Distinct affinity of nuclear proteins to the surface of chrysotile and crocidolite

Our plain-English summary of Distinct affinity of nuclear proteins to the surface of chrysotile and crocidolite, by Y. Kubo, H. Takenaka, H. Nagai, et al (Journal of Clinical Biochemistry and Nutrition, 2012).

The study

• Authors: Y. Kubo, H. Takenaka, H. Nagai, S. Toyokuni
• Journal: Journal of Clinical Biochemistry and Nutrition
• Published: 2012;51(3):221-6
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The inhalation of asbestos is a risk factor for the development of malignant mesothelioma and lung cancer. Based on the broad surface area of asbestos fibers and their ability to enter the cytoplasm and nuclei of cells, it was hypothesized that proteins that adsorb onto the fiber surface play a role in the cytotoxicity and carcinogenesis of asbestos fibers. However, little is known about which proteins adsorb onto asbestos. Previously, we systematically identified asbestos-interacting proteins and classified them into eight sub-categories: chromatin/nucleotide/RNA-binding proteins, ribosomal proteins, cytoprotective proteins, cytoskeleton-associated proteins, histones and hemoglobin. Here, we report an adsorption profile of proteins for the three commercially used asbestos compounds: chrysotile, crocidolite and amosite. We quantified the amounts of adsorbed proteins by analyzing the silver-stained gels of sodium dodecyl sulfate-polyacrylamide gel electrophoresis with ImageJ software, using the bands for amosite as a standard. We found that histones were most adsorptive to crocidolite and that chromatin-binding proteins were most adsorptive to chrysotile. The results suggest that chrysotile and crocidolite directly interact with chromatin structure through different mechanisms. Furthermore, RNA-binding proteins preferably interacted with chrysotile, suggesting that chrysotile may interfere with transcription and translation. Our results provide novel evidence demonstrating that the specific molecular interactions leading to carcinogenesis are different between chrysotile and crocidolite.

In plain English

This laboratory study re-analyzed protein gels that the authors had published before. Chrysotile, crocidolite and amosite fibers had been mixed with protein extracts from MeT5A mesothelial cells or from organs (lung, kidney, liver, brain and tunica vaginalis) of male Wistar rats. The proteins that stuck to the fibers were then separated and identified. Using ImageJ software, the authors measured each protein band. They expressed the amounts on chrysotile and crocidolite as ratios to amosite because appropriate controls were lacking. Histones bound more to crocidolite than to chrysotile. Chromatin-binding proteins and RNA-binding proteins bound more to chrysotile than to crocidolite. Chrysotile's tendency to bind nucleotide-binding proteins was not statistically significant. No significant differences were found for ribosomal, cytoprotective or cytoskeleton-associated proteins, or for hemoglobin. The total amount of protein bound did not differ significantly between fiber types. The authors proposed that chrysotile and crocidolite interact with chromatin through different sets of proteins. They hypothesized that chrysotile may interfere with transcription and translation, which they said should be confirmed in future studies.

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) study: densitometry re-analysis of previously published silver-stained protein gels, with proteins identified by mass spectrometry; chrysotile compared with crocidolite by Student's t test after normalizing to amosite
• Who was studied: Protein extracts (lysates) from MeT5A human mesothelial cells and from lung, kidney, liver, brain and tunica vaginalis of male Wistar rats; no human subjects
• Exposure: Three types of asbestos fibers, chrysotile, crocidolite and amosite, obtained from the Union for International Cancer Control; amosite was used as the reference for comparison
• Main results:
  • Histones adsorbed more strongly to crocidolite than to chrysotile (statistically significant in Fig. 2A, N = 4, p less than 0.05). For example, for histone H2A type 3 the ratio to amosite was 0.49 for chrysotile and 1.34 for crocidolite.
  • Chromatin-binding proteins were more adsorptive to chrysotile than to crocidolite (Fig. 2B, N = 6, p less than 0.05). For example, for DNA replication licensing factor MCM6 the ratio to amosite was 2.11 for chrysotile and 1.22 for crocidolite.
  • RNA-binding proteins showed high adsorption to chrysotile compared with crocidolite (Fig. 3A, N = 11, p less than 0.05)
  • Chrysotile showed a tendency to adsorb nucleotide-binding proteins (Fig. 3B, N = 8), but this was not statistically significant
  • No significant differences between chrysotile and crocidolite were found for ribosomal proteins, cytoprotective proteins, cytoskeleton-associated proteins or hemoglobin
  • The total amount of protein adsorbed did not differ significantly between fiber types (data not shown)
• The authors' conclusion: The authors proposed that chrysotile and crocidolite interact with chromatin components by binding different sets of proteins. They hypothesized that chrysotile may inhibit transcription and/or translation by binding RNA-binding proteins.
• Limitations the authors state:
  • Appropriate controls were lacking, so values for chrysotile and crocidolite were normalized to amosite
  • Amounts differed protein by protein, but group results used a simple sum of ratios to amosite for simplicity
  • The idea that chrysotile interferes with transcription and translation is a hypothesis that still needs confirmation

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Crocidolite, Malignant Mesothelioma, Lung Cancer, Carcinogenesis, Amosite.

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• Putative inhibitory effects of chrysotile, crocidolite, and amosite mineral fibers on the more complex surface membrane glycolipids and glycoproteins — H.A. Newman, Y.A. Saat, et al. (1980)
• Adsorption of proteins by chrysotile and crocidolite: role of molecular weight and charge density — F. Valerio, D. Balducci, et al. (1987)
• Selective adsorption of serum proteins by chrysotile and crocidolite — F. Valerio, D. Balducci, et al. (1986)
• Infrared and nuclear magnetic resonance studies of some surface properties of asbestos-albumin interactions — R. Dumitru-Stănescu, C. Mandravel, et al. (1994)

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