H. C. Harsha

Vesiclepedia: A Compendium for Extracellular Vesicles with Continuous Community Annotation

Vesiclepedia is a community-annotated compendium of molecular data on extracellular vesicles.

Human protein reference database as a discovery resource for proteomics

The rapid pace at which genomic and proteomic data is being generated necessitates the development of tools and resources for managing data that allow integration of information from disparate sources. The Human Protein Reference Database (http://www.hprd.org) is a web-based resource based on open source technologies for protein information about several aspects of human proteins including protein-protein interactions, post-translational modifications, enzyme-substrate relationships and disease associations. This information was derived manually by a critical reading of the published literature by expert biologists and through bioinformatics analyses of the protein sequence. This database will assist in biomedical discoveries by serving as a resource of genomic and proteomic information and providing an integrated view of sequence, structure, function and protein networks in health and disease.

Plasma Proteome Database as a resource for proteomics research: 2014 update.

Plasma Proteome Database (PPD; http://www.plasmaproteomedatabase.org/) was initially described in the year 2005 as a part of Human Proteome Organization’s (HUPO’s) pilot initiative on Human Plasma Proteome Project. Since then, improvements in proteomic technologies and increased throughput have led to identification of a large number of novel plasma proteins. To keep up with this increase in data, we have significantly enriched the proteomic information in PPD. This database currently contains information on 10 546 proteins detected in serum/plasma of which 3784 have been reported in two or more studies. The latest version of the database also incorporates mass spectrometry-derived data including experimentally verified proteotypic peptides used for multiple reaction monitoring assays. Other novel features include published plasma/serum concentrations for 1278 proteins along with a separate category of plasma-derived extracellular vesicle proteins. As plasma proteins have become a major thrust in the field of biomarkers, we have enabled a batch-based query designated Plasma Proteome Explorer, which will permit the users in screening a list of proteins or peptides against known plasma proteins to assess novelty of their data set. We believe that PPD will facilitate both clinical and basic research by serving as a comprehensive reference of plasma proteins in humans and accelerate biomarker discovery and translation efforts.

Phosphoproteomics in cancer

Reversible protein phosphorylation serves as a basis for regulating a number of cellular processes. Aberrant activation of kinase signaling pathways is commonly associated with several cancers. Recent developments in phosphoprotein/phosphopeptide enrichment strategies and quantitative mass spectrometry have resulted in robust pipelines for high‐throughput characterization of phosphorylation in a global fashion. Today, it is possible to profile site‐specific phosphorylation events on thousands of proteins in a single experiment. The potential of this approach is already being realized to characterize signaling pathways that govern oncogenesis. In addition, chemical proteomic strategies have been used to unravel targets of kinase inhibitors, which are otherwise difficult to characterize. This review summarizes various approaches used for analysis of the phosphoproteome in general, and protein kinases in particular, highlighting key cancer phosphoproteomic studies.

A comprehensive map of the human urinary proteome.

The study of the human urinary proteome has the potential to offer significant insights into normal physiology as well as disease pathology. The information obtained from such studies could be applied to the diagnosis of various diseases. The high sensitivity, resolution, and mass accuracy of the latest generation of mass spectrometers provides an opportunity to accurately catalog the proteins present in human urine, including those present at low levels. To this end, we carried out a comprehensive analysis of human urinary proteome from healthy individuals using high-resolution Fourier transform mass spectrometry. Importantly, we used the Orbitrap for detecting ions in both MS (resolution 60 000) and MS/MS (resolution 15 000) modes. To increase the depth of our analysis, we characterized both unfractionated as well as lectin-enriched proteins in our experiments. In all, we identified 1,823 proteins with less than 1% false discovery rate, of which 671 proteins have not previously been reported as constituents of human urine. This data set should serve as a comprehensive reference list for future studies aimed at identification and characterization of urinary biomarkers for various diseases.

Proteogenomic Analysis of Mycobacterium tuberculosis By High Resolution Mass Spectrometry

The genome sequencing of H37Rv strain of Mycobacterium tuberculosis was completed in 1998 followed by the whole genome sequencing of a clinical isolate, CDC1551 in 2002. Since then, the genomic sequences of a number of other strains have become available making it one of the better studied pathogenic bacterial species at the genomic level. However, annotation of its genome remains challenging because of high GC content and dissimilarity to other model prokaryotes. To this end, we carried out an in-depth proteogenomic analysis of the M. tuberculosis H37Rv strain using Fourier transform mass spectrometry with high resolution at both MS and tandem MS levels. In all, we identified 3176 proteins from Mycobacterium tuberculosis representing ∼80% of its total predicted gene count. In addition to protein database search, we carried out a genome database search, which led to identification of ∼250 novel peptides. Based on these novel genome search-specific peptides, we discovered 41 novel protein coding genes in the H37Rv genome. Using peptide evidence and alternative gene prediction tools, we also corrected 79 gene models. Finally, mass spectrometric data from N terminus-derived peptides confirmed 727 existing annotations for translational start sites while correcting those for 33 proteins. We report creation of a high confidence set of protein coding regions in Mycobacterium tuberculosis genome obtained by high resolution tandem mass-spectrometry at both precursor and fragment detection steps for the first time. This proteogenomic approach should be generally applicable to other organisms whose genomes have already been sequenced for obtaining a more accurate catalogue of protein-coding genes.

Human Protein Reference Database and Human Proteinpedia as resources for phosphoproteome analysis

Human Protein Reference Database (HPRD) is a rich resource of experimentally proven features of human proteins. Protein information in HPRD includes protein-protein interactions, post-translational modifications, enzyme/substrate relationships, disease associations, tissue expression, and subcellular localization of human proteins. Although, protein-protein interaction data from HPRD has been widely used by the scientific community, its phosphoproteome data has not been exploited to its full potential. HPRD is one of the largest documentations of human phosphoproteins in the public domain. Currently, phosphorylation data in HPRD comprises of 95,016 phosphosites mapped on to 13,041 proteins. Additionally, enzyme-substrate reactions responsible for 5930 phosphorylation events were also documented. Significant improvements in technologies and high-throughput platforms in biomedical investigations led to an exponential increase of biological data and phosphoproteomic data in recent years. Human Proteinpedia, a community annotation portal developed by us, has also contributed to the significant increase in phosphoproteomic data in HPRD. A large number of phosphorylation events have been mapped on to reference sequences available in HPRD and Human Proteinpedia along with associated protein features. This will provide a platform for systems biology approaches to determine the role of protein phosphorylation in protein function, cell signaling, biological processes and their implication in human diseases. This review aims to provide a composite view of phosphoproteomic data pertaining to human proteins in HPRD and Human Proteinpedia.

Quantitative tissue proteomics of esophageal squamous cell carcinoma for novel biomarker discovery

Esophageal squamous cell carcinoma (ESCC) is among the top ten most frequent malignancies worldwide. In this study, our objective was to identify potential biomarkers for ESCC through a quantitative proteomic approach using the isobaric tags for relative and absolute quantitation (iTRAQ) approach. We compared the protein expression profiles of ESCC tumor tissues with the corresponding adjacent normal tissue from ten patients. LC-MS/MS analysis of strong cation exchange chromatography fractions was carried out on an Accurate Mass QTOF mass spectrometer, which led to the identification of 687 proteins. In all, 257 proteins were identified as differentially expressed in ESCC as compared to normal. We found several previously known protein biomarkers to be upregulated in ESCC including thrombospondin 1 (THBS1), periostin 1 (POSTN) and heat shock 70 kDa protein 9 (HSPA9) confirming the validity of our approach. In addition, several novel proteins that had not been reported previously were identified in our screen. These novel biomarker candidates included prosaposin (PSAP), plectin 1 (PLEC1) and protein disulfide isomerase A 4 (PDIA4) that were further validated to be overexpressed by immunohistochemical labeling using tissue microarrays. The success of our study shows that this mass spectrometric strategy can be applied to cancers in general to develop a panel of candidate biomarkers, which can then be validated by other techniques.

SILAC-based quantitative proteomic approach to identify potential biomarkers from the esophageal squamous cell carcinoma secretome

The identification of secreted proteins that are differentially expressed between non-neoplastic and esophageal squamous cell carcinoma (ESCC) cells can provide potential biomarkers of ESCC. We used a SILAC-based quantitative proteomic approach to compare the secretome of ESCC cells with that of non-neoplastic esophageal squamous epithelial cells. Proteins were resolved by SDS-PAGE, and tandem mass spectrometry analysis (LC-MS/MS) of in-gel trypsin-digested peptides was carried out on a high-accuracy qTOF mass spectrometer. In total, we identified 441 proteins in the combined secretomes, including 120 proteins with >2-fold upregulation in the ESCC secretome vs. that of non-neoplastic esophageal squamous epithelial cells. In this study, several potential protein biomarkers previously known to be increased in ESCC including matrix metalloproteinase 1, transferrin receptor, and transforming growth factor beta-induced 68 kDa were identified as overexpressed in the ESCC-derived secretome. In addition, we identified several novel proteins that have not been previously reported to be associated with ESCC. Among the novel candidate proteins identified, protein disulfide isomerase family a member 3 (PDIA3), GDP dissociation inhibitor 2 (GDI2), and lectin galactoside binding soluble 3 binding protein (LGALS3BP) were further validated by immunoblot analysis and immunohistochemical labeling using tissue microarrays. This tissue microarray analysis showed overexpression of protein disulfide isomerase family a member 3, GDP dissociation inhibitor 2, and lectin galactoside binding soluble 3 binding protein in 93%, 93% and 87% of 137 ESCC cases, respectively. Hence, we conclude that these potential biomarkers are excellent candidates for further evaluation to test their role and efficacy in the early detection of ESCC.

LC-MS/MS Analysis of Differentially Expressed Glioblastoma Membrane Proteome Reveals Altered Calcium Signaling and Other Protein Groups of Regulatory Functions

Membrane proteins play key roles in the development and progression of cancer. We have studied differentially expressed membrane proteins in glioblastoma multiforme (GBM), the most common and aggressive type of primary brain tumor, by high resolution LC-MS/MS mass spectrometry and quantitation by iTRAQ. A total of 1834 membrane proteins were identified with high confidence, of which 356 proteins were found to be altered by 2-fold change or more (198 up- and 158 down-regulated); 56% of them are known membrane proteins associated with major cellular processes. Mass spectrometry results were confirmed for representative proteins on individual specimens by immunohistochemistry. On mapping of the differentially expressed proteins to cellular pathways and functional networks, we notably observed many calcium-binding proteins to be altered, implicating deregulation of calcium signaling and homeostasis in GBM, a pathway also found to be enriched in the report (Dong, H., Luo, L., Hong, S., Siu, H., Xiao, Y., Jin, L., Chen, R., and Xiong, M. (2010) Integrated analysis of mutations, miRNA and mRNA expression in glioblastoma. BMC Syst. Biol. 4, 163) based on The Cancer Genome Atlas analysis of GBMs. Annotations of the 356 proteins identified by us with The Cancer Genome Atlas transcriptome data set indicated overlap with 295 corresponding transcripts, which included 49 potential miRNA targets; many transcripts correlated with proteins in their expression status. Nearly 50% of the differentially expressed proteins could be classified as transmembrane domain or signal sequence-containing proteins (159 of 356) with potential of appearance in cerebrospinal fluid or plasma. Interestingly, 75 of them have been already reported in normal cerebrospinal fluid or plasma along with other proteins. This first, in-depth analysis of the differentially expressed membrane proteome of GBM confirms genes/proteins that have been implicated in earlier studies, as well as reveals novel candidates that are being reported for the first time in GBM or any other cancer that could be investigated further for clinical applications.