Overexpression of gamma-glutamylcysteine synthetase in human malignant mesothelioma

Our plain-English summary of Overexpression of gamma-glutamylcysteine synthetase in human malignant mesothelioma, by K. Järvinen, Y. Soini, K. Kahlos, et al (Human Pathology, 2002).

The study

• Authors: K. Järvinen, Y. Soini, K. Kahlos, V.L. Kinnula
• Journal: Human Pathology
• Published: 2002;33(7):748-55
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mesothelioma is a fatal tumor resistant to all treatment modalities for reasons that are still unresolved. Glutathione (GSH)-associated pathways are induced by oxidants and cytotoxic drugs, and they are also involved in the progression and resistance of some tumor cells in vitro. The rate-limiting enzyme in GSH biosynthesis is gamma-glutamylcysteine synthetase (gamma GCS). However, the expression of this enzyme has not been systematically investigated in malignant tumors, and there are no studies of gamma GCS in biopsy specimens of malignant mesothelioma. We investigated the immunohistochemical distribution and expression of both subunits of gamma GCS in healthy pleural mesothelium, pleural mesothelioma tumor biopsy samples (34 cases), and mesothelioma cells in culture (7 cell lines). Nonmalignant mesothelium showed no immunoreactivity for either subunit in any of the cases. The heavy (catalytic) subunit of gamma GCS was highly immunostained in 29 and weakly positive in 5 cases. High-moderate and weak immunoreactivity of the light (regulatory) subunit of gamma GCS was found in 15 and 7 tumors, respectively, whereas 12 cases showed no reactivity. There was no correlation with either catalytic or regulatory subunit expression and patient survival. There was, however, a significant correlation between the heavy chain and multidrug resistance protein (MRP) 2 (P =.048), whereas no correlation was observed between the light chain and MRP1 or MRP2. Treatment of cultured mesothelioma cells with buthionine sulfoximine (BSO), to inhibit gamma GCS, significantly potentiated cisplatin-induced cytotoxicity mainly by nonapoptotic mechanism when assessed by counting the living cells, TUNEL (terminal deoxytransferase-mediated dUTP nick-end labeling) assay, and caspase-3 cleavage. In conclusion, gamma GCS is highly positive in most cases of malignant mesothelioma and may play an important role in the primary drug resistance of this tumor in vivo.

Copyright 2002, Elsevier Science (USA). All rights reserved.

In plain English

This Finnish laboratory study examined gamma-glutamylcysteine synthetase (GCS), an enzyme that limits how fast cells make glutathione, a protective substance. The authors stained pleural mesothelioma biopsy samples from 34 patients (28 men, 6 women) at Oulu University Hospital, and healthy pleura from nonsmokers. They tested seven mesothelioma cell lines with a different method (Western blot). Asbestos exposure was not studied. Healthy mesothelium showed no staining for either part (subunit) of the enzyme. The heavy subunit stained strongly in 29 of 34 tumors. The light subunit was strong or moderate in 15, weak in 7 and absent in 12. Staining showed no correlation with patient survival, tumor cell growth or apoptosis (programmed cell death). The heavy subunit did correlate significantly with a drug-transport protein, MRP2. All seven cell lines contained both subunits. In two cell lines, blocking glutathione production with a drug called BSO significantly increased the damage caused by the cancer drug cisplatin. BSO did not increase apoptosis. The authors concluded that making glutathione through GCS may be of major importance in the drug resistance of malignant cells.

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 study with two parts: immunohistochemical staining of archived tumor and healthy tissue biopsies, and Western blot analysis and drug-exposure experiments in cultured mesothelioma cell lines
• Who was studied: Mesothelioma tissue samples from 34 patients (28 men and 6 women), retrieved from the files of the Department of Pathology at Oulu University Hospital, Finland. Subtypes were epitheloid (23), sarcomatoid (7) and biphasic (4). Healthy pleura came from nonsmokers investigated for nonmalignant lung diseases. Seven mesothelioma cell lines were also studied. Study dates are not given.
• Exposure: Asbestos exposure was not assessed. In the laboratory, two cell lines (M14K and M38K) were pretreated with buthionine sulfoximine (BSO) to deplete glutathione. They were then exposed to the cancer drug cisplatin for 48 hours.
• Main results:
  • Nonmalignant (healthy) mesothelium showed no staining for either the heavy or the light subunit of GCS in any case.
  • 29 of the 34 mesothelioma tumors stained strongly for the heavy (catalytic) subunit of GCS.
  • For the light (regulatory) subunit, 15 tumors showed strong or moderate staining, 7 weak staining, and 12 no staining.
  • Neither subunit's staining correlated significantly with patient survival (P values of .07 for the heavy and .42 for the light subunit).
  • In the biopsy specimens, GCS staining showed no association with tumor cell proliferation (measured by Ki-67) or with apoptosis.
  • Heavy subunit staining correlated significantly with the drug-transport protein MRP2 (P = .048). The light subunit did not correlate significantly with MRP2 (P = .35). Neither subunit correlated with MRP1.
  • Western blot analysis of 7 mesothelioma cell lines detected both GCS subunits in all of them. The most resistant line, M38K, had the highest level of the heavy subunit.
  • In the cell experiments, BSO pretreatment to deplete glutathione significantly increased cisplatin-induced toxicity.
  • Cisplatin caused apoptosis in M14K cells but not in M38K cells, and BSO did not increase apoptosis. In M38K cells the apoptotic index stayed between 2.4% (controls) and 4.5% (cisplatin-exposed, BSO-treated cells).
• The authors' conclusion: The authors concluded that making glutathione through GCS may be of major importance in the primary drug resistance of malignant cells.
• Limitations the authors state:
  • The authors noted that finding no significant correlation with survival does not rule out an association.
  • The authors stated that tumor biopsies contain stroma and nonmalignant cells, so measuring active GCS protein or glutathione content from tumor tissue homogenates is not reliable. For this reason they assessed these in cultured cells instead.
  • The authors noted that caspase 3 cleavage is not a sensitive indicator of apoptosis, so they also assessed apoptosis by examining the cells' appearance.

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, Glutathione (GSH), Biopsy, Mesothelium, Pleural Mesothelioma, Cisplatin.

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