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Colon
Evaluation of global DNA hypomethylation in human colon cancer tissues by immunohistochemistry and image analysis
  1. F J Hernandez-Blazqueza,
  2. M Habibb,
  3. J-M Dumollardc,
  4. C Barthelemyd,
  5. M Benchaibe,
  6. A de Capoaf,
  7. A Niveleaug
  1. aFaculdade de Zootecnia e Engenharia de Alimentos, Universidad de São Paulo, Pirassununga (SP), Brazil, bCentre Commun de Quantimétrie Faculté de Médecine, Université Claude Bernard Lyon I, 8 Avenue Rockefeller, 69373 Lyon, France, cService d'Anatomie et Cytologie Pathologiques, Hopital Bellevue, CHRU, 42055 Saint-Etienne, France, dService d'Hépatologie et Gastroenterologie, Hopital Nord, CHRU, 42055 Saint-Etienne France, eLaboratoire de Biologie de la Reproduction, Faculté de Médecine, Université Claude Bernard Lyon I, 8 Avenue Rockefeller, 69373 Lyon, France, fDipartimento di Citogenetica e Biologia Molecolare, Università di Roma La Sapienza, via Lancisi 29, 00161 Roma, Italia, gUPRESA 5082 CNRS Université Joseph Fourier de Grenoble, Domaine de La Merci, 38706 La Tronche, France
  1. A Niveleau. Alain.Niveleau{at}ujf-grenoble.fr

Abstract

BACKGROUND Global hypomethylation of DNA is frequently observed in human tumours. This alteration is detected in early adenomas in colorectal tumorigenesis. Information is currently acquired after extraction of DNA from tissues, digestion with nucleases, and analysis by reverse phase chromatography, or treatment with restriction enzymes followed by gel electrophoresis analysis and Southern hybridisation with radiolabelled probes.

AIMS The purpose of our work was to evaluate the global methylation status of DNA in malignant lesions without loosing the histopathological features of the samples.

PATIENTS The investigation was performed on paired normal-tumour tissues from 13 patients undergoing surgical resection of colorectal adenocarcinomas.

METHODS Antibodies raised against 5-methylcytidine can be used to label methyl rich regions in interphase nuclei. This technique was adapted to the study of paraffin embedded tissues and an immunohistochemical method was developed to assess the global methylation status of individual nuclei while preserving cell morphology and tissue architecture. Computer assisted quantification of the staining intensity was performed on malignant and normal zones of human colon tissues to test the correlation between the immunolabelling signal and the respective histological patterns observed.

RESULTS Qualitative and quantitative differences were observed and measured between the normal and malignant part of each sample. Morphologically altered nuclei displayed densely labelled spots within faintly labelled areas whereas normal nuclei were darker and uniformly stained. Image analysis allowed calculation of the average integrated optical density of the nuclei in both types of tissues, demonstrating a constant and significantly lower intensity for the former type of cells.

  • colon adenocarcinoma
  • DNA hypomethylation
  • immunohistochemistry

  • Abbreviations used in this paper

    PBS
    phosphate buffered saline
    PBST
    PBS containing 0.1% Tween 20
    HPLC
    high pressure liquid chromatography
    5-MeCyt
    5-methylcytosine
    5-MeCyd
    5-methylcytidine
    PBS-BSA
    PBS-bovine serum albumin

    • https://doi.org/10.1136/gut.47.5.689

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    • Abbreviations used in this paper

      PBS
      phosphate buffered saline
      PBST
      PBS containing 0.1% Tween 20
      HPLC
      high pressure liquid chromatography
      5-MeCyt
      5-methylcytosine
      5-MeCyd
      5-methylcytidine
      PBS-BSA
      PBS-bovine serum albumin
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