Expression of the Wilms' tumor gene WT1 in human malignant mesothelioma cell lines and relationship to platelet-derived growth factor A and insulin-like growth factor 2 expression

Our plain-English summary of Expression of the Wilms' tumor gene WT1 in human malignant mesothelioma cell lines and relationship to platelet-derived growth factor A and insulin-like growth factor 2 expression, by A.W. Langerak, K.A. Williamson, K. Miyagawa, et al (Genes, Chromosomes & Cancer, 1995).

The study

• Authors: A.W. Langerak, K.A. Williamson, K. Miyagawa, A. Hagemeijer, M.A. Versnel, N.D. Hastie
• Journal: Genes, Chromosomes & Cancer
• Published: 1995;12(2):87-96
• Cited by: 46 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mutations in the WT1 tumor suppressor gene are known to contribute to the development of Wilms' tumor (WT) and associated gonadal abnormalities. WT1 is expressed principally in the fetal kidney, developing gonads, and spleen and also in the mesothelium, which lines the coelomic cavities. These tissues develop from mesenchymal components that have subsequently become epithelialized, and it has therefore been proposed that WT1 may play a role in this transition of cell types. To test the possible involvement of this gene in malignant mesothelioma, we have first studied its expression in a panel of human normal and malignant mesothelial cell lines. WT1 mRNA expression levels varied greatly between the cell lines and no specific chromosomal aberration on 11p, which could be related to the variation in WT1 expression in these cell lines, was observed. Furthermore, no gross deletions rearrangements, or functionally inactivating point mutations in the WT1 coding region were identified. All four WT1 splice variants were observed at similar levels in these cell lines. The WT1 gene encodes a zinc-finger transcription factor and the four protein isoforms are each believed to act as transcriptional repressors of certain growth factor genes. Lack of WTI expression in thus predicted to result in growth stimulation of tumor cells. Binding of one particular WT1 isoform construct to the insulin-like growth factor 2 (IGF2) and platelet-derived growth factor A (PDGFA) gene promoters has been demonstrated to result in repression of these genes in transient transfection studies. Analysis of IGF2 and PDGFA mRNA expression levels compared with WTI mRNA expression levels failed to demonstrate an inverse correlation in the mesothelial cell lines, which endogenously express these genes. Finally, the putative role of WT1 in the transition of cell types was investigated. No obvious correlation between WT1 expression levels and cell morphology of the malignant mesothelial cell lines was evident from this study. Moreover, no change in WT1 expression was observed in normal mesothelial cells which were, by alteration of culture conditions, manipulated to switch from the mesenchymal to epithelial morphology.

In plain English

This laboratory study used cultured cell lines, plus an initial test of pleural fluid cells from four patients, and did not study asbestos exposure. The authors measured WT1, a gene linked to the childhood kidney cancer Wilms' tumor, in pleural mesothelioma and normal mesothelial cell lines. WT1 was consistently expressed in the normal lines. In mesothelioma lines it ranged from very high (Mero-25) to nearly or totally undetectable in several. This did not match any specific chromosome change on 11p or 11p copy number, and the WT1 gene showed no gross rearrangement or selective amplification. Expressing lines scanned for small mutations showed none of the kind that disable the protein; the only change, in three lines, did not alter the protein. In expressing lines, all four forms of the gene's message occurred in similar proportions. WT1 levels showed no clear relationship to the growth factor genes PDGFA and IGF2 or to cell shape. The authors concluded that WT1 may act as a tumor suppressor in a minority of mesotheliomas. They noted that mutations might lie in unexamined parts of the gene.

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 gene expression and gene structure in human cell lines, using Northern and Southern blots, RT-PCR, cytogenetics and point mutation screening, with an initial look at pleural effusion cells from patients
• Who was studied: Human pleural malignant mesothelioma cell lines (Mero series; the methods list Mero-14, -25, -41, -48b, -48c, -72, -82, -83, -84, -95, -96 and -123) and five normal mesothelial cell lines (NM-1, -4, -5, -9 and -12). The authors also tested pleural effusion cells from four malignant mesothelioma patients (data not shown).
• Exposure: No asbestos exposure was studied. The study measured expression of the WT1 gene in cell lines.
• Main results:
  • WT1 mRNA was consistently expressed in the normal mesothelial cell lines and was not expressed in a minority of malignant mesothelioma cell lines.
  • Among the mesothelioma cell lines, WT1 expression ranged from very high in Mero-25 to nearly or totally undetectable in Mero-41, -72, -82, -83 and -95.
  • No specific chromosomal aberration on chromosome arm 11p could be correlated with WT1 expression level in the mesothelioma cell lines.
  • The number of copies of chromosome arm 11p (aneuploidy) did not correlate with WT1 mRNA level in the cell lines.
  • Southern blots showed no gross rearrangements of the WT1 gene in the malignant cell lines. The WT1 gene was not differentially amplified in any of the cell lines, although the number of copies of 11p may vary.
  • In the WT1-expressing mesothelioma cell lines scanned, no functionally inactivating nonsense or missense mutations were found. The only base change was a C to T transition at nucleotide 768 in exon 1, present in Mero-48b, -48c and -123, which does not change the amino acid.
  • In the WT1-expressing mesothelial cell lines, all four WT1 splice variants were found, with little variation in their ratios.
  • PDGFA expression was generally higher in the mesothelioma cell lines than in the normal mesothelial cell lines, but there was no clear correlation between WT1 and PDGFA expression.
  • No clear relationship, reciprocal or otherwise, was seen between WT1 and IGF2 mRNA levels (6.0 kb transcript; the authors state the same holds true for the 4.8 kb transcript).
  • WT1 expression did not clearly correlate with the epithelial or fibrous shape of the mesothelioma cell lines, although the highest level was in Mero-25, the most clearly epithelial line.
  • When two normal mesothelial cell lines were made to take a more epithelial shape by removing EGF and hydrocortisone from the culture medium, their WT1 level did not change significantly (data not shown).
  • WT1 mRNA expression was observed in cells from pleural effusions of four malignant mesothelioma patients (data not shown).
• The authors' conclusion: The authors concluded that their results suggest WT1 may play a role as a tumor suppressor gene in a minority of human mesotheliomas. They found no evidence in these cell lines for a WT1 role in the shift from mesenchymal to epithelial cell type.
• Limitations the authors state:
  • The first 256 bp of exon 1 were left out of the point mutation scan because that region could not be amplified by PCR.
  • Undetected mutations may exist in the 5'-most coding region of exon 1 or in untranslated or intronic sequences, and cell lines without WT1 expression may carry mutations in promoter or control regions.
  • A more quantitative assay is needed to compare the proportions of the splice variants with earlier findings in other tissues.
  • The lack of a link between WT1 and cell shape was found in cultured cells and may be different in the body.
  • The study measured natural (endogenous) expression in cell lines, unlike the earlier transfection studies. Other factors in these cells may mask any regulation of PDGFA and IGF2 by WT1.
  • WT1 expression seen in pleural fluid from four mesothelioma patients cannot simply be attributed to tumor cells, because the fluids also contain other cell types.

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Platelet-Derived Growth Factor (PDGF), Tumor Suppressor Gene, Mesothelium, Mesothelial Cells.

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