A Proteomic Analysis of the Malignant Mesothelioma Secretome Using iTRAQ

Our plain-English summary of A Proteomic Analysis of the Malignant Mesothelioma Secretome Using iTRAQ, by J. Creaney, I.M. Dick, J.S. Leon, et al (Cancer Genomics & Proteomics, 2017).

The study

• Authors: J. Creaney, I.M. Dick, J.S. Leon, B.W. Robinson
• Journal: Cancer Genomics & Proteomics
• Published: 2017;14(2):103-117
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Unlabelled: Backgound/Aim: Malignant mesothelioma (MM) is an aggressive and fatal pleural cancer. The cell secretome offers information allowing insight into the pathogenesis of MM while offering the possibility to identify potential therapeutic targets and biomarkers. In the present study the secretome protein profile of MM cell lines was compared to normal mesothelial cells.

Materials And Methods: Six MM cell lines were compared against three primary mesothelial cell culture preparations using iTRAQ® mass spectrometry.

Results: MM cell lines more abundantly secreted exosome-associated proteins than mesothelial cells. MM cell secretomes were enriched in proteins that are involved in response to stress, carbon metabolism, biosynthesis of amino acids, antigen processing and presentation and protein processing in the endoplasmic reticulum.

Conclusion: The MM cell secretome is enriched in proteins that are likely to enhance its growth and response to stress and help it inhibit an adaptive immune response. These are potential targets for therapeutic and biomarker discovery.

Copyright© 2017, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.

In plain English

This laboratory study used cultured cells derived from patients; it did not examine asbestos exposure or patients' health. The authors used iTRAQ mass spectrometry to compare proteins released into culture fluid (the 'secretome') by six malignant mesothelioma cell lines and three short-term normal mesothelial cell cultures. The normal cells came from pericardial fluid of coronary artery bypass patients. Of 572 proteins identified across three experiments, 177 found in all experiments were analysed further. A group of 47 proteins was generally more abundant in the mesothelioma secretomes, and a group of 46 less abundant. Proteins in the more abundant group were more often classified as secreted only by non-classical mechanisms, meaning no signal peptide was present (62% vs. 36%, p=0.009). That group was enriched in proteins linked to carbon and amino acid metabolism, antigen processing and presenting, and protein processing. The authors concluded that the mesothelioma secretome is highly enriched in proteins secreted in exosomes (small membrane-bound sacs), and suggested it may help the tumour evade an adaptive immune response. They noted their method may have missed some proteins.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) proteomic study comparing proteins secreted by malignant mesothelioma cell lines and normal mesothelial cell cultures, using iTRAQ mass spectrometry in three independent experiments
• Who was studied: Six previously established malignant mesothelioma cell lines (JU77, LO68, ONE58, OLD1612, JO38, GAY2911), derived from male patients aged 48 to 70 at diagnosis with epithelioid or biphasic histology. Controls were three short-term cultures of normal mesothelial cells from pericardial fluid of patients undergoing coronary artery bypass operations: a 74-year-old man, a 45-year-old man and a 54-year-old woman. The work was done in Perth, Western Australia.
• Exposure: No asbestos exposure was studied. The comparison was between proteins secreted by malignant mesothelioma cell lines and by normal mesothelial cells grown for 24 hours in serum-free media.
• Main results:
  • In total, 572 proteins were identified across the three experiments. Of these, 177 were identified in every mesothelioma cell line at least once and in all three experiments, and these were analysed further.
  • Of the 177 commonly detected proteins, 168 (95%) had been previously identified in cancer secretomes.
  • One cluster (Group 2) of 47 proteins (26% of the total) was in general over-expressed in the mesothelioma cell lines relative to the normal mesothelial cultures.
  • Another cluster (Group 4) of 46 proteins (25% of the total) consisted predominantly of proteins less abundantly expressed across the mesothelioma cell lines.
  • Proteins in the over-expressed Group 2 were more often classified than those in the under-expressed Group 4 as secreted only by non-classical mechanisms, meaning no signal peptide was present (62% vs. 36%, Pearson's Chi-square 6.75, p=0.009). The classification was based on secretion-prediction scores (SignalP and SecretomeP).
  • The over-expressed Group 2 was enriched in carbon and amino acid metabolism, antigen processing and presenting, glycolysis/gluconeogenesis, and protein processing pathways.
  • Of the 177 secretome proteins, 71 (40%) were also present in mesothelioma exosome preparations reported in the authors' earlier study.
  • In the exosomes of the four mesothelioma cell lines, 19 of 47 (40%) Group 2 proteins were found, compared with 10 of 46 (22%) Group 4 proteins. The p-value for this difference was 0.051, above the study's p<0.05 threshold for statistical significance.
• The authors' conclusion: The authors concluded that the mesothelioma cell secretome is highly enriched in proteins secreted in exosomes. They found it characterized by increased secretion of proteins associated with stress response, growth-related metabolism and metastasis, and by decreased proteins associated with cell senescence. They suggested the secretome assists mesothelioma in evading an adaptive immune response.
• Limitations the authors state:
  • The data-dependent acquisition mass spectrometry approach may have missed relevant secreted proteins. Low-abundance peptides were detected only randomly, with a consequent lack of reproducibility.

Topics

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Biomarker, Mesothelial Cells, Discovery.

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• Comparative proteomics and pulmonary toxicity of instilled single-walled carbon nanotubes, crocidolite asbestos, and ultrafine carbon black in mice — J.G. Teeguarden, B.J. Webb-Robertson, et al. (2011)
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• Secreted primary human malignant mesothelioma exosome signature reflects oncogenic cargo — D.W. Greening, H. Ji, et al. (2016)

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