Secreted proteins play a pivotal role in cellular functions. To better understand malignant behavior, we adapted stable isotopic labeling with amino acids in cell culture technology to identify and quantify proteins differentially released into the extracellular media by a pair of normal and malignant breast-cancer cell lines. Approximately 380 non-redundant proteins were quantified in serum-free media. Of the assigned proteins, 62% are classified secreted in protein databases and an additional 25% are designated secreted in the literature. A number of growth factors were found differentially regulated. Tumor necrosis factor, pigment epithelial-differentiating factor and stem-cell growth factor precursor showed decreased expression in breast-cancer cell line, whereas Inhibin beta and macrophage migration inhibitory factor show increased expression. Interestingly, protease inhibitors, including plasma protease (C1) inhibitor, PZP precursor, and SerpinE2 were significantly down-regulated in cancer cell line as were angiostatic factors from extracellular matrix (ECM) such as endorepillin. Further, the C-terminal fragment of type XVIII collagen, endostatin, a potent angiostatic factor, was down-regulated as well whereas extracellular collagens and osteoblast-specific factor 2 (OSF-2), were up-regulated. Differential expression and secretion of SerpinE2 and OSF-2 were confirmed using Western blotting. These results corroborate models of invasive tumors sustained by elaborate coordination of stromal cells via chemokines and growth factors, while protease inhibitors remodel the ECM to stimulate angiogenesis.
Eight analogs of cholesterol (1) containing a benzophenone group have been synthesized as prospective photoaffinity labels for studies in cellular sterol efflux and HDL formation. Six of these compounds (4-9) have the photophore replacing different portions of the cholesterol alkyl side chain, and two (10 and 11) have it attached via nitrogen at carbon 3. The suitability of these analogs as cholesterol surrogates was determined by examining their ability to replace [3H]1 in fibroblasts preequilibrated with [3H]1. All eight analogs were effective in replacing natural 1 in competition with [3H]1 for apolipoprotein A-I-induced efflux. These are the first compounds shown to replace cholesterol successfully in a complex pathway of multiple intracellular steps. The results suggest an unexpected tolerance of biological membranes regarding the incorporation of sterols of differing chemical structure.
Phospholipid transfer protein (PLTP) is an important regulator of high-density lipoprotein (HDL) metabolism. The two main functions of PLTP are transfer of phospholipids between lipoprotein particles and modulation of HDL size and composition in a process called HDL conversion. These PLTP-mediated processes are physiologically important in the transfer of surface remnants from lipolyzed triglyceride-rich lipoproteins to nascent HDL particles and in the generation of preβ-HDL, the initial acceptor of excess peripheral cell cholesterol. The aim of the study presented here was to investigate the interrelationship between the two functions of PLTP. Plasma PLTP was chemically modified using diethylpyrocarbonate or ethylmercurithiosalicylate. The modified proteins displayed a dose-dependent decrease in phospholipid transfer activity and a parallel decrease in the ability to cause HDL conversion. Two recombinant PLTP mutant proteins, defective in phospholipid transfer activity due to a mutation in the N-terminal lipid-binding pocket, were produced, isolated, and incubated together with radioactively labeled HDL3. HDL conversion was analyzed using three methods: native gradient gel electrophoresis, ultracentrifugation, and crossed immunoelectrophoresis. The results demonstrate that the mutant proteins (i) are able to induce only a modest increase in HDL particle size compared to the wild-type protein, (ii) are unable to release apoA-I from HDL3, and (iii) do not generate preβ-mobile particles following incubation with HDL3. These data suggest that phospholipid transfer is a prerequisite for HDL conversion and demonstrate the close interrelationship between the two main activities of PLTP.
Liver X receptor (LXR) regulates the transcription of ATP-binding cassette transporter A1 (ABCA1) by binding to the DR-4 promoter element as a heterodimer with retinoid X receptor (RXR). The role of chromatin remodeling complex in LXR or ABCA1 activation has not been established previously. In this study, we investigated the activation of ABCA1 by brahma-related gene 1 (BRG-1) and brahma, members of the SWI/SNF (mating type switching/sucrose nonfermenting) chromatin remodeling complex.Overexpression of wild-type BRG-1 in SW-13 cells, but not a catalytically inactive mutant, increased ABCA1 mRNA levels determined by RT-PCR. These effects were enhanced by LXR and RXR agonists. In 293T (epithelial kidney cell line) and Hep3B (hepatocyte cell line) cells, small interfering RNA against BRG-1/brm also affected ABCA1 mRNA levels. Synergistic activation of ABCA1 was obtained after coexpressing BRG-1 and SRC-1, a coactivator of LXR. Luciferase assays showed that this activation of ABCA1 was dependent on the promoter DR-4 element. Coimmunoprecipitation and chromatin immunoprecipitation studies indicated that the mechanism of BRG-1-mediated activation of ABCA1 involved interaction of LXR/RXR with BRG-1 and binding of this complex to ABCA1 promoter.Catalytic subunits of SWI/SNF chromatin remodeling complex, BRG-1 and brahma, play significant roles in enhancing LXR/RXR-mediated transcription of ABCA1 via the promoter DR-4 element.
Abstract Non-human primates, such as rhesus and cynomolgus monkey share a similar biochemistry and metabolism to humans. These animals are therefore crucial model systems in a number of areas of biomedical research. To simplify cytokine profiling we have developed a 28-plex magnetic luminex bead-based cytokine immunoassay for the analysis of rhesus and cynomolgus monkey samples. Validated sample types include serum, plasma, and conditioned tissue culture medium. Analytes include: EGF, eotaxin, FGF basic, G-CSF, GM-CSF, HGF, IFN-γ, IL-1β, IL-1RA, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12 p40/p70, IL-15, IL-17, I-TAC, MDC, MIF, MIG, MIP-1α, MIP-1β, MCP-1, RANTES, TNF-α, and VEGF. The utility of the assay is demonstrated by determining cytokine profiles obtained with LPS-stimulated or PMA plus A23187-stimulated peripheral blood mononuclear cells (PBMCs) from rhesus monkeys and cynomolgus monkeys. Linearity of dilution experiments with tissue culture medium and serum produce R2 values of 0.98 and greater, while sample recovery routinely falls between 80 and 120%. Intra-assay and inter-assay precision is ≤10% CV. This multiplex monkey cytokine assay provides a very powerful tool for addressing cytokine profiling in non-human primates. 28 cytokines can be simultaneously analyzed from a single sample greatly simplifying and cutting cost of monkey cytokine analysis.
The cytoplasmic domain of the beta subunit of the alpha IIb beta 3 integrin is required for cell spreading on fibrinogen. Here we report that deletion of six amino acids from the COOH terminus of the beta 3 (I757TYRGT) totally abolished cell spreading and formation of adhesion plaques, whereas retaining Ile757 partially preserved these functions. We further found that substitution of Tyr747 with Ala also abolished alpha IIb beta a-mediated cell spreading. The effects of these and other mutations on additional functions of alpha IIb beta 3 were also studied. Progressive truncations of beta 3, in which stop codons were inserted at amino acid positions 759-756, caused partial defects in the recruitment of alpha IIb beta 3 to preestablished adhesion plaques and a gradual decrease in the ability of alpha IIb beta 3 to mediate internalization of fibrinogen-coated particles. The Tyr747-->Ala substitution mutant was almost totally inactive in both of these assays. Point mutations at Tyr759, and at a conserved area close to the transmembrane domain of beta 3, decreased integrin recruitment to preestablished adhesion plaques but allowed alpha IIb beta 3-mediated formation of these structures and partial cell spreading. Deletion of the cytoplasmic domain of beta 3 did not affect the constitutive endocytosis of alpha IIb beta 3.
The plasma phospholipid transfer protein (PLTP) is an important regulator of high density lipoprotein (HDL) metabolism. We have here, based on sequence alignments of the plasma LPS-binding/lipid transfer protein family and the X-ray structure of the bactericidal/permeability increasing protein (BPI), modeled the structure of PLTP. The model predicts a two-domain architecture with conserved lipid-binding pockets consisting of apolar residues in each domain. By site-directed mutagenesis of selected amino acid residues and transient expression of the protein variants in HeLa cells, the pockets are shown to be essential for PLTP-mediated phospholipid transfer. A solid phase ligand binding assay was used to determine the HDL-binding ability of the mutants. The results suggest that the observed decreases in phospholipid transfer activity of the N-terminal pocket mutants cannot be attributed to altered HDL-binding, but the C-terminal lipid-binding pocket may be involved in the association of PLTP with HDL. Further, the essential structural role of a disulfide bridge between cysteine residues 146 and 185 is demonstrated. The structural model and the mutants characterized here provide powerful tools for the detailed analysis of the mechanisms of PLTP function.—Huuskonen, J., G. Wohlfahrt, M. Jauhiainen, C. Ehnholm, O. Teleman, and V. M. Olkkonen. Structure and phospholipid transfer activity of human PLTP: analysis by molecular modeling and site-directed mutagenesis. J. Lipid Res. 1999. 40: 1123–1130.
Amyloid beta A4 protein (APP) functions as a cell surface receptor and performs physiological functions on the surface of neurons relevant to neurite growth, neuronal adhesion and axonogenesis. It also influences cell mobility and transcription regulation through protein-protein interactions. Beta-amyloid peptides are small 36-43 amino acid peptides formed by proteolytic cleavage of the APP protein. These lipophilic metal chelators are the main components of amyloid plaques in the brains of Alzheimer's disease patients. Beta-amyloid peptides bind to lipoproteins and apolipoproteins E and J in the cerebrospinal fluid (CSF) and to HDL particles in plasma, inhibiting metal-catalyzed oxidation of lipoproteins. The most common forms of the Abeta peptides are Abeta40 and Abeta 42. Abeta40 is more commonly found but the more fibrillogenic Abeta42 is associated with the disease states. Measuring both Abeta40 and 42 peptide concentrations reliably is important from both the clinical as well as drug development point of view. Life Technologies is launching two new ELISA kits for accurate quantification of these markers. The kits are based on sandwich ELISA principle having two specific antibodies for these targets. These kits utilize very sensitive chemiluminescent detection method for increased dynamic range and sensitivity of the assays. Linear range of the assays goes up to 10 000 pg/ml making these kits very user friendly. The ELISA kits are capable of detecting both amyloid peptides in tissue culture medium as well as CSF. Extensive validation of these kits include linearity of dilution (accurate measurement of natural samples over a wide range), parallelism of standard curve and natural sample, accurate recovery of peptides from natural samples, tight inter- and intra-assay precision, as well as sensitivity (down to ∼1 pg/ml of either analyte). Overall these novel immunoassays provide an accurate method for quantification of beta-amyloid peptides in relevant biological matrixes.
We have developed a simple and robust probe-free quantitative PCR (qPCR) assay method that can detect minor mutant alleles with a frequency as low as 0.1% in a heterogeneous sample by introducing a novel T-blocker concept to the allele-specific PCR method. Four new KRAS and BRAF mutation detection assays were developed and their performance was demonstrated by testing a large number of replicates, utilizing a customized PCR protocol. Highly efficient and specific mutant amplification in conjunction with selective wild-type suppression by the T-blocker concept enabled 0.1% detection sensitivity using the intercalating dye-based qPCR chemistry instead of more complex target-specific dye-labeled probes. Excellent consistency in sensitivity and specificity of the T-blocker assay concept was demonstrated.
