Confocal Raman characterization of different protein desorption behaviors from chromatographic particles.

Confocal Raman spectroscopy is a nondestructive analytical technique that combines the chemical information from vibrational spectroscopy with the spatial resolution of confocal microscopy. It was applied, for the first time, to measure protein desorption from chromatographic particles. Monoclonal antibody was loaded onto the Fractogel EMD SO3 (M) cation exchanger at either pH 5 or pH 4. Confocal Raman measurement suggests that only the protein loaded at pH 5 is able to release from chromatographic particles in the elution buffer. Detailed comparison of high-quality spectra indicates that, while proteins loaded at both pH values showed a predominant ß-sheet conformation, protein loaded at pH 4 has a broader amide I band with more intensity in the >1680 cm(-1) region. This small but clear and reproducible amide I bandwidth increase is not observed for protein in the solution state at pH 4. No definitive assignment of the increased Raman intensity in the >1680 cm(-1) region could be made, but it might be related to structural changes involved in the association of protein molecules in the adsorbed state, which helps to explain the nearly 100% retention under elution conditions of the monoclonal antibody adsorbed at pH 4 in chromatographic particles.

Sequential multiplex analyte capturing for phosphoprotein profiling.

Microarray-based sandwich immunoassays can simultaneously detect dozens of proteins. However, their use in quantifying large numbers of proteins is hampered by cross-reactivity and incompatibilities caused by the immunoassays themselves. Sequential multiplex analyte capturing addresses these problems by repeatedly probing the same sample with different sets of antibody-coated, magnetic suspension bead arrays. As a miniaturized immunoassay format, suspension bead array-based assays fulfill the criteria of the ambient analyte theory, and our experiments reveal that the analyte concentrations are not significantly changed. The value of sequential multiplex analyte capturing was demonstrated by probing tumor cell line lysates for the abundance of seven different receptor tyrosine kinases and their degree of phosphorylation and by measuring the complex phosphorylation pattern of the epidermal growth factor receptor in the same sample from the same cavity.

A Generic Procedure for the Isolation of pH- and Magnesium-Responsive Chicken scFvs for Downstream Purification of Human Antibodies.

Affinity chromatography provides an excellent platform for protein purification, which is a key step in the large scale downstream processing of therapeutic monoclonal antibodies (Mabs). Protein A chromatography constitutes the gold standard for Mab purification. However, the required acidic conditions (2.8-3.5) for elution from the affinity matrix limit their applicability, particularly for next generation antibodies and antibody fusion proteins, since denaturation and irreversible aggregation can occur due to the acidic buffer conditions. Here we describe a generic procedure for the generation of antigen-specific chromatography ligands with tailor-made elution conditions. To this end, we generated a scFv-library based on mRNA from a chicken immunized with human Fc. The antibody repertoire was displayed on yeast Saccharomyces cerevisiae screened via FACS toward pH- and magnesium-responsive scFvs which specifically recognize human IgG antibodies. Isolated scFvs were reformatted, produced in Escherichia coli and immobilized on NHS-agarose columns. Several scFvs were identified that mediated antibody binding at neutral pH and antibody recovery at pH values of 4.5 and higher or even at neutral pH upon MgCl2 exposure. The iterative screening methodology established here is generally amenable to the straightforward isolation of stimulus-responsive antibodies that may become valuable tools for a variety of applications.

Microsphere-based co-immunoprecipitation in multiplex.

Co-immunoprecipitation (co-IP) is a prominent technique for evaluating protein-protein interactions. Currently, large quantities of protein are required to perform co-IP followed by mass spectrometric or Western blot analyses of the interacting proteins. Here catenin-cadherin complexes were employed to establish a multiplexed microsphere-based co-immunoprecipitation (micro co-IP) protocol that allows the analysis of different complexes of a given protein with various interacting proteins within a single experiment using a limited amount of sample material.

Sphingolipid metabolism in neural cells.

Sphingolipids were discovered more than a century ago in the brain. Cerebrosides and sphingomyelins were named so because they were first isolated from neural tissue. Although glycosphingolipids and especially those containing sialic acid in their oligosaccharide moiety are particularly abundant in the brain, sphingolipids are ubiquitous cellular membrane components. They form cell- and species-specific profiles at the cell surfaces that characteristically change in development, differentiation, and oncogenic transformation, indicating the significance of these lipid molecules for cell-cell and cell-matrix interactions as well as for cell adhesion, modulation of membrane receptors and signal transduction. This review summarizes sphingolipid metabolism with emphasis on aspects particularly relevant in neural cell types, including neurons, oligodendrocytes and neuroblastoma cells. In addition, the reader is briefly introduced into the methodology of lipid evaluation techniques and also into the putative physiological functions of glycosphingolipids and their metabolites in neural tissue.

Exploiting features of adenovirus replication to support mammalian kinase production.

Faced with the current wealth of genomic data, it is essential to have robust and reliable methods of converting DNA sequences into their functional gene products. We demonstrate here that when conditions are established that take advantage of the replication-associated virus amplification, the virus-induced shutdown of host protein synthesis as well as the activation of signalling pathways that normally occur during virus replication, adenovirus biology can be exploited to generate a potent kinase expression system. Residual virus in the protein production has always been a limitation for adenovirus systems and we describe a DNA intercalator/ultraviolet light treatment that eliminates residual adenovirus in protein preparations that has no deleterious effect on enzyme activity. The use of mammalian cells in combination with adenovirus generated a variety of active enzymes which could not be produced in Escherichia coli or baculovirus-infected insect cells. Thus, the utility of adenovirus-mediated enzyme expression as a versatile alternative to established protein production technologies is demonstrated.

Identification of inhibitors for a virally encoded protein kinase by 2 different screening systems: in vitro kinase assay and in-cell activity assay.

The human cytomegalovirus (HCMV) protein kinase pUL97 represents an important determinant for viral replication and thus is a promising target for the treatment of HCMV. The authors screened a compound library of nearly 5000 entities based on known kinase inhibitors in 2 distinct ways. A radioactive in vitro kinase assay was performed with recombinant pUL97, purified from baculovirus-infected insect cells, on myelin basic protein-coated FlashPlates. About 20% of all compounds tested inhibited pUL97 kinase activity by more than 50% at a concentration of 10 microM. These hits belonged to various structural classes. To elucidate their potential to inhibit pUL97 in a cellular context, all compounds of the library were also tested in a cell-based activity assay. For this reason, a HEK293 cell line was established that ectopically expressed pUL97. When these cells were incubated with ganciclovir (GCV), pUL97 phosphorylated GCV to its monophosphate, which subsequently became phosphorylated to cytotoxic metabolites by cellular enzymes. Thereby, pUL97 converted cells into a GCV-sensitive phenotype. Inhibition of the pUL97 kinase activity resulted in protection of the cells against the cytotoxic effects of GCV. In total, 199 compounds of the library were cellular active at nontoxic concentrations, and 93 of them inhibited pUL97 in the in vitro kinase assay. Among these, promising inhibitors of HCMV replication were identified. The 2-fold screening system described here should facilitate the development of pUL97 inhibitors into potent drug candidates.

Host cell targets in HCV therapy: novel strategy or proven practice?

The development of novel antiviral drugs against hepatitis C is a challenging and competitive area of research. Progress of this research has been hampered due to the quasispecies nature of the hepatitis C virus, the absence of cellular infection models and the lack of easily accessible and highly representative animal models. The current combination therapy consisting of interferon-alpha and ribavirin mainly acts by supporting host cell defence. These therapeutics are the prototypic representatives of indirect antiviral agents as they act on cellular targets. However, the therapy is not a cure, when considered from the long-term perspective, for almost half of the chronically infected patients. This draws attention to the urgent need for more efficient treatments. Novel anti-hepatitis C treatments under study are directed against a number of so-called direct antiviral targets such as polymerases and proteases, which are encoded by the virus. Although such direct antiviral approaches have proven to be successful in several viral indications, there is a risk of resistant viruses developing. In order to avoid resistance, the development of indirect antiviral compounds has to be intensified. These act on host cell targets either by boosting the immune response or by blocking the virus host cell interaction. A particularly interesting approach is the development of inhibitors that interfere with signal transduction, such as protein kinase inhibitors. The purpose of this review is to stress the importance of developing indirect antiviral agents that act on host cell targets. In doing so, a large source of potential targets and mechanisms can be exploited, thus increasing the likelihood of success. Ultimately, combination therapies consisting of drugs against direct and indirect viral targets will most probably provide the solution to fighting and eradicating hepatitis C virus in patients.

Protein kinase C eta is associated with progression of renal cell carcinoma (RCC).

BACKGROUND: The expression of all eleven PKC-isoforms in clear cell RCCs (ccRCC) and in the corresponding normal renal tissue was quantified. A possible association of PKC-isoforms with histopathological parameters was examined. MATERIALS AND METHODS: Proteins were isolated from tumor and normal tissue of 43 patients with ccRCC. Expression of PKC-isoforms were quantified by Western blot analysis. RESULTS: In both, ccRCCs and the corresponding normal renal tissue, all PKC-isoforms apart from PKC gamma and theta were detectable. Striking associations between PKC-isoforms and histopathological parameters were observed: (i) a 3-fold increase in PKC eta of grade 3 and 4 versus grade 1 and 2 tumors (p = 0.025), (ii) a decrease of PKC alpha in tumor versus normal tissue of 18% (p = 0.020) and (iii) a 20% increase of PKC zeta in grade 3 and 4 versus grade 1 and 2 tumors (p = 0.092). CONCLUSION: The major result is a clear correlation of PKC eta expression with tumor progression. This observation-is in agreement with the known oncogenic properties of PKC eta. Similarly, oncogenic PKC zeta also increased with tumor progression. PKC alpha, with known tumor-suppressor properties, was decreased in ccRCC versus normal tissue. These findings may become important for both classification and treatment of ccRCC.

Receptor tyrosine kinase inhibitor profiling using bead-based multiplex sandwich immunoassays.

Receptor tyrosine kinases (RTK) are important targets in drug discovery processes. Studying the phosphorylation pattern of RTKs enables the determination of their activation and inactivation states. Multiplex bead-based sandwich immunoassays are powerful tools for measuring the phosphorylation state of key regulators within cellular signalling networks. Here, we describe the analysis of the phosphorylation state of receptor tyrosine kinases using the epidermal growth factor receptor (EGFR) as an example. We provide a protocol for a bead-based sandwich immunoassay that enables a relative quantification of the EGFR and its generic tyrosine phosphorylation. We also present data from a kinase inhibitor experiment using 96-well cell-culture plates and a commercially available kit for the analysis of seven receptor tyrosine kinases.

Evaluation of a urinary kidney biomarker panel in rat models of acute and subchronic nephrotoxicity.

Several novel urinary kidney biomarkers were recently approved by the US-FDA and EMA for improved detection of nephrotoxicity, but few data regarding their performance are publicly available so far. In this study, we investigated the potential of some of the newly accepted makers (Kim-1, ß-2-microglobulin, cystatin C, clusterin) along with six additional urinary key proteins of kidney injury (GST-α, Timp-1, VEGF, calbindin, NGAL/lipocalin-2, osteopontin) to detect proximal tubule damage in the rat model studying either acute drug-induced kidney injury or subchronic nephrotoxicity. Candidate proteins were measured in urine samples obtained from rats treated with gentamicin (0, 60 and 120 mg/kg bw for 7 days), BI-3 [3-pyrrolidineacetic acid, 5-[[[4'-[imino[(methoxycarbonyl) amino]methyl] [1,1'-biphenyl]-4-yl]oxy]methyl]-2-oxo-, methyl ester,(3S-trans)] (0, 100, and 1000 mg/kg bw for up to 14 days) or with the mycotoxin ochratoxin A (OTA) (0, 21, 70 and 210 µg/kg bw for up to 90 days) using a Luminex(®) xMAP(®) platform. Cystatin C and NGAL appeared to be the most sensitive indicators of gentamicin nephrotoxicity, with significant changes occurring as early as day 1, and importantly before alterations in serum creatinine or blood urea nitrogen (BUN). Altered urinary excretion of KIM-1, clusterin, calbindin and Timp-1 accompanied by a rise in BUN was observed in rats with BI-3 at 1000 mg/kg bw for 14 days. In contrast, histopathological alterations induced by OTA, which preceded effects on traditional clinical parameters, were best reflected by changes in urinary Kim-1. Overall, our data confirm increased sensitivity of new markers as compared to traditional clinical chemistry parameters.

Expression of gastrointestinal glutathione peroxidase is inversely correlated to the presence of hepatitis C virus subgenomic RNA in human liver cells.

There is great medical need to develop novel therapies for treatment of human hepatitis C virus (HCV). By gene expression analysis of three HCV-subgenomic RNA replicon cell lines, we identified cellular proteins whose expression is affected by the presence of HCV and therefore may serve as drug targets. Data from cDNA array filter hybridization, as well as from Northern and Western blotting, revealed that the gastrointestinal-glutathione peroxidase (GI-GPx) was drastically down-regulated (up to 20-fold) in all replicon cell lines tested. Concomitantly, total cellular glutathione peroxidase activity was drastically reduced, which rendered these human liver cells more susceptible toward oxidative stress. Interferon alpha caused down-regulation of the HCV-replicon followed by recovery of GI-GPx expression to nearly normal levels. Furthermore, expression of GI-GPx in replicon cells by gene transduction caused down-regulation of HCV RNA in a dose-dependent manner. Moreover, activating the endogenous gene coding for GI-GPx by all-trans-retinoic acid (RA) was sufficient to cause down-regulation of the HCV replicon. A small interfering RNA duplex abrogated GI-GPx up-regulation by RA and concomitantly suppression of HCV. The RA effect was dependent on the presence of sodium selenite, was reversible, and was independent of RNA-activated protein kinase. Taken together, these results show that HCV inhibits the expression of GI-GPx in replicon cells to promote its intracellular propagation. Modulation of GI-GPx activity may open new avenues of treatment for HCV patients.

The 3'-UTR of the mRNA coding for the major protein kinase C substrate MARCKS contains a novel CU-rich element interacting with the mRNA stabilizing factors HuD and HuR.

The expression of the major protein kinase C substrate MARCKS (myristoylated alanine-rich C kinase substrate) is controlled by the stability of its mRNA. While the MARCKS mRNA is long living in quiescent fibroblasts (t1/2 = 14 h), its half-life time is drastically reduced (t1/2 = 2 h) in cells treated with phorbol esters to activate protein kinase C (PKC) or treated with growth factors. In a first step to study the underlying mechanism we identified both a cis-element on the MARCKS mRNA and the corresponding trans-acting factors. Fusing the complete 3'-UTR or specific regions of the 3'-UTR of the MARCKS gene to a luciferase reporter gene caused a drastic decrease in luciferase expression to as low as 5-10% of controls. This down-regulation was a result of destabilization of the chimeric transcript as shown by RNA run-off and Northern blot-assays. By RNase/EMSA and UV-cross-linking experiments, we identified a stretch of 52 nucleotides [(CUUU)11(U)8] in the 3'-UTR of the MARCKS mRNA specifically recognized by two RNA-binding proteins, HuD and HuR. These trans-acting factors are members of the ELAV gene family and bind the MARCKS CU-rich sequence with high affinity. Overexpression of HuD and HuR in murine fibroblasts caused a striking stabilization of the endogenous MARCKS mRNA even under conditions when the MARCKS mRNA is normally actively degraded, i.e. after treating cells with phorbol ester. These data imply, that the identified CU-rich cis-element of the MARCKS 3'-UTR is involved in conferring instability to mRNAs and that members of the ELAV gene family oppose this effect. Based on its structural and functional properties, the (CUUU)11(U)8 sequence described here can be grouped into class III of AU-rich elements.

Novel chemical class of pUL97 protein kinase-specific inhibitors with strong anticytomegaloviral activity.

Human cytomegalovirus (HCMV) is a major human pathogen frequently associated with life-threatening disease in immunosuppressed patients and newborns. The HCMV UL97-encoded protein kinase (pUL97) represents an important determinant of viral replication. Recent studies demonstrated that pUL97-specific kinase inhibitors are powerful tools for the control of HCMV replication. We present evidence that three related quinazoline compounds are potent inhibitors of the pUL97 kinase activity and block in vitro substrate phosphorylation, with 50% inhibitory concentrations (IC(50)s) between 30 and 170 nM. Replication of HCMV in primary human fibroblasts was suppressed with a high efficiency. The IC(50)s of these three quinazoline compounds (2.4 +/- 0.4, 3.4 +/- 0.6, and 3.9 +/- 1.1 microM, respectively) were in the range of the IC(50) of ganciclovir (1.2 +/- 0.2 microM), as determined by the HCMV green fluorescent protein-based antiviral assay. Importantly, the quinazolines were demonstrated to have strong inhibitory effects against clinical HCMV isolates, including ganciclovir- and cidofovir-resistant virus variants. Moreover, in contrast to ganciclovir, the formation of resistance to the quinazolines was not observed. The mechanisms of action of these compounds were confirmed by kinetic analyses with infected cells. Quinazolines specifically inhibited viral early-late protein synthesis but had no effects at other stages of the replication cycle, such as viral entry, consistent with a blockage of the pUL97 function. In contrast to epithelial growth factor receptor inhibitors, quinazolines affected HCMV replication even when they were added hours after virus adsorption. Thus, our findings indicate that quinazolines are highly efficient inhibitors of HCMV replication in vitro by targeting pUL97 protein kinase activity.

Loss of tumor suppressor protein PTEN during renal carcinogenesis.

The tumor suppressor gene PTEN (phosphatase and tensin homologue deleted from chromosome 10) encodes a dual specific protein and phospholipid phosphatase that affects cell proliferation, apoptosis and migration. In our study, we examined protein expression of PTEN in renal carcinogenesis. PTEN protein levels were examined in 42 clear cell renal cell carcinomas (ccRCC) and oncocytomas as well as in the corresponding normal renal tissue of the same patients using Western blot analysis. Cellular localization was analyzed by immunohistochemistry. PTEN was highly expressed in all investigated normal renal tissue specimens. Immunohistochemical analysis showed an almost exclusive staining of proximal tubulus epithelial cells known to be precursor cells of ccRCC. Within the proximal tubulus cells, PTEN exhibited a membrane predominant immunostaining pattern. In ccRCCs PTEN expression was markedly reduced to an average of less than 10% compared with normal tissue as evidenced by Western blot analysis (p < 0.001). The degree of reduction was similar in highly differentiated (G1) carcinomas and in less differentiated (G2-G4) carcinomas. These observations were reproduced by immunohistochemical studies, which revealed a loss of the characteristic membrane predominant immunostaining pattern in ccRCC. In contrast to the PTEN positive proximal tubulus epithelial cells, the distal tubulus epithelial cells, which are precursor cells of the benign oncocytomas, exhibited only a very weak PTEN expression. Compared with the distal tubulus epithelial cells, no downregulation of PTEN was seen in oncocytomas. We conclude that PTEN expression and PTEN membrane localization are lost during early renal cell carcinogenesis and may therefore be a valuable RCC tumor marker.

Identification and characterization of amphiphysin II as a novel cellular interaction partner of the hepatitis C virus NS5A protein.

The hepatitis C virus (HCV) NS5A protein is highly phosphorylated by cellular protein kinases. To study how NS5A might be integrated in cellular kinase signalling, we isolated phosphoproteins from HuH-7 hepatoma cells that specifically interacted with recombinant NS5A protein. Subsequent mass spectrometry identified the adaptor protein amphiphysin II as a novel interaction partner of NS5A. Mutational analysis revealed that complex formation is primarily mediated by a proline-rich region in the C-terminal part of NS5A, which interacts with the amphiphysin II Src homology 3 domain. Importantly, we could further demonstrate specific co-precipitation and cellular co-localization of endogenous amphiphysin II with NS5A in HuH-7 cells carrying a persistently replicating subgenomic HCV replicon. Although the NS5A-amphiphysin II interaction appeared to be dispensable for replication of these HCV RNAs in cell culture, our results indicate that NS5A-amphiphysin II complex formation might be of physiological relevance for the HCV life cycle.