DNA methylation status of REIC/Dkk-3 gene in human malignancies

Our plain-English summary of DNA methylation status of REIC/Dkk-3 gene in human malignancies, by T. Hayashi, H. Asano, S. Toyooka, et al (Journal of Cancer Research and Clinical Oncology, 2012).

The study

• Authors: T. Hayashi, H. Asano, S. Toyooka, K. Tsukuda, J. Soh, T. Shien, N. Taira, Y. Maki, N. Tanaka, H. Doihara, Y. Nasu, N.H. Huh, S. Miyoshi
• Journal: Journal of Cancer Research and Clinical Oncology
• Published: 2012;138(5):799-809
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: The REIC (reduced expression in immortalized cells)/Dkk-3 is down-regulated in various cancers and considered to be a tumor suppressor gene. REIC/Dkk-3 mRNA has two isoforms (type-a,b). REIC type-a mRNA has shown to be a major transcript in various cancer cells, and its promoter activity was much stronger than that of type-b. In this study, we examined the methylation status of REIC/Dkk-3 type-a in a broad range of human malignancies.

Methods: We examined REIC/Dkk-3 type-a methylation in breast cancers, non-small-cell lung cancers, gastric cancers, colorectal cancers, and malignant pleural mesotheliomas using a quantitative combined bisulfite restriction analysis assay and bisulfate sequencing. REIC/Dkk-3 type-a and type-b expression was examined using reverse transcriptional PCR. The relationships between the methylation and clinicopathological factors were analyzed.

Results: The rate of REIC/Dkk-3 type-a methylation ranged from 26.2 to 50.0% in the various primary tumors that were examined. REIC/Dkk-3 type-a methylation in breast cancer cells was significantly heavier than that in the other cell lines that we tested. REIC/Dkk-3 type-a methylation was inversely correlated with REIC/Dkk-3 type-a expression. There was a correlation between REIC/Dkk-3 type-a and type-b mRNA expression. REIC/Dkk-3 type-a expression was restored in MDA-MB-231 cells using 5-aza-2'-deoxycytidine treatment. We found that estrogen receptor-positive breast cancers were significantly more common among the methylated group than among the non-methylated group.

Conclusions: REIC/Dkk-3 type-a methylation was frequently detected in a broad range of cancers and appeared to play a key role in silencing REIC/Dkk-3 type-a expression in these malignancies.

In plain English

This was a laboratory study from Okayama University, Japan, of a gene called REIC/Dkk-3, which is thought to help suppress tumors. The authors measured DNA methylation, a chemical tagging that can switch a gene off, in the gene's type-a promoter region. They tested surgically removed tumors and cancer cell lines. The tumors were 37 breast, 42 lung, 21 gastric and 20 colon cancers, plus 45 malignant pleural mesotheliomas: 18 from Japanese hospitals and 27 from a US cancer center. The article did not study asbestos or any other exposure. Methylation was found in 7 of 27 (25.9%) US mesotheliomas, 7 of 18 (38.9%) Japanese mesotheliomas and 0 of 4 mesothelioma cell lines. In the other primary tumor types it ranged from 26.2% to 50.0%, with no significant differences among tumor types. It was not detected in 10 normal breast and 10 normal lung tissues. In cell lines, more methylation went with lower gene activity, and a demethylating drug restored activity in one breast cancer cell line. The authors concluded that methylation was responsible for silencing the type-a form. They noted their case numbers may have been too small for survival analysis.

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 of DNA methylation and gene expression in surgically resected tumor specimens and cancer cell lines
• Who was studied: Surgically resected tumors: 37 primary breast cancers, 42 primary non-small-cell lung cancers (NSCLCs), 21 primary gastric cancers and 20 primary colon cancers from Okayama University Hospital, Japan. Malignant pleural mesotheliomas (MPMs) came from four sources: 7 from Okayama University Hospital, 6 from Okayama Rousai Hospital, 5 from National Sanyo Hospital (18 Japanese in total) and 27 from Karmanos Cancer Center (MI, USA). The study also used 10 non-malignant breast and 10 non-malignant lung tissues, plus cell lines (7 breast cancer, 11 lung cancer, 4 MPM and 6 prostate cancer). Dates of collection were not given.
• Exposure: No asbestos or other environmental or occupational exposure was studied. The study measured methylation of the REIC/Dkk-3 type-a gene promoter and expression of the gene's type-a and type-b mRNA.
• Main results:
  • Methylation (defined as more than 10% digested bands) was found in 7 of 27 (25.9%) USA primary MPMs and 7 of 18 (38.9%) Japanese primary MPMs.
  • Methylation was found in 0 of 4 MPM cell lines.
  • Methylation was found in 16 of 37 (43.2%) primary breast cancers and in 7 of 7 (100%) breast cancer cell lines.
  • Methylation was found in 11 of 42 (26.2%) primary lung cancers.
  • Methylation was found in 10 of 20 (50.0%) primary colon cancers. In primary gastric cancers it was 8 of 21 (38.1%).
  • Methylation was not detected in 10 normal breast tissues or 10 normal lung tissues.
  • Methylation was more frequent in breast cancer cell lines than in lung (p = 0.02), MPM (p = 0.01) and prostate (p = 0.04) cancer cell lines. No significant differences were seen among the primary breast, lung, MPM, gastric and colon cancers.
  • In the cell lines, type-a methylation was inversely correlated with type-a expression (p less than 0.01).
  • In the cell lines, type-a and type-b expression were correlated (p less than 0.01).
  • Treatment with the demethylating drug 5-Aza-CdR restored type-a expression in the heavily methylated breast cancer cell line MDA-MB-231.
  • In primary breast cancers, estrogen receptor (ER)-positive cases were more common in the methylated group than in the non-methylated group (p = 0.03). By Table 3, 11 of 19 (58%) ER-positive cancers were methylated, compared with 4 of 18 (22%) ER-negative cancers.
  • No significant relationships were found between methylation and the other clinicopathological factors examined.
• The authors' conclusion: The authors concluded that DNA methylation of REIC/Dkk-3 type-a was responsible for silencing type-a expression. They also concluded that the type-a promoter was frequently methylated in breast, lung, gastric, colon and prostate cancers and in MPMs.
• Limitations the authors state:
  • The number of cases may have been too small for survival analysis, because the study's primary purpose was to detect methylation and relate it to expression.
  • Results could not be compared directly with a previous breast cancer study, because that study examined type-b rather than type-a methylation.

Topics

Medical terms in this study, explained in our Lexicon: Tumor Suppressor Gene, Lung Cancer, Stomach Cancer, Colorectal Cancer, Pleural Mesothelioma.

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