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1.  A multiplex targeted proteomic assay for biomarker detection in plasma: a pancreatic cancer biomarker case study 
Journal of Proteome Research  2012;11(3):1937-1948.
Biomarkers are most frequently proteins that are measured in the blood. Their development largely relies on antibody creation to test the protein candidate performance in blood samples of diseased versus non-diseased patients. The creation of such antibody assays has been a bottleneck in biomarker progress due to the cost, extensive time and effort required to complete the task. Targeted proteomics is an emerging technology that is playing an increasingly important role to facilitate disease biomarker development. In this study, we applied a SRM-based targeted proteomics platform to directly detect candidate biomarker proteins in plasma to evaluate their clinical utility for pancreatic cancer detection. The characterization of these protein candidates used a clinically well-characterized cohort that included plasma samples from patients with pancreatic cancer, chronic pancreatitis and healthy age-matched controls. Three of the five candidate proteins, including gelsolin, lumican and tissue inhibitor of metalloproteinase 1, demonstrated an AUC value greater than 0.75 in distinguishing pancreatic cancer from the controls. In addition, we provide an analysis of the reproducibility, accuracy, and robustness of the SRM-based proteomics platform. This information addresses important technical issues that could aid in the adoption of the targeted proteomics platform for practical clinical utility.
doi:10.1021/pr201117w
PMCID: PMC3292708  PMID: 22316387
Targeted proteomics; Mass spectrometer; Selected reaction monitoring (SRM); Multiple reaction monitoring (MRM); Pancreas; Pancreatic ductal adenocarcinoma; Pancreatic cancer; Chronic pancreatitis; Biomarker; Plasma
2.  A targeted proteomics–based pipeline for verification of biomarkers in plasma 
Nature biotechnology  2011;29(7):625-634.
High-throughput technologies can now identify hundreds of candidate protein biomarkers for any disease with relative ease. However, because there are no assays for the majority of proteins and de novo immunoassay development is prohibitively expensive, few candidate biomarkers are tested in clinical studies. We tested whether the analytical performance of a biomarker identification pipeline based on targeted mass spectrometry would be sufficient for data-dependent prioritization of candidate biomarkers, de novo development of assays and multiplexed biomarker verification. We used a data-dependent triage process to prioritize a subset of putative plasma biomarkers from >1,000 candidates previously identified using a mouse model of breast cancer. Eighty-eight novel quantitative assays based on selected reaction monitoring mass spectrometry were developed, multiplexed and evaluated in 80 plasma samples. Thirty-six proteins were verified as being elevated in the plasma of tumor-bearing animals. The analytical performance of this pipeline suggests that it should support the use of an analogous approach with human samples.
doi:10.1038/nbt.1900
PMCID: PMC3232032  PMID: 21685906
3.  Dynamic changes in histone acetylation regulate origins of DNA replication 
While histone modifications have been implicated in many DNA-dependent processes, their precise role in DNA replication remains largely unknown. Here, we describe a very efficient, single-step method to specifically purify histones located around an origin of replication from S. cerevisiae. Using high-resolution mass spectrometry, we have obtained a comprehensive view of the histone modifications surrounding the origin of replication throughout the cell cycle. We have discovered that histone H3 and H4 acetylation is dynamically regulated around an origin of replication, at the level of multiply-acetylated histones. Furthermore, we find that this acetylation is required for efficient origin activation during S-phase.
doi:10.1038/nsmb.1780
PMCID: PMC3060656  PMID: 20228802
DNA replication; histone modifications; mass spectrometry
4.  Ubiquitin-proteasome mediated synaptic reorganization - a novel mechanism underlying rapid ischemic tolerance 
Ischemic tolerance is an endogenous neuroprotective mechanism in brain and other organs, whereby prior exposure to brief ischemia produces resilience to subsequent normally injurious ischemia. While many molecular mechanisms mediate delayed (gene-mediated) ischemic tolerance, the mechanisms underlying rapid (protein synthesis independent) ischemic tolerance are relatively unknown. Here we describe a novel mechanism for the induction of rapid ischemic tolerance mediated by the ubiquitin-proteasome system. Rapid ischemic tolerance is blocked by multiple proteasome inhibitors (MG132, MG115 and clasto-lactacystin β-lactone). A proteomics strategy was used to identify ubiquitinated proteins following preconditioning ischemia. We focused our studies on two actin binding proteins of the post synaptic density that were ubiquitinated following rapid preconditioning: myristoylated, alanine-rich C-kinase substrate (MARCKS) and fascin. Immunoblots confirm the degradation of MARCKS and fascin following preconditioning ischemia. The loss of actin binding proteins promotes actin reorganization in the post synaptic density and transient retraction of dendritic spines. This rapid and reversible synaptic remodeling reduces NMDA-mediated electrophysiological responses and renders the cells refractory to NMDA receptor-mediated toxicity. The dendritic spine retraction and NMDA-neuroprotection following preconditioning ischemia are blocked by actin stabilization with jasplakinolide, as well as proteasome inhibition with MG132. Taken together these data suggest that rapid tolerance results from changes to the post-synaptic density mediated by the ubiquitin-proteasome system, rendering neurons resistant to excitotoxicity.
doi:10.1523/JNEUROSCI.3474-07.2008
PMCID: PMC2946223  PMID: 18171922
Ischemia; Actin; NMDA; Proteasome; dendritic spines; ubiquitin
5.  Proteomic analysis of native metabotropic glutamate receptor 5 protein complexes reveals novel molecular constituents 
Journal of neurochemistry  2004;91(2):438-450.
We used a proteomic approach to identify novel proteins that may regulate metabotropic glutamate receptor 5 (mGluR5) responses by direct or indirect protein interactions. This approach does not rely on the heterologous expression of proteins and offers the advantage of identifying protein interactions in a native environment. The mGluR5 protein was immunoprecipitated from rat brain lysates; co-immunoprecipitating proteins were analyzed by mass spectrometry and identified peptides were matched to protein databases to determine the correlating parent proteins. This proteomic approach revealed the interaction of mGluR5 with known regulatory proteins, as well as novel proteins that reflect previously unidentified molecular constituents of the mGluR5-signaling complex. Immunoblot analysis confirmed the interaction of high confidence proteins, such as phosphofurin acidic cluster sorting protein 1, microtubule-associated protein 2a and dynamin 1, as mGluR5-interacting proteins. These studies show that a proteomic approach can be used to identify candidate interacting proteins. This approach may be particularly useful for neurobiology applications where distinct protein interactions within a signaling complex can dramatically alter the outcome of the response to neurotransmitter release, or the disruption of normal protein interactions can lead to severe neurological and psychiatric disorders.
doi:10.1111/j.1471-4159.2004.02735.x
PMCID: PMC2747775  PMID: 15447677
mass spectrometry; metabotropic glutamate receptor; protein interaction; proteomics
6.  The Standard Protein Mix Database: A Diverse Dataset to Assist in the Production of Improved Peptide and Protein Identification Software Tools 
Journal of proteome research  2007;7(1):96-103.
Tandem mass spectrometry (MS/MS) is frequently used in the identification of peptides and proteins. Typical proteomic experiments rely on algorithms such as SEQUEST and MASCOT to compare thousands of tandem mass spectra against the theoretical fragment ion spectra of peptides in a database. The probabilities that these spectrum-to-sequence assignments are correct can be determined by statistical software such as PeptideProphet or through estimations based on reverse or decoy databases. However, many of the software applications that assign probabilities for MS/MS spectra to sequence matches were developed using training datasets from 3D ion-trap mass spectrometers. Given the variety of types of mass spectrometers that have become commercially available over the last five years, we sought to generate a dataset of reference data covering multiple instrumentation platforms to facilitate both the refinement of existing computational approaches and the development of novel software tools. We analyzed the proteolytic peptides in a mixture of tryptic digests of 18 proteins, named the “ISB standard protein mix”, using 8 different mass spectrometers. These include linear and 3D ion traps, two quadrupole time-of-flight platforms (qq-TOF) and two MALDI-TOF-TOF platforms. The resulting dataset, which has been named the Standard Protein Mix Database, consists of over 1.1 million spectra in 150+ replicate runs on the mass spectrometers. The data were inspected for quality of separation and searched using SEQUEST. All data, including the native raw instrument and mzXML formats and the PeptideProphet validated peptide assignments, are available at http://regis-web.systemsbiology.net/PublicDatasets/.
doi:10.1021/pr070244j
PMCID: PMC2577160  PMID: 17711323
Proteomics; reference dataset; database search software; standard protein mix; Standard Protein Mix Database
7.  Phosphorylation at S365 is a gatekeeper event that changes the structure of Cx43 and prevents down-regulation by PKC 
The Journal of Cell Biology  2007;179(6):1301-1309.
Phosphorylation at unspecified sites is known to regulate the life cycle (assembly, gating, and turnover) of the gap junction protein, Cx43. In this paper, we show that Cx43 is phosphorylated on S365 in cultured cells and heart tissue. Nuclear magnetic resonance structural studies of the C-terminal region of Cx43 with an S365D mutation indicate that it forms a different stable conformation than unphosphorylated wild-type Cx43. Immunolabeling with an antibody specific for Cx43 phosphorylated at S365 shows staining on gap junction structures in heart tissue that is lost upon hypoxia when Cx43 is no longer specifically localized to the intercalated disk. Efficient phosphorylation at S368, an important Cx43 channel regulatory event that increases during ischemia or PKC activation, depends on S365 being unphosphorylated. Thus, phosphorylation at S365 can serve a “gatekeeper” function that may represent a mechanism to protect cells from ischemia and phorbol ester-induced down-regulation of channel conductance.
doi:10.1083/jcb.200707060
PMCID: PMC2140020  PMID: 18086922
8.  Comparison of ESI MS Interfaces for the Analysis of UV-crosslinked Peptide-Nucleic Acid Complexes 
In this report, the effectiveness of high performance liquid chromatography (HPLC) in conjunction with electrospray ionization mass spectrometry (ESI-MS) is examined as a tool for identifying the sites of crosslinking in a protein that has been photoreacted with a non-photolabeled oligonucleotide. ESI-MS and MALDI-MS analyses preceded by off-line microflow and nanoflow HPLC, on-line microflow HPLC/ESI, and on-line nanoflow HPLC/ESI interfaces were performed in order to determine their relative effectiveness in separating mixtures of nucleopeptides and identifying sites of crosslinking on the individual components. The characteristics of these four techniques as well as possibilities for improving the analysis of nucleopeptides by ESI MS are compared and discussed.
doi:10.1016/j.jchromb.2007.09.029
PMCID: PMC2238692  PMID: 18042442
9.  Methodologies for Characterizing Phosphoproteins by Mass Spectrometry 
Cell communication & adhesion  2006;13(5-6):249-262.
doi:10.1080/15419060601077917
PMCID: PMC2185548  PMID: 17162667
Phosphorylation; Mass spectrometry; Kinase; Sequencing
10.  NFX1-123 and Poly(A) Binding Proteins Synergistically Augment Activation of Telomerase in Human Papillomavirus Type 16 E6-Expressing Cells▿  
Journal of Virology  2007;81(8):3786-3796.
Overcoming senescence signals in somatic cells is critical to cellular immortalization and carcinogenesis. High-risk human papillomavirus (HPV) can immortalize epithelial cells in culture through degradation of the retinoblastoma protein by HPV E7 and activation of hTERT transcription, the catalytic subunit of telomerase, by the heterodimer HPV E6/E6-associated protein (E6AP). Recent work in our laboratory identified a novel repressor of hTERT transcription, NFX1-91, which is targeted for ubiquitin-mediated degradation by HPV type 16 (HPV16) E6/E6AP. In contrast, NFX1-123, a splice variant NFX1, increased expression from an hTERT promoter that was activated by HPV16 E6/E6AP. Here, we show that HPV16 E6 bound both NFX1-91 and NFX1-123 through the common central domain of NFX1 in the absence of E6AP. NFX1-123 positively regulated hTERT expression, as its knockdown decreased hTERT mRNA levels and telomerase activity and its overexpression increased telomerase activity. We identified new protein partners of NFX1-123, including several cytoplasmic poly(A) binding proteins (PABPCs) that interacted with NFX1-123 through its N-terminal PAM2 motif, a protein domain characteristic of other PABPC protein partners. Furthermore, NFX1-123 and PABPCs together had a synergistic stimulatory effect on hTERT-regulated reporter assays. The data suggest that NFX1-123 is integral to hTERT regulation in HPV16 E6-expressing epithelial cells and that the interaction between NFX1-123 and PABPCs is critical to hTERT activity.
doi:10.1128/JVI.02007-06
PMCID: PMC1866132  PMID: 17267499

Results 1-10 (10)