Abstract

Epigenetic modifications of histone have crucial roles in the control of gene activity, nuclear architecture, and genomic stability. In this respect, they may contribute to the development and progression of cancer. We investigated whether epigenetic changes of histone H4 are involved in lung carcinogenesis. Epigenetic modifications of histone H4 were studied by immunohistochemistry in normal lung and 157 lung carcinoma using antibodies specifically recognizing the acetylated (Ac) lysines 5 (K5), K8, K12, K16, and trimethylated (me3) K20 residues of histone H4. Western blotting was used to validate the immunohistochemistry results. H4K20me3 was also studied in 17 preneoplastic lesions. Expression of the Suv4-20h1/2 trimethyltransferases was analyzed by quantitative reverse transcription-PCR in a subset of tumor samples. As compared with normal lung, cancer cells displayed an aberrant pattern of histone H4 modifications with hyperacetylation of H4K5/H4K8, hypoacetylation of H4K12/H4K16, and loss of H4K20 trimethylation. Alteration of H4K20 trimethylation was frequent in squamous cell carcinoma (67%) and was observed in early precursors lesions in which the level of H4K20me3 staining strongly decreased with disease progression. In adenocarcinoma, the down-regulation of H4K20me3 was less frequent (28%) but allowed the identification of a subgroup of stage I adenocarcinoma patients with reduced survival (P = 0.007). Loss of H4K20 trimethylation was associated with decreased expression of Suv4-20h2, a specific H4K20 trimethyltransferase involved in telomere length maintenance. Our findings indicate an important role of histone H4 modifications in bronchial carcinogenesis and highlight H4K20me3 as a candidate biomarker for early detection of and therapeutic approaches to lung cancer.

Highlights

  • Lung cancer is the leading cause of death from cancer among males in Europe and both men and women in the USA

  • Our results demonstrate a global distorted pattern of histone H4 modifications in lung tumors and provide evidence that loss of H4K20 trimethylation plays a crucial role in lung tumorigenesis

  • One hundred non small cell lung cancers comprising 50 squamous carcinoma and 50 adenocarcinoma were analyzed by immunohistochemistry (IHC) using antibodies recognizing the acetylated (Ac) lysines 5 (K5), K8, K12 or K16 residues of histone H4

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Summary

Introduction

It is apparent that epigenetic modifications that do not affect the primary sequence of the DNA contribute to lung tumor formation These involve both global genomic hypomethylation leading to chromosomal instability, and regional hypermethylation at certain promoters [6,7,8]. They occur at the level of histones that are the targets for several post-translational covalent modifications which allow regulable contacts with the underlying DNA and affect higher-order chromatin structures [9] In this regard, histone covalent modifications influence a multitude of cellular processes [10,11,12] and aberrant histone acetylation and methylation patterns were recently reported in human tumors [13, 14]. Our results demonstrate a global distorted pattern of histone H4 modifications in lung tumors and provide evidence that loss of H4K20 trimethylation plays a crucial role in lung tumorigenesis

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