A matrix-assisted laser desorption ionization-time-of-flight-time-of-flight-mass spectrometry-based toxicoproteomic screening method to assess in vitro particle potencies

Knowledge of biological reactivity and underlying toxicity mechanisms of airborne particulate matter (PM) is central to the characterization of the risk associated with these pollutants. An integrated screening platform consisting of protein profiling of cellular responses and cytotoxic analysis was developed in this study for the estimation of PM potencies. Mouse macrophage (J774A.1) and human lung epithelial cells (A549) were exposed in vitro to Ottawa urban particles (EHC6802) and two reference mineral particles (TiO₂ and SiO₂). Samples from the in vitro exposure experiment were tested following an integrated classical cytotoxicity/toxicoproteomic assessment approach for cellular viability (CellTiter Blue®, lactate dehydrogenase) and proteomic analyses. Cellular proteins were pre‐fractionated by molecular weight cut‐off filtration, digested enzymatically and were analyzed by matrix‐assisted laser desorption ionization–time‐of‐flight–time‐of‐flight–mass spectrometry for protein profiling and identification. Optimization of detergent removal, pre‐fractionation strategies and enzymatic digestion procedures led to increased tryptic peptide (m/z) signals with reduced sample processing times, for small total protein contents. Proteomic analyses using this optimized procedure identified statistically significant (P < 0.05) PM dose‐dependent changes at the molecular level. Ranking of PM potencies based on toxicoproteomic analysis were in line with classical cytotoxicity potency‐based ranking. The high content toxicoproteomic approach exhibited the potential to add value to risk characterization of environmental PM exposures by complementing and validating existing cytotoxicity testing strategies.

To estimate in vitro potencies of ambient air particles we developed an integrated screening platform that enabled protein profiling of cellular responses and cytotoxic analyses. Extensive optimization of the toxicoproteomic analysis was carried out. Cellular proteomic changes were consistent with cytotoxicity findings. The integration of proteomic and cytotoxicity analyses results provided insight into particulate matter cytotoxic reactivity‐related mechanistic information at the molecular level.

Human lung epithelial cell A549 proteome data after treatment with titanium dioxide and carbon black

Here, we have described the dataset relevant to the A549 cellular proteome changes after exposure to either titanium dioxide or carbon black particles as compared to the non-exposed controls, “Proteomic changes in human lung epithelial cells (A549) in response to carbon black and titanium dioxide exposures” (Vuong et al., 2016) [1]. Detailed methodologies on the separation of cellular proteins by 2D-GE and the subsequent mass spectrometry analyses using MALDI-TOF-TOF-MS are documented. Particle exposure-specific protein expression changes were measured via 2D-GE spot volume analysis. Protein identification was done by querying mass spectrometry data against SwissProt and RefSeq protein databases using Mascot search engine. Two-way ANOVA analysis data provided information on statistically significant A549 protein expression changes associated with particle exposures.

Discovery of substrates for a SET domain lysine methyltransferase predicted by multistate computational protein design

Characterization of lysine methylation has proven challenging despite its importance in biological processes such as gene transcription, protein turnover, and cytoskeletal organization. In contrast to other key posttranslational modifications, current proteomics techniques have thus far shown limited success at characterizing methyl-lysine residues across the cellular landscape. To complement current biochemical characterization methods, we developed a multistate computational protein design procedure to probe the substrate specificity of the protein lysine methyltransferase SMYD2. Modeling of substrate-bound SMYD2 identified residues important for substrate recognition and predicted amino acids necessary for methylation. Peptide- and protein- based substrate libraries confirmed that SMYD2 activity is dictated by the motif [LFM]-1-K(∗)-[AFYMSHRK]+1-[LYK]+2 around the target lysine K(∗). Comprehensive motif-based searches and mutational analysis further established four additional substrates of SMYD2. Our methodology paves the way to systematically predict and validate posttranslational modification sites while simultaneously pairing them with their associated enzymes.

Quantitative proteomic analysis of PCSK9 gain of function in human hepatic HuH7 cells

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in cholesterol homeostasis, mediating degradation of the liver low-density lipoprotein receptor (LDLR). In fact, gain- and loss-of-function PCSK9 variations in human populations associate with hyper- or hypo- cholesterolemia, respectively. Exactly how PCSK9 promotes degradation of the LDLR, the identity of the other biomolecules involved in this process, and the global effect of PCSK9 on other proteins has not been thoroughly studied. Here we employ stable isotope labeling with amino acids in cell culture (SILAC) to present the first quantitative, subcellular proteomic study of proteins affected by the stable overexpression of a gain-of-function PCSK9 membrane-bound chimera (PCSK9-V5-ACE2) in comparison to control, empty vector transfections in a human hepatocyte (HuH7) cell line. The expression level of 327 of 5790 peptides was modified by PCSK9-V5-ACE2 overexpression. Immunoblotting was carried out for the control transferrin receptor, shown to be unaffected in cells overexpressing PCSK9-V5-ACE2, thus validating our SILAC results. We also used immunoblotting to confirm the novel SILAC results of up- and down-regulation of several proteins in cells overexpressing PCSK9-V5-ACE2. Moreover, we documented the novel down-regulation of the EH domain binding protein-1 (EHBP1) in a transgenic PCSK9 mouse model and its up-regulation in a PCSK9 knockout mouse model.

Lipidomics era: accomplishments and challenges

Lipid mediators participate in signal transduction pathways, proliferation, apoptosis, and membrane trafficking in the cell. Lipids are highly complex and diverse owing to the various combinations of polar headgroups, fatty acyl chains, and backbone structures. This structural diversity continues to pose a challenge for lipid analysis. Here we review the current state of the art in lipidomics research and discuss the challenges facing this field. The latest technological developments in mass spectrometry, the role of bioinformatics, and the applications of lipidomics in lipid metabolism and cellular physiology and pathology are also discussed.

Rare cell proteomic reactor applied to stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomics study of human embryonic stem cell differentiation

The molecular basis governing the differentiation of human embryonic stem cells (hESCs) remains largely unknown. Systems-level analysis by proteomics provides a unique approach to tackle this question. However, the requirement of a large number of cells for proteomics analysis (i.e. 10(6)-10(7) cells) makes this assay challenging, especially for the study of rare events during hESCs lineage specification. Here, a fully integrated proteomics sample processing and analysis platform, termed rare cell proteomic reactor (RCPR), was developed for large scale quantitative proteomics analysis of hESCs with ∼50,000 cells. hESCs were completely extracted by a defined lysis buffer, and all of the proteomics sample processing procedures, including protein preconcentration, reduction, alkylation, and digestion, were integrated into one single capillary column with a strong cation exchange monolith matrix. Furthermore, on-line two-dimensional LC-MS/MS analysis was performed directly using RCPR as the first dimension strong cation exchange column. 2,281 unique proteins were identified on this system using only 50,000 hESCs. For stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative study, a ready-to-use and chemically defined medium and an in situ differentiation procedure were developed for complete SILAC labeling of hESCs with well characterized self-renewal and differentiation properties. Mesoderm-enriched differentiation was studied by RCPR using 50,000 hESCs, and 1,086 proteins were quantified with a minimum of two peptides per protein. Of these, 56 proteins exhibited significant changes during mesoderm-enriched differentiation, and eight proteins were demonstrated for the first time to be overexpressed during early mesoderm development. This work provides a new platform for the study of rare cells and in particular for further elucidating proteins that govern the mesoderm lineage specification of human pluripotent stem cells.

Analysis of the subcellular phosphoproteome using a novel phosphoproteomic reactor

Protein phosphorylation is an important post-translational modification involved in the regulation of many cellular processes. Mass spectrometry has been successfully used to identify protein phosphorylation in specific pathways and for global phosphoproteomic analysis. However, phosphoproteomics approaches do not evaluate the subcellular localization of the phosphorylated forms of proteins, which is an important factor for understanding the roles of protein phosphorylation on a global scale. The in-depth mapping of protein phosphorylation at the subcellular level necessitates the development of new methods capable of specifically and efficiently enriching phosphopeptides from highly complex samples. Here, we report a novel microfluidic device called the phosphoproteomic reactor that combines efficient processing of proteins followed by phosphopeptide enrichment by Ti-IMAC. To illustrate the potential of this novel technology, we mapped the phosphoproteins in subcellular organelles of liver cells. Fifteen subcellular fractions from liver cell cultures were processed on the phosphoproteomic reactor in combination with nano-LC-MS/MS analysis. We identified thousands of phosphorylation sites in over 600 phosphoproteins in different organelles using minute amounts of starting material. Overall, this approach provides a new avenue for studying the phosphoproteome of the subcellular organelles.

Identification of protein-protein interactions by mass spectrometry coupled techniques

The use of mass spectrometry in protein identification has revolutionized the field of proteomics. Coupled to various affinity purification techniques, mass spectrometry is used to identify protein-protein interactions. This chapter looks at the use of these affinity purification techniques in the identification of protein interactions. Various tags are used to purify protein complexes including tandem affinity purification. The FLAG tag is another commonly used tag which is a small tag that tends not to interfere with the protein function. These different affinity purification methods are used to purify proteins that are further identified by either ESI-MS or MALDI-MS.

The tale of two domains: proteomics and genomics analysis of SMYD2, a new histone methyltransferase

Very little is known about SET- and MYND-containing protein 2 (SMYD2), a member of the SMYD protein family. However, the interest in better understanding the roles of SMYD2 has grown because of recent reports indicating that SMYD2 methylates p53 and histone H3. In this study, we present a combined proteomics and genomics study of SMYD2 designed to elucidate its molecular roles. We report the cytosolic and nuclear interactome of SMYD2 using a combination of immunoprecipitation coupled with high throughput MS, chromatin immunoprecipitation coupled with high throughput MS, and co-immunoprecipitation methods. In particular, we report that SMYD2 interacted with HSP90alpha independently of the SET and MYND domains, with EBP41L3 through the MYND domain, and with p53 through the SET domain. We demonstrated that the interaction of SMYD2 with HSP90alpha enhances SMYD2 histone methyltransferase activity and specificity for histone H3 at lysine 4 (H3K4) in vitro. Interestingly histone H3K36 methyltransferase activity was independent of its interaction with HSP90alpha similar to LSD1 dependence on the androgen receptor. We also showed that the SET domain is required for the methylation at H3K4. We demonstrated using a modified chromatin immunoprecipitation protocol that the SMYD2 gain of function leads to an increase in H3K4 methylation in vivo, whereas no observable levels of H3K36 were detected. We also report that the SMYD2 gain of function was correlated with the up-regulation of 37 and down-regulation of four genes, the majority of which are involved in the cell cycle, chromatin remodeling, and transcriptional regulation. TACC2 is one of the genes up-regulated as a result of SMYD2 gain of function. Up-regulation of TACC2 by SMYD2 occurred as a result of SMYD2 binding to the TACC2 promoter where it methylates H3K4. Furthermore the combination of the SMYD2 interactome with the gene expression data suggests that some of the genes regulated by SMYD2 are closely associated with SMYD2-interacting proteins.

Large-scale mapping of human protein-protein interactions by mass spectrometry

Mapping protein–protein interactions is an invaluable tool for understanding protein function. Here, we report the first large-scale study of protein–protein interactions in human cells using a mass spectrometry-based approach. The study maps protein interactions for 338 bait proteins that were selected based on known or suspected disease and functional associations. Large-scale immunoprecipitation of Flag-tagged versions of these proteins followed by LC-ESI-MS/MS analysis resulted in the identification of 24 540 potential protein interactions. False positives and redundant hits were filtered out using empirical criteria and a calculated interaction confidence score, producing a data set of 6463 interactions between 2235 distinct proteins. This data set was further cross-validated using previously published and predicted human protein interactions. In-depth mining of the data set shows that it represents a valuable source of novel protein–protein interactions with relevance to human diseases. In addition, via our preliminary analysis, we report many novel protein interactions and pathway associations.

Evidence for cadmium uptake through Nramp2: metal speciation studies with Caco-2 cells

The specific uptake of 0.3 microM (109)Cd by the TC7 clone of the human enterocytic-like Caco-2 cells increased 4-fold as the pH(out) was lowered from 7.5 to 5.5; the stimulatory effect of acidic media being more pronounced when the level of the free ion (109)Cd(2+), relative to total (109)Cd, was increased. The initial uptake rate was 12-fold higher under conditions, optimizing (109)Cd(2+) accumulation over that of (109)CdCl(2-n)(n) (NO(-)(3)/pH(out) 5.5); a saturable system of transport has been characterized (K(m) = 1.1 +/- 0.1 microM, V(max) = 87 +/- 3 pmol/3 min/mg protein). An excess of Fe(2+) failed to affect (109)Cd uptake when the pH(out) was 7.4, whereas a strong inhibition was observed under NO(-)(3)/pH(out) 5.5 conditions. In contrast, the maximal inhibitory effect of Zn(2+) was observed under Cl(-)/pH(out) 7.4 conditions. This results strongly suggest that Fe(2+) may compete with Cd(2+) for Nramp2, whereas Zn and CdCl(2-n)(n) compete for another system of transport that has yet to be identified.