Elsevier

Human Pathology

Volume 32, Issue 8, August 2001, Pages 856-862
Human Pathology

Original Contributions
Altered global methylation of DNA: An epigenetic difference in susceptibility for lung cancer is associated with its progression*,**

https://doi.org/10.1053/hupa.2001.26471Get rights and content

Abstract

Alterations in global DNA methylation have been observed in many cancers, but whether such alterations represent an epigenetic difference in susceptibility for the disease is unknown. The status of global DNA methylation also has not been reported in intact or specific types of cells involved in the carcinogenic process. To address these issues in lung carcinogenesis, we evaluated the status of global DNA methylation by using a monoclonal antibody specific for 5-methylcytosine (5-mc) in randomly selected lung specimens of 60 cigarette smokers who developed squamous cell carcinoma (SCC) and 30 cigarette smokers who did not. 5-mc immunostaining scores of DNA of SCC (0.61 ± 0.42) and associated hyperplastic lesions (0.82 ± 0.27) was significantly lower than those of DNA of histologically normal bronchial epithelial cells (0.99 ± 0.52) and hyperplastic lesions (1.2 ± 0.22) of noncancer specimens. The ratio of 5-mc scores between SCC and matched uninvolved bronchial epithelial cells was significantly associated with advanced stage and size of the tumor. The results suggest that alteration in global DNA methylation is an important epigenetic difference in susceptibility for the development of lung cancer. The reduced global DNA methylation in SCC compared with epithelial hyperplasia and its association with tumor size and disease stage is suggestive of its involvement in the progression of SCC. The results also indicate that normal methylation of DNA in epithelial hyperplastic lesions may prevent the transformation of these lesions to invasive cancer. If these results are confirmed, the status of DNA methylation in early lesions such as epithelial hyperplasia could be used to identify smokers who are at risk for the development of SCC. HUM PATHOL 32:856-862. Copyright © 2001 by W.B. Saunders Company

Section snippets

Patients and tissue specimens

Formalin-fixed, paraffin-embedded sections of the lung were obtained from the archival collections of the Veterans Administration Hospital and University Hospital in Birmingham, AL. Thirty noncancer specimens of the lung were selected at random from a list of lung surgeries performed in smokers between 1988 and 1998 for advanced emphysema of the lung. From a list of patients with SCC of the lung who had undergone surgery between 1989 and 1996, 60 cases were selected at random. Exposure to

Results

The 5-mc scores were reproducible for individual cases as well as for a group of tissue specimens. The average coefficient of variation of the assay was 4%. The mean ±SD for 5-mc scores of the 10 tissue sections stained and evaluated on 2 different days was 1.17 ± 0.3 and 1.16 ± 0.2. The specimens of all 30 noncancer subjects had adequate normal bronchial epithelium for the evaluation of immunostaining for 5-mc. Ten noncancer specimens also had hyperplastic lesions for evaluation. Metaplastic

Discussion

The observation that only a fraction of cigarette smokers develop lung cancer during their lifetimes is intriguing. Although the genetic and epigenetic differences between smokers who develop SCC and those who do not have substantial preventive implications, this field is still in its infancy. The present study focused on global methylation of DNA, an epigenetic change in DNA that may play a central role in the multistage process of human carcinogenesis. To our knowledge, this is the first

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    *

    Supported by grant K07 CA 70160 from the National Cancer Institute.

    **

    Address correspondence and reprint requests to Chandrika J. Piyathilake, PhD, Department of Nutrition Sciences, Division of Nutritional Biochemistry and Molecular Biology, University of Alabama at Birmingham, University Station, Birmingham, AL 35294.

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