beta1-integrin mediates asbestos-induced phosphorylation of AKT and ERK1/2 in a rat pleural mesothelial cell line

Our plain-English summary of beta1-integrin mediates asbestos-induced phosphorylation of AKT and ERK1/2 in a rat pleural mesothelial cell line, by A. Berken, J. Abel, K. Unfried (Oncogene, 2003).

The study

• Authors: A. Berken, J. Abel, K. Unfried
• Journal: Oncogene
• Published: 2003;22(52):8524-8
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Integrin-mediated signalling has been implicated in asbestos-induced carcinogenesis. In studies here, we examined signal transduction events associated with integrin-directed cell reactions triggered by crocidolite asbestos in the pleural mesothelial cell line 4/4 RM-4. Crocidolite fibres induced a significant time- and dose-dependent activation of the extracellular-signal-regulated kinases ERK1 and ERK2. ERK activation was specifically inhibited by integrin-blocking agents, that are integrin-binding peptides containing the sequence arginine-glycine-aspartic acid (RGD), and monoclonal antibodies against the integrin beta1-chain. Integrin-dependent activation of ERK1/2 in response to asbestos appeared to be independent of focal adhesion kinase pp125FAK (FAK) since FAK autophosphorylation remained unaffected in crocidolite-exposed mesothelial cells. Instead, we observed striking similarities in the kinetics of asbestos-induced ERK1/2 responses and phosphorylation of protein kinase B (AKT) at serine 473, a possible target residue for integrin-linked kinase. As with ERK activation, asbestos-induced AKT stimulation was significantly blocked by both the RGD-peptide and the beta1-integrin antibodies. These studies are the first to establish that in mesothelial cells ERK1/2 and AKT are simultaneously phosphorylated upon asbestos exposure in a beta1-integrin-dependent manner.

In plain English

This was a laboratory study of a cultured rat pleural mesothelial cell line, called 4/4 RM-4, not of people or animals. The authors exposed the cells to South African crocidolite asbestos and measured the activation (phosphorylation) of signalling proteins inside the cells. After 48 hours, crocidolite significantly raised activation of the proteins ERK1 and ERK2, up to threefold above sham-treated controls, and the effect increased with dose. Activation of another protein, AKT, also rose significantly, up to threefold over sham controls after 48 hours. Pretreating cells with an RGD-containing peptide, which blocks integrin receptors, or with antibodies specific to beta1-integrin significantly reduced both the ERK and AKT responses. A control peptide had virtually no effect on the ERK response and no inhibitory effect on the AKT response. A third protein, focal adhesion kinase, showed no significant change. The authors concluded that, in mesothelial cells, asbestos exposure switched on ERK1/2 and AKT at the same time in a way that depends on beta1-integrin. They noted that future studies would need to establish whether these effects are specific to crocidolite.

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 experiment on a cultured cell line, using Western blots to measure protein phosphorylation (three independent experiments in duplicate, analysed by Student's t-test)
• Who was studied: The non-tumorous rat pleural mesothelial cell line 4/4 RM-4 (cells from passages 36–44), studied in Düsseldorf, Germany
• Exposure: South African crocidolite asbestos suspended in phosphate-buffered saline. Doses were printed as 10 mg/cm2 for 0, 4, 8, 16, 24 or 48 h, and as 5, 10 or 15 mg/cm2 for 48 h; the unit may be damaged in the text. Sham controls received saline only. Some cells were pretreated with an RGD-containing peptide (RGDS), a control peptide (GRADSP), or an anti-beta1-integrin antibody (anti-CD29).
• Main results:
  • In crocidolite-exposed cells, ERK1/2 phosphorylation was significantly increased, up to threefold above sham controls, after 48 h
  • At 48 h, ERK1/2 activation was dose-dependent, with a strong increase between the 5 and 10 dose levels
  • Total ERK1/2 protein and lactate dehydrogenase release (a marker of cell damage; data not shown) did not differ significantly between asbestos-treated cells and sham controls at any time point
  • Pretreatment with the RGD-containing peptide, an integrin-blocking agent, significantly reduced asbestos-induced ERK1/2 phosphorylation
  • The GRADSP control peptide had virtually no effect on crocidolite-induced ERK activation
  • The beta1-integrin-specific antibody (anti-CD29) significantly inhibited asbestos-induced ERK1/2 activation
  • Over 48 h, neither FAK expression nor FAK phosphorylation at Y397 differed significantly between crocidolite-exposed cells and sham controls
  • In crocidolite-exposed cells, AKT phosphorylation at serine 473 was significantly increased, up to threefold over sham controls, after 48 h
  • Asbestos-induced AKT stimulation was significantly blocked by both the RGD peptide and the anti-CD29 antibodies; the GRADSP control peptide showed no inhibitory effects
• The authors' conclusion: The authors concluded that in mesothelial cells ERK1/2 and AKT are simultaneously phosphorylated upon asbestos exposure in a beta1-integrin-dependent manner
• Limitations the authors state:
  • Whether the integrin-mediated effects on ERK and AKT are specific to crocidolite asbestos is left for future studies
  • The direct involvement of integrin-linked kinase (ILK) in asbestos-induced signalling was not established
  • How fibres interact with the beta1-containing integrins was not established

Topics

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Carcinogenesis, Crocidolite, Monoclonal, Asbestos Exposure.

Related studies

• Decrease in phosphorylation of ERK following decreased expression of NK cell-activating receptors in human NK cell line exposed to asbestos — Y. Nishimura, M. Maeda, et al. (2009)
• SV40-dependent AKT activity drives mesothelial cell transformation after asbestos exposure — P. Cacciotti, D. Barbone, et al. (2005)
• The duration of nuclear extracellular signal-regulated kinase 1 and 2 signaling during cell cycle reentry distinguishes proliferation from apoptosis in response to asbestos — Z. Yuan, D.J. Taatjes, et al. (2004)
• Asbestos inhalation induces tyrosine nitration associated with extracellular signal-regulated kinase 1/2 activation in the rat lung — A. Iwagaki, N. Choe, et al. (2003)
• Activation of p38 MAP kinase by asbestos in rat mesothelial cells is mediated by oxidative stress — W.A. Swain, K.J. O'Byrne, et al. (2004)
• Human and mouse mesotheliomas exhibit elevated AKT/PKB activity, which can be targeted pharmacologically to inhibit tumor cell growth — D.A. Altomare, H. You, et al. (2005)

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