Gene expression profile of human lung epithelial cells chronically exposed to single-walled carbon nanotubes

Our plain-English summary of Gene expression profile of human lung epithelial cells chronically exposed to single-walled carbon nanotubes, by D. Chen, T.A. Stueckle, S. Luanpitpong, et al (Nanoscale Research Letters, 2015).

The study

• Authors: D. Chen, T.A. Stueckle, S. Luanpitpong, Y. Rojanasakul, Y. Lu, L. Wang
• Journal: Nanoscale Research Letters
• Published: 2015;10:12
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

A rapid increase in utility of engineered nanomaterials, including carbon nanotubes (CNTs), has raised a concern over their safety. Based on recent evidence from animal studies, pulmonary exposure of CNTs may lead to nanoparticle accumulation in the deep lung without effective clearance which could interact with local lung cells for a long period of time. Physicochemical similarities of CNTs to asbestos fibers may contribute to their asbestos-like carcinogenic potential after long-term exposure, which has not been well addressed. More studies are needed to identify and predict the carcinogenic potential and mechanisms for promoting their safe use. Our previous study reported a long-term in vitro exposure model for CNT carcinogenicity and showed that 6-month sub-chronic exposure of single-walled carbon nanotubes (SWCNT) causes malignant transformation of human lung epithelial cells. In addition, the transformed cells induced tumor formation in mice and exhibited an apoptosis resistant phenotype, a key characteristic of cancer cells. Although the potential role of p53 in the transformation process was identified, the underlying mechanisms of oncogenesis remain largely undefined. Here, we further examined the gene expression profile by using genome microarrays to profile molecular mechanisms of SWCNT oncogenesis. Based on differentially expressed genes, possible mechanisms of SWCNT-associated apoptosis resistance and oncogenesis were identified, which included activation of pAkt/p53/Bcl-2 signaling axis, increased gene expression of Ras family for cell cycle control, Dsh-mediated Notch 1, and downregulation of apoptotic genes BAX and Noxa. Activated immune responses were among the major changes of biological function. Our findings shed light on potential molecular mechanisms and signaling pathways involved in SWCNT oncogenic potential.

In plain English

This was a laboratory cell study, not a study of people. The authors used human lung bronchial epithelial BEAS-2B cells exposed in earlier work for 6 months to a sub-cytotoxic dose (0.02 micrograms per square centimetre) of dispersed single-walled carbon nanotubes (SWCNT), or to PBS, and compared genome-wide expression on Agilent microarrays, with an apoptosis protein array and Western blots. Differential expression required at least a twofold change and p of 0.05 or less. Immune-response processes were among the top altered biological processes. TP53 mRNA was moderately decreased (-1.48, p 0.66) and 13 other p53-associated transcripts showed no statistical difference; TP53INP1 (-4.86), TP53INP2 (-2.66) and TP53I3 (2.55) changed more than twofold but were not statistically significant. In Western blots the pAkt to Akt ratio was 1.7-fold higher in exposed than control cells at 0 to 5 micrograms per millilitre SWCNT, and Bcl-2 2.5-fold higher at 0 micrograms per millilitre (both p less than 0.05); both fell at higher re-exposure doses. The authors called the study a preliminary step and noted CNTs share properties with asbestos fibres.

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: In vitro laboratory study: genome-wide microarray gene expression profiling, apoptosis protein array and Western blot of a long-term SWCNT-exposed human lung epithelial cell line versus passage-matched unexposed cells
• Who was studied: Human lung bronchial epithelial BEAS-2B cells; three SWCNT-exposed biological replicates (pooled and analysed as one) and three passage-matched unexposed control samples, from the authors' earlier 6-month exposure model
• Exposure: HiPco-produced, acid-purified single-walled carbon nanotubes, 99% elemental carbon and 0.23% iron, at 0.02 micrograms per square centimetre continuously for 6 months; Western blot re-exposure used 1 to 50 micrograms per millilitre
• Main results:
  • Immune-response-related processes, including response to metal ion (enrichment score 8.6) and antigen processing and presentation of peptide antigen via MHC class I (8.5), were among the top altered biological processes in SWCNT-exposed cells
  • TP53 mRNA in exposed cells was moderately decreased (fold -1.48, p 0.66) without statistical significance; 13 other p53-associated transcripts showed no statistical difference, and three of them changed more than twofold: TP53I3 (2.55, p 0.18), TP53INP1 (-4.86, p 0.10) and TP53INP2 (-2.66, p 0.53), none meeting the study's p of 0.05 or less cutoff
  • Western blot showed a 1.7-fold increased phosphorylated Akt to Akt ratio in SWCNT-exposed (B-SWCNT) versus control cells at 0 to 5 micrograms per millilitre SWCNT
  • Bcl-2 protein was elevated 2.5-fold in B-SWCNT compared with B-Control cells at 0 micrograms per millilitre (no re-exposure)
  • After 24 h re-exposure, Bcl-2 increased in B-Control cells at 5 micrograms per millilitre or more but decreased in B-SWCNT cells at 10 micrograms per millilitre or more
  • The apoptosis protein array in B-SWCNT cells showed decreased claspin, overexpressed HSP60, a fivefold overexpressed Fas receptor, moderately decreased TNFR1, and about twofold decreased Bcl-xl and Xiap
  • Among cancer-mechanism genes, B-SWCNT cells showed increased RASGRP, ARHGEF9, SHC and RHOB and decreased RBPJK, JNK, DVL1, GSK3A, GSK3beta, PAK, AKT2, PMAIP1 (Noxa) and BAX
• The authors' conclusion: The authors concluded that the oncogenic phenotype of the SWCNT-transformed cells may be explained, among other possible mechanisms, by active pAkt signalling, destabilised p53, increased Ras family gene expression, Dsh-mediated Notch1, overexpressed Bcl-2 and downregulation of BAX and PMAIP1, and that this model plus transcriptome analysis could aid investigation of CNT carcinogenesis mechanisms
• Limitations the authors state:
  • The three treated samples were pooled and analysed as one, which the authors said lowered statistical power and introduced more false positives; they considered the study a preliminary step
  • Part of the p53 response may reflect the BEAS-2B cell model itself, since SV40 large T antigen immortalization affects p53 function
  • The authors stated the functional role of individual genes or pathways in the carcinogenic process needs further individual study

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic, Malignant Transformation, Apoptosis, Carcinogenesis.

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