Identification of a gene signature of a pre-transformation process by senescence evasion in normal human epidermal keratinocytes.

Nathalie Martin,Guillemette Marot,Corinne Abbadie,Louise Ott,Predrag Slijepcevic,Olivier Pluquet,Clara Salazar-Cardozo,Chantal Vercamer

doi:10.1186/1476-4598-13-151

Abstract

BackgroundEpidemiological data show that the incidence of carcinomas in humans is highly dependent on age. However, the initial steps of the age-related molecular oncogenic processes by which the switch towards the neoplastic state occurs remain poorly understood, mostly due to the absence of powerful models. In a previous study, we showed that normal human epidermal keratinocytes (NHEKs) spontaneously and systematically escape from senescence to give rise to pre-neoplastic emerging cells.MethodsHere, this model was used to analyze the gene expression profile associated with the early steps of age-related cell transformation. We compared the gene expression profiles of growing or senescent NHEKs to post-senescent emerging cells. Data analyses were performed by using the linear modeling features of the limma package, resulting in a two-sided t test or F-test based on moderated statistics. The p-values were adjusted for multiple testing by controlling the false discovery rate according to Benjamini Hochberg method.The common gene set resulting of differential gene expression profiles from these two comparisons revealed a post-senescence neoplastic emergence (PSNE) gene signature of 286 genes.ResultsAbout half of these genes were already reported as involved in cancer or premalignant skin diseases. However, bioinformatics analyses did not highlight inside this signature canonical cancer pathways but metabolic pathways, including in first line the metabolism of xenobiotics by cytochrome P450. In order to validate the relevance of this signature as a signature of pretransformation by senescence evasion, we invalidated two components of the metabolism of xenobiotics by cytochrome P450, AKR1C2 and AKR1C3. When performed at the beginning of the senescence plateau, this invalidation did not alter the senescent state itself but significantly decreased the frequency of PSNE. Conversely, overexpression of AKR1C2 but not AKR1C3 increased the frequency of PSNE.ConclusionsTo our knowledge, this study is the first to identify reprogrammation of metabolic pathways in normal keratinocytes as a potential determinant of the switch from senescence to pre-transformation.

Highlights

Epidemiological data show that the incidence of carcinomas in humans is highly dependent on age
Identification of a post-senescence neoplastic emergence (PSNE) gene expression signature To establish a gene signature specific of the earliest steps of tumorigenesis, we performed a transcriptomic analysis of post-senescent emergent Normal human epidermal keratinocyte (NHEK) in comparison with senescent and young ones
The oxidoreductase genes AKR1C2 and AKR1C3 promote PSNE We investigated by genetics and pharmacological approaches whether the Aldo-keto reductase 1C (AKR1C) genes activated at senescence in primary keratinocytes may function as oncogenes, i.e. promote senescence evasion in the form of pre-transformed cells

Summary

Introduction

Epidemiological data show that the incidence of carcinomas in humans is highly dependent on age. To override the normal mechanisms controlling cellular proliferation, transformed cells accumulate somatic or inherited mutations in several tumor suppressor genes, oncogenes and genes that are involved in maintaining genomic stability [1,2]. Another driving condition of transformation is the chromosomal instability which includes loss of heterozygosity (LOH), aneuploidy, chromosome translocation and gene amplifications [3]. When transcriptional profiling utilizes cell lines, it often involved isogenically matched non-transformed and transformed cells through overexpression of telomerase (hTERT) and oncogenes such as v-Src [7], H-Ras [8] These approaches make not possible to kinetically follow initial and intermediate stages between normal and fully transformed cells. The current clinical models lack initial phases and the current in vitro culture models lack the importance of the order of the events

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