Versatile Histochemical Approach to Detection of Hydrogen Peroxide in Cells and Tissues Based on Puromycin Staining.

Hydrogen peroxide (H2O2) is a central reactive oxygen species (ROS) that contributes to diseases from obesity to cancer to neurodegeneration but is also emerging as an important signaling molecule. We now report a versatile histochemical approach for detection of H2O2 that can be employed across a broad range of cell and tissue specimens in both healthy and disease states. We have developed a first-generation H2O2-responsive analogue named Peroxymycin-1, which is based on the classic cell-staining molecule puromycin and enables covalent staining of biological samples and retains its signal after fixation. H2O2-mediated boronate cleavage uncages the puromycin aminonucleoside, which leaves a permanent and dose-dependent mark on treated biological specimens that can be detected with high sensitivity and precision through a standard immunofluorescence assay. Peroxymycin-1 is selective and sensitive enough to image both exogenous and endogenous changes in cellular H2O2 levels and can be exploited to profile resting H2O2 levels across a panel of cell lines to distinguish metastatic, invasive cancer cells from less invasive cancer and nontumorigenic counterparts, based on correlations with ROS status. Moreover, we establish that Peroxymycin-1 is an effective histochemical probe for in vivo H2O2 analysis, as shown through identification of aberrant elevations in H2O2 levels in liver tissues in a murine model of nonalcoholic fatty liver disease, thus demonstrating the potential of this approach for studying disease states and progression associated with H2O2. This work provides design principles that should enable development of a broader range of histochemical probes for biological use that operate via activity-based sensing.

Cell type-selective imaging and profiling of newly synthesized proteomes by using puromycin analogues.

We have developed a versatile antibody-assisted strategy for the imaging and profiling of newly synthesized proteomes in a cell-specific manner. This strategy remained highly selective even in heterogeneous co-cultured cells, thus enabling labeling and enrichment of nascent proteomes from targeted cells without the need for physical separation.

Synthesis, in Vitro Evaluation, and Radiolabeling of Fluorinated Puromycin Analogues: Potential Candidates for PET Imaging of Protein Synthesis.

There is currently no ideal radiotracer for imaging of protein synthesis rate (PSR) by positron emission tomography (PET). Existing fluorine-18-labeled amino acid-based radiotracers predominantly visualize amino acid transporter processes, and in many cases they are not incorporated into nascent proteins at all. Others are radiolabeled with the short-half-life positron emitter carbon-11, which is rather impractical for many PET centers. Based on the puromycin (6) structural manifold, a series of 10 novel derivatives of 6 was prepared via Williamson ether synthesis from a common intermediate. A bioluminescence assay was employed to study their inhibitory action on protein synthesis, which identified the fluoroethyl analogue 7b as a lead compound. The fluorine-18 analogue was prepared via nucleophilic substitution of the corresponding tosylate precursor in a modest radiochemical yield of 2 ± 0.6% with excellent radiochemical purity (>99%) and showed complete stability over 3 h at ambient temperature.

Detection of O-propargyl-puromycin with SUMO and ubiquitin by click chemistry at PML-nuclear bodies during abortive proteasome activities.

The amino-nucleoside antibiotic, puromycin, acts by covalently linking to elongating polypeptide chains on ribosomes to generate prematurely terminated immature polypeptides. The trafficking of puromycin-conjugated (puromycylated) immature polypeptides within cell has, however, remained elusive. In this study, using O-propargyl-puromycin (OP-Puro), the distribution of puromycylated polypeptides was assessed in HeLa cells by click chemistry. Under standard culture conditions, OP-Puro signals were detected in the cytoplasm and nucleus with the highest concentrations in the nucleolus. Intriguingly, when proteasome activities were aborted using MG132, OP-Puro signals began to accumulate at promyelocytic leukemia nuclear bodies (PML-NBs) in addition to the nucleolus. We also found promiscuous association of OP-Puro signals with SUMO-2/3 and ubiquitin at PML-NBs, but not at the nucleolus, during abortive proteasome activities. This study reveals a previously unknown distribution of OP-Puro that argues for a nuclear function in regulating immature protein homeostasis.

Application of a nonradioactive method of measuring protein synthesis in industrially relevant Chinese hamster ovary cells.

Due to the high medical and commercial value of recombinant proteins for clinical and diagnostic purposes, the protein synthesis machinery of mammalian host cells is the subject of extensive research by the biopharmaceutical industry. RNA translation and protein synthesis are steps that may determine the extent of growth and productivity of host cells. To address the problems of utilization of current radioisotope methods with proprietary media, we have focused on the application of an alternative method of measuring protein synthesis in recombinant Chinese hamster ovary (CHO) cells. This method employs puromycin as a nonradioactive label which incorporates into nascent polypeptide chains and is detectable by western blotting. This method, which is referred to as SUnSET, successfully demonstrated the expected changes in protein synthesis in conditions that inhibit and restore translation activity and was reproducibly quantifiable. The study of the effects of feed and sodium butyrate addition on protein synthesis by SUnSET revealed an increase following 1 h feed supplementation while a high concentration of sodium butyrate was able to decrease translation during the same treatment period. Finally, SUnSET was used to compare protein synthesis activity during batch culture of the CHO cell line in relation to growth. The results indicate that as the cells approached the end of batch culture, the global rate of protein synthesis declined in parallel with the decreasing growth rate. In conclusion, this method can be used as a "snapshot" to directly monitor the effects of different culture conditions and treatments on translation in recombinant host cells.

Nuclear translation visualized by ribosome-bound nascent chain puromycylation.

Whether protein translation occurs in the nucleus is contentious. To address this question, we developed the ribopuromycylation method (RPM), which visualizes translation in cells via standard immunofluorescence microscopy. The RPM is based on ribosome-catalyzed puromycylation of nascent chains immobilized on ribosomes by antibiotic chain elongation inhibitors followed by detection of puromycylated ribosome-bound nascent chains with a puromycin (PMY)-specific monoclonal antibody in fixed and permeabilized cells. The RPM correlates localized translation with myriad processes in cells and can be applied to any cell whose translation is sensitive to PMY. In this paper, we use the RPM to provide evidence for translation in the nucleoplasm and nucleolus, which is regulated by infectious and chemical stress.

SUnSET, a nonradioactive method to monitor protein synthesis.

We developed a nonradioactive fluorescence-activated cell sorting-based assay, called surface sensing of translation (SUnSET), which allows the monitoring and quantification of global protein synthesis in individual mammalian cells and in heterogeneous cell populations. We demonstrate here, using mouse dendritic and T cells as a model, that SUnSET offers a technical alternative to classical radioactive labeling methods for the study of mRNA translation and cellular activation.

Chlorolissoclimides: new inhibitors of eukaryotic protein synthesis.

Lissoclimides are cytotoxic compounds produced by shell-less molluscs through chemical secretions to deter predators. Chlorinated lissoclimides were identified as the active component of a marine extract from Pleurobranchus forskalii found during a high-throughput screening campaign to characterize new protein synthesis inhibitors. It was demonstrated that these compounds inhibit protein synthesis in vitro, in extracts prepared from mammalian and plant cells, as well as in vivo against mammalian cells. Our results suggest that they block translation elongation by inhibiting translocation, leading to an accumulation of ribosomes on mRNA. These data provide a rationale for the cytotoxic nature of this class of small molecule natural products.

Yeast initiator tRNA identity elements cooperate to influence multiple steps of translation initiation.

All three kingdoms of life employ two methionine tRNAs, one for translation initiation and the other for insertion of methionines at internal positions within growing polypeptide chains. We have used a reconstituted yeast translation initiation system to explore the interactions of the initiator tRNA with the translation initiation machinery. Our data indicate that in addition to its previously characterized role in binding of the initiator tRNA to eukaryotic initiation factor 2 (eIF2), the initiator-specific A1:U72 base pair at the top of the acceptor stem is important for the binding of the eIF2.GTP.Met-tRNA(i) ternary complex to the 40S ribosomal subunit. We have also shown that the initiator-specific G:C base pairs in the anticodon stem of the initiator tRNA are required for the strong thermodynamic coupling between binding of the ternary complex and mRNA to the ribosome. This coupling reflects interactions that occur within the complex upon recognition of the start codon, suggesting that these initiator-specific G:C pairs influence this step. The effect of these anticodon stem identity elements is influenced by bases in the T loop of the tRNA, suggesting that conformational coupling between the D-loop-T-loop substructure and the anticodon stem of the initiator tRNA may occur during AUG codon selection in the ribosomal P-site, similar to the conformational coupling that occurs in A-site tRNAs engaged in mRNA decoding during the elongation phase of protein synthesis.

A practical route to 3'-amino-3'-deoxyadenosine derivatives and puromycin analogues.

3'-aminoacylamino-3'-deoxyadenosines, analogues of the antibiotic puromycin, have been synthesized from adenosine. They key 3'-azido derivative 10 was obtained through a 3'-oxidation/reduction/substitution procedure. A modified purification protocol on a larger scale was developed for the oxidation step using the Garegg reagent. The coupling reaction between an Fmoc-l-amino acid and the fully protected form of 3'-amino-3'-deoxyadenosine 11 furnished the aminoacylated compounds 12 in high yields. The puromycin analogues were obtained in 10 steps and up to 23% (14c) overall yield.

Substituted purines elicit differential cytokinetic, molecular and phenotypic effects in HL-60 cells.

This study investigated and compared the cytokinetic, phenotypic and molecular effects elicited in HL-60 human leukemic cells by low doses (0.6 microM) of 3 closely related, substituted purines, puromycin (PM), puromycin aminonucleoside (PAN) and 6-dimethylaminopurine (6-DMAP). PM, but not 6-DMAP or PAN, inhibited [14C]leucine incorporation, induced a time-related cytotoxic effect, a G2-arrest, a metaphase-mitotic-arrest, apoptosis and c-myc mRNA superinduction. PAN and 6-DMAP exerted no detectable morphological or cytokinetic effects, although exposure to these drugs resulted in downregulation of c-myc mRNA levels. We suggest that the specific effects exerted by PM relate to the generation of nascent peptidyl-PM complexes by PM, but not by 6-DMAP or PAN.

Application of high-performance liquid chromatography to the reconstitution of ribosomal subunits.

We are currently utilizing reversed-phase high-performance liquid chromatography (RP-HPLC) in reconstitution experiments designed to study the structure and function of Escherichia coli ribosomes. The applications of RP-HPLC in these experiments include: (a) preparation of individual proteins or groups of proteins on a milligram scale for reconstitution pools, (b) analysis of the protein stoichiometry of reconstituted subunits, (c) determination of the extent and specificity of modification of proteins extracted from ribosomal subunits which have been subjected to chemical modification, and (d) resolution of modified forms of proteins S14 and L23 from the corresponding unmodified proteins. Proteins prepared by RP-HPLC from 30S and 50S ribosomal subunits were found to reconstitute into 30S and 50S subunits respectively, as well as into slower sedimenting particles. The reconstituted subunits contain a full complement of proteins and are active in ribosomal function assays, whereas the slower sedimenting particles lack several proteins and have little or no activity.

The preparation of puromycin antibody and its use in enzyme immunoassay for the quantification using beta-D-galactosidase as a label.

An antibody specific for puromycin (PU) was prepared by immunization of rabbits with a PU conjugate of bovine serum albumin, which was newly synthesized by coupling PU to mercaptosuccinylated bovine serum albumin via a cross-linker, N-(gamma-maleimidobutyryloxy)succinimide. Enzyme labeling of PU was performed using beta-D-galactosidase [EC 3.2.1.23] via N-(m-maleimidobenzoyloxy) succinimide. An ultrasensitive and specific enzyme immunoassay for PU was developed utilizing these reagents by a double antibody technique. The standard curve of the assay was linear in the range of 2 pg to 100 pg, and the lower limit of detection was 28.2 pm (2 pg/tube); so the enzyme immunoassay was found to be approximately 326,000 times more sensitive than a microbiological assay. Further, the enzyme immunoassay is free from interference by any purine or pyrimidine analogs, or by other drugs commonly used for the inhibition of protein synthesis. Using this assay, drug levels were easily determined in rat tissue following PU administration. Since PU is extensively available as an inhibitor of protein synthesis, the enzyme immunoassay should provide useful tool for developing biochemical and toxicity studies of PU.

Biogenesis of endoplasmic reticulum membranes. II. Synthesis of constitutive microsomal enzymes in developing rat hepatocyte.

The constitutive enzymes of microsomal membranes were investigated during a period of rapid ER development (from 3 days before to 8 days after birth) in rat hepatocytes. The activities studied (electron transport enzymes and phosphatases) appear at different times and increase at different rates. The increase in the enzyme activities tested was inhibited by Actinomycin D and puromycin. G-6-Pase and NADPH-cytochrome c reductase activities appeared first in the rough microsomes, and subsequently in smooth microsomes, eventually reaching a uniform concentration as in adult liver. The evidence suggests that the enzymes are synthesized in the rough part, then transferred to the smooth part, of the ER. Changes in the fat supplement of the maternal diet brought about changes in the fatty acid composition of microsomal phospholipids but did not influence the enzymic pattern of the suckling. Microsomes from 8-day-old and adult rats lose 95% of PLP and 80% of NADH-cytochrome c reductase activity after acetone-H(2)O (10:1) extraction. However, one-half the original activity could be regained by adding back phospholipid micelles prepared from purified phospholipid, or from lipid extracts of heart mitochondria, or of liver microsomes of 8-day or adult rats, thus demonstrating an activation of the enzyme by nonspecific phospholipid. The results suggest that during development the enzymic pattern is not influenced by the fatty acid or phospholipid composition of ER membranes.