.
PubChem Activity Outcome and Score:
The following applies to each panel:
A compound with a light/heavy ratio of less than or equal to 0.5 for a particular target/anti-target was considered "active". A compound with a light/heavy ratio of greater than 0.5 for a specified target/anti-target was considered "inactive".
Overall Outcome and Score:
A compound was considered active if it was active for PME1 and inactive for all anti-target serine hydrolases tested.
The PubChem Activity Score is assigned a value of 100 for active compounds, and 0 for inactive compounds.
The PubChem Activity Score range for active compounds is 100-100. There are no inactive compounds.