Kevin Hsiao

Apoptotic cells, at all stages of the death process, trigger characteristic signaling events that are divergent from and dominant over those triggered by necrotic cells: Implications for the delayed clearance model of autoimmunity

Current models of autoimmunity suggest that delayed clearance of apoptotic cells leads to the presentation of apoptotic antigens in the context of inflammatory signals, with resultant autoimmunity. These models implicitly assume that, in contrast to early apoptotic cells (that retain membrane integrity), late apoptotic cells (with compromised membranes) act like necrotic cells (which also lack intact membranes), possibly because of the release of proinflammatory intracellular contents. We showed previously that early apoptotic and necrotic cells induce distinct mitogen-activated protein kinase modules in macrophages with which they interact. Exposure to apoptotic cells led to nearly complete inhibition of both basal and macrophage colony-stimulating factor-induced ERK1/2 by macrophages. In contrast, necrotic cells induced ERK1/2. We show here that apoptotic cells also strongly induced both c-Jun N-terminal kinase and p38, whereas necrotic cells had no detectable effect on c-Jun N-terminal kinase and p38. We also compared the signaling events induced in macrophages by exposure to early apoptotic cells, late apoptotic cells, and necrotic cells. The signaling events induced by late apoptotic cells were identical to and just as potent as those induced by early apoptotic cells. Thus, apoptotic cells are functionally equivalent throughout the cell death process, irrespective of membrane integrity. Moreover, the effects of both early and late apoptotic cells on signaling were dominant over those of necrotic cells. These data show that apoptotic cells do not become proinflammatory upon the loss of membrane integrity and are inconsistent with the notion that delayed clearance alone can lead to autoimmunity.

A Homogeneous, Nonradioactive High-Throughput Fluorogenic Protein Phosphatase Assay

Protein phosphatases are critical components in cellular regulation; they do not only act as antioncogenes by antagonizing protein kinases, but they also play a positive regulatory role in a variety of cellular processes that require dephosphorylation. Thus, assessing the function of these enzymes necessitates the need for a robust, sensitive assay that accurately measures their activities. The authors present a novel, homogeneous, and nonradioactive assay to measure the enzyme activity of low concentrations of several protein phosphatases (phosphoserine/phosphothreonine phosphatases and phosphotyrosine phosphatases). The assay is based on the use of fluorogenic peptide substrates (rhodamine 110, bis-phosphopeptide amide) that do not fluoresce in their conjugated form, which is resistant to cleavage by aminopeptidases. However, upon dephosphorylation by the phosphatase of interest, the peptides become cleavable by the protease and release the highly fluorescent-free rhodamine 110. The assay is rapid, can be completed in less than 2 h, and can be carried out in multiwell plate formats such as 96-, 384-, and 1536-well plates. The assay has an excellent dynamic range, high signal-to-noise ratio, and a Z′ of more than 0.8, and it is easily adapted to a robotic system for drug discovery programs targeting protein phosphatases.

A bioluminescent assay for monitoring conjugation of ubiquitin and ubiquitin-like proteins

Post-translational modification of target proteins by ubiquitin (Ub) and ubiquitin-like (Ubl) proteins is a critical mechanism for regulating protein functions affecting diverse cellular processes. Ub/Ubl proteins are conjugated to lysine residues in substrate proteins through an adenosine triphosphate (ATP)-dependent enzymatic cascade involving enzyme 1 (E1)-activating enzyme, E2-conjugating enzyme, and E3 ligase. The amount of adenosine monophosphate (AMP) produced in the first step, involving E1-mediated Ub/Ubl activation, represents an accurate measure of Ub/Ubl transfer during the process. Here we describe a novel bioluminescent assay platform, AMP-Glo, to quantify Ub/Ubl conjugation by measuring the AMP generated. The AMP-Glo assay is performed in a two-step reaction. The first step terminates the ubiquitination reaction, depletes the remaining ATP, and converts the AMP generated in the ubiquitination reaction to adenosine diphosphate (ADP), and in the second step the ADP generated is converted to ATP, which is detected as a bioluminescent signal using luciferase/luciferin, proportional to the AMP concentration and correlated with the Ub/Ubl transfer activity. We demonstrate the use of the assay to study Ub/Ubl conjugation and screen for chemical modulators of enzymes involved in the process. Because there is a sequential enhancement in light output in the presence of E1, E2, and E3, the AMP-Glo system can be used to deconvolute inhibitor specificity.

A Homogenous Bioluminescent System for Measuring GTPase, GTPase Activating Protein, and Guanine Nucleotide Exchange Factor Activities

Abstract GTPases play a major role in various cellular functions such as cell signaling, cell proliferation, cell differentiation, cytoskeleton modulation, and cell motility. Deregulation or mutation of these proteins has considerable consequences resulting in multiple pathological conditions. Targeting GTPases and its regulators has been challenging due to paucity of convenient assays. In this study, we describe a homogenous bioluminescent assay for monitoring the activities of GTPase and its immediate regulators: GTPase activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs). Since Mg2+ plays a critical role in influencing the affinity of GTPases with guanosine triphosphate/guanosine diphosphate (GTP/GDP) and the process of nucleotide exchange, manipulating Mg2+ concentrations in the GTPase reaction buffer allows continuous progression of the GTPase cycle and faster hydrolysis of GTP. The assay relies on enzymatic conversion of GTP that remains after the GTPase reaction to ATP and detection of the generated ATP using the luciferin/luciferase combination. The GTPase/GAP/GEF-Glo assay system enables monitoring of GTPase, GAP-stimulated GTPase, GAP, and GEF activities. The system can also be used to analyze these proteins when expressed in cells as fusion proteins by performing the assay in a pulldown format. The assays showed minimal false hits upon testing for compound interference using the library of pharmacologically active compounds and its robustness was demonstrated by a high Z′-factor of 0.93 and CV of 2.2%. The assay system has a high dynamic range, formatted in a convenient add–mix–read, and applicable to high-throughput screening.

Abstract 164: High throughput homogenous bioluminescent assays for monitoring the concentrations of AMP, ADP and ATP

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Adenine nucleotides are major determinants of the energy status of the cell and thus any modulation of their cellular concentration has significant consequences to cellular metabolism, cellular growth and cell death. ATP generating enzymes are usually involved in anabolic processes while ATP consuming enzymes are involved in catabolite processes. We have developed biochemical assays that monitor the concentrations of ATP, ADP and AMP in a biochemical reaction. For instance ATP depletion dependent assays and ADP generating assays monitor the activity of kinases and ATPases. These universal assays can measure the activity of various enzymes with no modification of the native substrate and the ability to use diverse substrates such as proteins, peptides, lipids, sugars, etc. The AMP generating reactions such as ubiquitin ligases, aa aminoacyl t-RNA synthetases, DNA ligases, cAMP-dependent phosphodiesterases, etc. can be also monitored with high sensitivity and reproducibility. We will show data using these various technologies in monitoring the various adenine nucleotide concentrations in biochemical reactions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 164. doi:1538-7445.AM2012-164

Abstract 5445: Universal bioluminescent HTS-formatted assay for quantitation of ADP production in kinase and ATPase reactions

Protein Kinases are implicated in metabolic and cellular disorders including cancer and thus they represent a very important target for the development of novel therapeutics. The process of developing new drug requires an innovative and low cost strategy to screen and identify compounds that can be used for lead optimization that incorporate the required desirable features. It will be idea to have a universal technology that can be used for the various stages of drug discovery such as assay development, compound screening, lead optimization, and enzyme profiling using the same technology platform. The technology should provide high sensitivity, robustness, and low cost. Towards that goal, we have expanded our luminescent platform for monitoring kinase activity to enable us to detect enzyme activity using low amount of enzymes, measure initial rates at very early substrate conversion, and generate reliable and robust data. This luminescent assay monitors enzyme activity by measuring ADP production using a homogenous and high through put formatted assay. The assay is also ideal for profiling compounds against various kinases since it detects ADP, the universal product of all kinases. Thus, the new homogenous assay is most suitable for drug discovery targeting kinases since it can be used in all various stages of drug development leading to animal or cellular studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5445. doi:10.1158/1538-7445.AM2011-5445

Abstract 5335: Dissecting the ubiquitin pathway using homogenous and sensitive bioluminescent assay

Post-translational modification of target proteins by ubiquitin (Ub) and ubiquitin-like (Ubl) proteins is a fundamental mechanism for regulating protein functions and protein stability thus affecting diverse cellular processes. Several ubiquitin-like (Ubl) molecules have been identified including SUMO, NEDD8, ATG8/15 and ISG15 which share the ubiquitin fold Ub/Ubl proteins are conjugated to lysine residues in substrate proteins through an ATP-dependent enzymatic cascade involving E1-activating enzyme, E2-conjugating enzyme and E3-ligase. To mark proteins for degradation, multiple ubiquitins are covalently attached to produce a Lys48 linked poly-ubiquitin chain. The poly-ubiquitinated proteins are recognized by the 26S proteasome system and deubiquitinated and destroyed. Substrates with ubiquitin chains linked through Lys 6, 11, 27, 29, 33 also regulate protein degradation. Substrates marked with mono-ubiquitination or Lys63 ubiquitin chains are involved in cell signaling independent of degradative functions. Many diseases are associated with dysfunction of ubiquitin signaling, with the E3 ligase class of enzymes are considered to be the most important target. However, in recent years, evidence have accumulated demonstrating the significance of E2 class of enzymes where mutations and impairment of this class lead to severe diseases states including chromosomal instability, cancer predisposition, neurological syndromes, and immunological disorders. Thus, in addition to E3, E2 group of enzymes represent important class of therapeutic targets. To address the need for developing drugs targeting these enzymes, we have developed a novel assay that can be used to screen for modulators of these enzymes by taking advantage of the first ubiquitin activating enzyme E1 which activates free Ub forming a high-energy thioester bond between E1’s active site Cys and the C-terminus of Ub, generating AMP and pyrophosphate (PPi) as products of the reaction. We monitor the activity of these enzymes by determining the concentration of AMP generated in the reactions in a luminescence-based assay. Our assay interrogate not only E1 but also E2 and E3 in a very robust and sensitive manner. The assay is homogenous, bioluminescent, and show a very high signal to background in a very selective manner for each class of the ubiquitin pathway. The assay was successfully tested for ubiquitination, SUMOlyation and Neddylation reactions and thus can be used for screening of enzymes targeting these pathways. Citation Format: Said A. Goueli, Kevin Hsiao, Subhanjan Mondal. Dissecting the ubiquitin pathway using homogenous and sensitive bioluminescent assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5335. doi:10.1158/1538-7445.AM2017-5335

Abstract 414: Biochemical and cellular monitoring of the activity of the ecto-5’-nucleotidase (CD73), a key cancer modulator using HTS-formatted bioluminescent technology

The ecto-5’-nucleotidase (CD73) is glycosylphosphatidylinositol (GPI) anchored cell surface protein that is involved in switching on adenosinergic signaling. Its enzymatic and nonenzymatic activities (via its interaction with extracellular matrix components) are involved in cancer associated processes and not completely independent of each other. It catalyzes the hydrolysis of AMP into adenosine and phosphate, where adenosine plays important role in tumor immune escape. It is overexpressed in many types of cancer cell lines and patient9s biopsies including breast, colon, ovarian, gastric, ovarian, etc. In addition to being important as clinical and prognostic marker in cancer patients, overexpression of CD73 is associated with resistance to antitumor agents, and inhibition of CD73 activity or knocking it down by SiRNA reversed chemoresistant phenotype of glioblastoma multiforme cells. Because of the significant role of CD73, it is of importance to develop an assay that monitor the activity of CD73 in order to develop modulators of its activity. Towards this goal, we have developed a bioluminescent assay to monitor the activity of the enzyme in biochemically pure as well cellular anchored enzyme forms. The assay is homogenous and formatted for HTS screening research, very sensitive, and robust as indicated by the high Z’. We also show that the use of inhibitors such as adenosine 5’-(α-β-methylene) diphosphate (APCP) generates data with biochemically pure enzyme similar to the cellular bound form. We also demonstrate that cells that are enriched in CD73 can be easily identified from those that have low CD73. Thus, the current assay is robust, sensitive, and easy to use making it an ideal assay for HTS screening for new modulators of CD73 and generation of potential novel cancer therapeutics Citation Format: Said A. Goueli, Kevin hsiao. Biochemical and cellular monitoring of the activity of the ecto-5’-nucleotidase (CD73), a key cancer modulator using HTS-formatted bioluminescent technology. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 414.

Abstract 5434: A high through-put bioluminescent assay to monitor the deamidation of asparagine and isomerization of aspartate residues in therapeutic proteins and antibodies

Spontaneous degradation reactions such as oxidation, glycation, deamidation, Isomerization, and racemization are non-enzymatic modifications and produce functionally damaged species reflecting aging effect at the molecular level. L-asparagine (Asn) and L-aspartate (Asp) are among the most unstable residues in proteins- linked to deamidation, isomerization and racemization Rx. Under physiological conditions, succinimide-linked deamidation of Asn occurs with t 1/2 as short as 6 hrs while that for isoaspartate are generally 10-fold longer. A number of biological peptides and proteins possess labile Asn and Asp residues and the formation of IsoAsp at these sites adversely affect their function. The degradation of Asn and Asp sites via succinimide pathway has significant effect on protein function. Loss of function associated with isoAsp formation are found in many biologically critical proteins and is a major source of antibody instability and micro heterogeneity, Thus it is critical to accurately determine both the levels and the site of Asn deamidation in therapeutic antibodies and proteins. Although mass Spectroscopic platforms have been at the forefront of technologies to quantitate and identify sites of isoAsp formation, it fails in accurately determining Asn level and has problems with Asp isomerization due to the various steps required for sample preparation such as denaturation, reduction, alkylation, and enzyme digestion of the Ab before analysis resulting in problems with Asp isomerization and Asn determination artifacts. Although peptide mapping is the most powerful tool in isoAsp analyses, it is very time consuming and may itself actually cause sample degradation during preparation and analysis and is not always practical when large number of samples are needed for analysis. To improve on and complement existing technologies, we have developed a bioluminescent, homogenous, robust, sensitive and easy to use assay to accurately monitor the deamidation of Asn and isomerization of aspartate. The assay is based on the use of protein isoaspartate methyltransferase to catalyze the methylation of isoaspartate using S-adenosylmethionine (SAM) and resulting in the formation of S-adenosylhomocysteine and methylated isoaspartate. The assay is very sensitive, it can detect as little as 100 fmol of IsoAsp in as little as 5-10 pmol of proteins. Citation Format: Said A. Goueli, Kevin Hsiao, Rushikesh Patel, Vishal Nashine. A high through-put bioluminescent assay to monitor the deamidation of asparagine and isomerization of aspartate residues in therapeutic proteins and antibodies. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5434. doi:10.1158/1538-7445.AM2015-5434

Abstract 93: Universal homogenous bioluminescent assay that monitor the activity various classes of methyltransferases in vitro

Post transcriptional modifications of proteins and nucleic acids are well-recognized to play major role in influencing cell fate towards cellular proliferation, differentiation, and cell death. Such modifications that include phosphorylation, acetylation, methylation, etc. have been validated as drug targets resulting in the development of several drugs. Recent biochemical and biological data suggest that the enzymatic activities of several of these enzymes have pathogenic roles in cancer, inflammation, and neurodegenerative diseases. Thus, pharmacological modulation of these enzymes by small molecules will be beneficial in developing novel therapeutics for multiple unmet medical needs. Of these, methyltransferases are known to alter the epigenome by altering the methylation status of nucleic acids or proteins resulting in changes in cellular functions. Towards this goal of searching for activators/inhibitors of these enzymes for the development of next generation of drugs, screening assays for these modulators are urgently needed. To address these unmet needs, we have developed a novel assay that monitors the activities of these enzymes and their modulation by small molecules. The assay is bioluminescent based, HTS formatted and highly sensitive. The assay is universal since it is based on monitoring the formation of the universal product S-adenosylhomocysteine (SAH), i.e., capable of detecting changes in activity of a broad range of methyltransferases such as DNA, protein, RNA, and small molecules methyltransferases. In addition, the assay has been validated for all classes of protein methyltransferases (Lysine and Arginine), and with different types of substrates (small peptides, large proteins, or even nucleosomes). This enables determining the specificity of these enzymes and their substrate requirements. The assay has high signal to background and low C.V. The assay is robust (Z’ value > 0.7) and has been validated using various plate densities such as 96-, 384, and 1536-well plates. A strong feature of this assay is its utility with broad range of substrates with no limitations on the use of high concentrations of substrates or the composition of the substrates (short vs. long peptides), thus enabling the generation of kinetic data and determining the mechanism of action of various modulators of methyltransferases of interest. Citation Format: Kevin Hsiao, Said Goueli. Universal homogenous bioluminescent assay that monitor the activity various classes of methyltransferases in vitro. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 93. doi:10.1158/1538-7445.AM2015-93