Fra-1 governs cell migration via modulation of CD44 expression in human mesotheliomas

Our plain-English summary of Fra-1 governs cell migration via modulation of CD44 expression in human mesotheliomas, by M.E. Ramos-Nino, S.R. Blumen, H. Pass, et al (Molecular Cancer, 2007).

The study

• Authors: M.E. Ramos-Nino, S.R. Blumen, H. Pass, B.T. Mossman
• Journal: Molecular Cancer
• Published: 2007;6:81
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Silencing of Fra-1, a component of the dimeric transcription factor, activator protein-1 (AP-1), inhibits mRNA expression of c-met and cd44 in rat mesothelioma cells and is causally linked to maintenance of the transformed phenotype. However, the mechanisms of Fra-1 regulation and Fra-1 regulated gene expression in human malignant mesothelioma (MM) are unclear. We first show in a panel of human MM cells that Fra-1 mRNA expression in MM is complex and regulated by extracellular signal-regulated kinase (ERK1, ERK2), Src, and phosphatidyl-inositol-3-kinase (PI3K) pathways in a tumor-specific fashion. Cell lines with PI3K-dependent Fra-1 expression were SV40 positive and expressed the lowest basal Fra-1 levels. Levels of Fra-1 expression correlated with amounts of CD44 expression that were greater in simian virus 40 negative (SV40-) MM cells. Using dominant negative (dn), short hairpin (sh) and small interference (si) RNA constructs, we next demonstrate that expression of CD44, the principal hyaluronic receptor in MMs, correlates with Fra-expression in both simian virus 40 positive (SV40+) and SV40- MMs. Moreover, both Fra-1 and CD44 expression are linked to cell migration in SV40- MM cells. Lastly, in contrast to normal lung tissue, tissue microarrays revealed that Fra-1 was expressed in 33 of 34 human MMs, and that all CD44+ tumors were SV40-. These results suggest that Fra-1 is associated with cell migration in human MMs and that Fra-1 modulation of CD44 may govern migration of selected MMs.

In plain English

This laboratory study examined the transcription factor Fra-1 and the hyaluronic acid receptor CD44 in human malignant mesothelioma (MM). The authors used a panel of seven human pleural MM cell lines (MM1, MM2, MM5, MM6 negative for SV40 large T-antigen; MM3, MM4, MM7 positive) together with tissue microarrays of resected human MM. The PI3K inhibitor LY294002 (20 micromolar) significantly reduced Fra-1 mRNA in 3 of the 4 lines first examined, while the EGFR inhibitor AG1478 had no effect; the Src (PP2) and MEK (PD98059) inhibitors each reduced Fra-1 in 2 of the 4 lines. Fra-1 and CD44 protein were markedly lower in the SV40-positive lines. Knockdown constructs against Fra-1 lowered CD44 expression. In the SV40-negative line MM1, shFra-1 or shCD44 significantly reduced cell migration compared with empty-vector controls (p less than 0.05). In a separate test, Fra-1 knockdown (shFra-1) reduced hyaluronic acid uptake in SV40-negative cells. In the tissue arrays, 33 of 34 MMs stained positively for Fra-1. Of the 34, 17 (50%) were SV40+ and 8 (24%) were CD44+, and all SV40+ tumours were CD44-. The authors concluded that Fra-1 governs MM cell migration partly through indirect modulation of CD44.

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 of human mesothelioma cell lines using signalling-pathway inhibitors, dominant negative and RNA interference constructs, and migration and hyaluronic acid uptake assays, plus immunofluorescence of human tumour tissue microarrays
• Who was studied: Seven human pleural mesothelioma cell lines (MM1 to MM7; MM1, MM2, MM5 and MM6 SV40-negative; MM3, MM4 and MM7 SV40-positive) and tissue microarrays of 34 resected human mesotheliomas, with normal lung tissue as control
• Exposure: Not an asbestos exposure study. Cells were treated with kinase inhibitors (LY294002 at 10 and 20 micromolar for PI3K, PP2 at 10 micromolar for Src, PD98059 at 30 micromolar for MEK1/2, AG1478 at 10 micromolar for EGFR), stimulated with serum, and given dominant negative or shRNA constructs against Fra-1 and CD44
• Main results:
  • In the cell lines first examined, PI3K inhibition reduced Fra-1 mRNA in 3 of 4 lines, while EGFR inhibition had no effect
  • Src or MEK1 inhibition each reduced Fra-1 expression in 2 of the 4 lines
  • In the three SV40-positive cell lines, Fra-1 and CD44 protein were markedly lower than in the SV40-negative lines
  • A shFra-1 construct reduced CD44 expression in both an SV40-positive and an SV40-negative MM line
  • Promoter analysis did not indicate direct participation of Fra-1 in CD44 expression (data not shown)
  • In the SV40-negative line MM1, the number of migrating cells was significantly decreased with shFra-1 or shCD44 compared with empty-vector controls. No migration was detected in the SV40-positive MM3 lines
  • Uptake of fluorescent hyaluronic acid was decreased in SV40-negative MM cells transfected with shFra-1. Hyaluronic acid was not internalised in the SV40-positive line
  • In the tissue microarrays, 33 of 34 mesotheliomas stained positively for Fra-1. Intensity scores were about 3% score 0, 29% score 1, 27% score 2 and 41% score 3
  • In the SV40/CD44 array of 34 mesotheliomas, 17 (50%) were SV40+ and 8 (24%) were CD44+, and all SV40+ tumours were CD44-
  • Increased phosphorylated ERK1/2 immunoreactivity, mainly cytoplasmic, was seen in about 30% of the tumours
• The authors' conclusion: The authors concluded that Fra-1 is activated through multiple survival pathways and that its expression governs human mesothelioma cell migration, partly through indirect modulation of CD44 expression

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, SV40.

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