DNA methylation and associated gene expression in blood prior to lung cancer diagnosis in the Norwegian Women and Cancer cohort

Torkjel Manning Sandanger,Florence Guida,Dorret I Boomsma,Paolo Vineis,Charlotta Rylander,Mattias Johansson,Eiliv Lund,Marc Chadeau-Hyam,Roel Vermeulen,David C Muller,Therese Haugdahl Nøst,Jenny Van Dongen,Gianluca Campanella

doi:10.1038/s41598-018-34334-6

Abstract

The majority of lung cancer is caused by tobacco smoking, and lung cancer-relevant epigenetic markers have been identified in relation to smoking exposure. Still, smoking-related markers appear to mediate little of the effect of smoking on lung cancer. Thus in order to identify disease-relevant markers and enhance our understanding of pathways, a wide search is warranted. Through an epigenome-wide search within a case-control study (131 cases, 129 controls) nested in a Norwegian prospective cohort of women, we found 25 CpG sites associated with lung cancer. Twenty-three were classified as associated with smoking (LC-AwS), and two were classified as unassociated with smoking (LC-non-AwS), as they remained associated with lung cancer after stringent adjustment for smoking exposure using the comprehensive smoking index (CSI): cg10151248 (PC, CSI-adjusted odds ratio (OR) = 0.34 [0.23–0.52] per standard deviation change in methylation) and cg13482620 (B3GNTL1, CSI-adjusted OR = 0.33 [0.22–0.50]). Analysis among never smokers and a cohort of smoking-discordant twins confirmed the classification of the two LC-non-AwS CpG sites. Gene expression profiles demonstrated that the LC-AwS CpG sites had different enriched pathways than LC-non-AwS sites. In conclusion, using blood-derived DNA methylation and gene expression profiles from a prospective lung cancer case-control study in women, we identified 25 CpG lung cancer markers prior to diagnosis, two of which were LC-non-AwS markers and related to distinct pathways.

Highlights

Lung cancer is the leading cause of cancer death worldwide, causing as many deaths as the four most deadly cancers combined, and the incidence of lung cancer is projected to double by 20501
It is of interest to identify lung cancer biomarkers that are unrelated to smoking exposure to (i) gain better understanding of the etiology of lung cancer and (ii) to investigate whether biological pathways affected by smoking-induced changes in DNA-methylation are similar to those affected by differential methylation at CpG sites that are not associated with smoking exposure
Estimated cell type proportions were similar in cases and controls, except for the natural killer cells, which were underrepresented in cases and among current smokers (Table S2)

Summary

Introduction

Lung cancer is the leading cause of cancer death worldwide, causing as many deaths as the four most deadly cancers combined (breast, prostate, colon, and pancreas), and the incidence of lung cancer is projected to double by 20501. Smoking is an established causal risk factor responsible for a vast proportion of lung cancer incidence, identified smoking-related CpG sites have been shown to mediate some or little of the effects of smoking on lung cancer[6,15]. It is of interest to identify lung cancer biomarkers that are unrelated to smoking exposure to (i) gain better understanding of the etiology of lung cancer and (ii) to investigate whether biological pathways affected by smoking-induced changes in DNA-methylation are similar to those affected by differential methylation at CpG sites that are not associated with smoking exposure. We used full-resolution DNA methylation profiles from prospectively collected blood samples to identify methylation alterations in relation to future lung cancer diagnosis and assess the relationship between these markers and smoking exposure. We exploited gene expression data measured in the same individuals to aid functional interpretation by exploring biological pathways of gene expression profiles affected by methylation changes at all lung cancer-related CpG sites

Methods

Results

Conclusion