Urokinase receptor in human malignant mesothelioma cells: role in tumor cell mitogenesis and proteolysis

Our plain-English summary of Urokinase receptor in human malignant mesothelioma cells: role in tumor cell mitogenesis and proteolysis, by S. Shetty, A. Kumar, A. Johnson, et al (The American Journal of Physiology, 1995).

The study

• Authors: S. Shetty, A. Kumar, A. Johnson, S. Pueblitz, S. Idell
• Journal: The American Journal of Physiology
• Published: 1995;268(6 Pt 1):L972-82
• Cited by: 48 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Urokinase (uPA) interacts with its receptor (uPAR) to promote proteolysis and tumor migration, functions of potential importance in the pathogenesis of malignant mesothelioma. Immunohistochemistry of human malignant mesothelioma tissue and mesothelioma cells (MS-1) showed that mesothelioma cells express uPAR. We isolated uPAR from MS-1 cells by metabolic labeling and showed that it could be induced by phorbol myristate acetate (PMA), lipopolysaccharide (LPS), a transforming growth factor-beta (TGF-beta) or tumor necrosis factor-alpha (TNF-alpha). Experiments with MS-1 cells showed that uPA binding was saturable, specific, and reversible with a mean dissociation constant (Kd) of 5.4 +/- 1.1 nM. Binding was inhibited by a blocking antibody to uPAR and by the uPA amino-terminal fragment (ATF), but not by low molecular weight uPA. uPAR expression was regulated transcriptionally and translationally; antisense oligonucleotides blocked expression of uPAR protein. Plasminogen activator inhibitor-1 (PAI-1) inhibited PA activity of preformed uPA/uPAR complexes and increased cycling of the receptor from the cell surface. Stimulation of subconfluent MS-1 cells by high molecular weight or recombinant uPA, but not ATF or low molecular weight fragment, caused concentration-dependent incorporation of [3H]thymidine. These data indicate a novel mechanism by which malignant mesothelioma cells localize pericellular proteolysis and concurrently regulate tumor cell proliferation.

In plain English

This was a laboratory (in vitro) study of human malignant mesothelioma cells. It mainly used a cultured cell line called MS-1, with a second line (REN) to confirm some results, plus stained sections of human mesothelioma tumor tissue. It did not study asbestos or any exposure in people. The authors examined the urokinase receptor (uPAR), a cell-surface protein that binds the enzyme urokinase (uPA). Tumor cells in the tissue sections stained positive for uPAR. In MS-1 cells, uPA binding had a mean dissociation constant of 5.4 plus or minus 1.1 nM. PMA increased uPAR expression fourfold, and TGF-beta, TNF-alpha or LPS increased it about threefold. A blocking antibody cut uPA binding by about 78% in PMA-stimulated cells, and an antisense molecule cut uPAR expression by 70%. Whole (high molecular weight) or recombinant uPA nearly doubled cell numbers, to 1.62 and 1.65 million cells per well against 0.9 million in controls. uPA fragments did not. The authors concluded that uPA binding to its receptor could facilitate tumor extension and may enhance tumor growth.

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 of cultured human mesothelioma cells, with immunohistochemistry of human mesothelioma tissue
• Who was studied: Cultured human malignant mesothelioma cells: the MS-1 line (a gift from Dr. M. Hsu, University of Arkansas) and a second line, REN (a gift from Dr. S. Albelda, University of Pennsylvania), used to confirm responses. Also formalin-fixed sections of human mesothelioma tumor tissue (number of specimens not stated). The work was done at the University of Texas Health Science Center at Tyler.
• Exposure: No asbestos or fiber exposure was studied. The cells were treated in the laboratory with pro-inflammatory agents (phorbol myristate acetate (PMA), bacterial lipopolysaccharide (LPS), transforming growth factor-beta (TGF-beta), tumor necrosis factor-alpha (TNF-alpha)). They were also treated with forms of urokinase (high molecular weight, low molecular weight, amino-terminal fragment and recombinant uPA), a uPAR antibody, antisense oligonucleotides and plasminogen activator inhibitor-1 (PAI-1).
• Main results:
  • In sections of human mesothelioma tissue, the tumor cells stained positive for uPAR. No staining occurred with nonspecific antibody.
  • In PMA-stimulated MS-1 cells, uPA binding had a mean dissociation constant (Kd) of 5.4 plus or minus 1.1 nM.
  • In PMA-stimulated MS-1 cells, unlabeled high molecular weight or recombinant uPA (160-fold molar excess) inhibited total uPA binding by more than 75%. Low molecular weight uPA did not inhibit binding at all.
  • In MS-1 cells, PMA stimulation enhanced uPAR expression fourfold. TGF-beta, TNF-alpha or LPS induced uPAR approximately threefold, with maximum expression 18 to 24 hours after treatment.
  • In PMA-stimulated MS-1 cells, a uPAR antibody reduced uPA binding by about 78%, compared with only 21% for nonspecific IgG. In unstimulated cells the figures were 70% versus 7%.
  • In MS-1 cells, pretreatment with an antisense-uPAR oligonucleotide inhibited uPAR expression by 70%. Nonspecific antisense and sense oligonucleotides had no effect.
  • In PMA-stimulated cells treated with preformed uPA-PAI-1 complexes, surface-bound radioactivity fell from about 80% to 24% over 3 hours, and degraded (TCA-soluble) radioactivity rose from 11% to 61%.
  • In subconfluent MS-1 cells treated with high molecular weight uPA (about 18 nM), thymidine incorporation (a measure of DNA synthesis) after 24 hours increased from 7,542 plus or minus 1642 to 14,097 plus or minus 917 cpm. Cells treated with the amino-terminal fragment took up no more thymidine than controls.
  • Wells of MS-1 cells treated with PBS contained 0.9 plus or minus 0.2 million cells after 48 hours. Wells treated with high molecular weight or recombinant uPA contained 1.62 plus or minus 0.16 and 1.65 plus or minus 0.10 million cells (P less than 0.0001). Low molecular weight uPA and the amino-terminal fragment gave counts no different from control (1.0 plus or minus 0.1 and 0.9 plus or minus 0.2 million cells).
• The authors' conclusion: The authors concluded that the binding of uPA to its receptor on MS-1 cells could facilitate tumor extension by degrading extracellular matrixes. They wrote that, because uPA-uPAR interaction was mitogenic in these cells, it may also enhance neoplastic growth. They suggested that blocking receptor binding points to potential therapeutic strategies.

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, Immunohistochemistry, Transforming Growth Factor-beta (TGF-β), Tumor Necrosis Factor-alpha (TNF-α).

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• Activated alveolar macrophages express the insulin-like growth factor-I receptor — W.N. Rom, P. Pääkkö (1991)
• Expression of growth factor and growth factor receptor RNA in rat pleural mesothelial cells in culture — E. Bermudez, J. Everitt, et al. (1990)

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