Mélanome Uvéal: des prédispositions génétiques à l'oncogenèse

par Anne-céline Derrien

Projet de thèse en Hématologie-oncologie

Sous la direction de Marc-Henri Stern.

Thèses en préparation à Paris Sciences et Lettres , dans le cadre de Hématologie, oncogénèse et biothérapies , en partenariat avec Génétique et biologie des cancers (laboratoire) , Génomique et biologie des cancers du sein héréditaires (equipe de recherche) et de Institut Curie (établissement de préparation de la thèse) depuis le 02-10-2017 .


  • Résumé

    Ce projet de thèse vise à identifier les principaux facteurs génétiques à risques du mélanome uvéal (MU), et mieux comprendre la tumorigénèse du MU. Le MU est une tumeur oculaire, affectant majoritaires les populations de souche européenne. A travers une étude GWAS (Genome-Wide Association Study) comportant des patients du MU, l'équipe a identifié une région candidate comprenant des variantes génétiques à risque. Ces variantes sont localisées dans des régions non-codantes, et leur rôle oncologique reste donc inconnu. L'objectif de ce projet de thèse est de découvrir l'impact de ces variantes sur la pathogénèse du MU, à travers leur influence sur la chromatine et, par conséquent, sur la modification de la vulnérabilité des cellules à la transformation maligne. Le projet implique l'analyse de bases de données publiques, des études d'expression et de marques de chromatine, et des analyses de fonction et transformation cellulaires. Le but ultime est d'identifier les facteurs génétiques prédisposant au mélanome uvéal et à caractériser les voies biologiques et moléculaires influencées par ces facteurs.

  • Titre traduit

    From genetic predispositions to oncogenesis in uveal melanoma


  • Résumé

    The PhD project is devoted to identifying key genetic risk factors for Uveal Melanoma (UM) and refining UM tumorigenesis. UM is an ocular tumour predominantly observed in populations of European ancestry. Through a genome-wide association study (GWAS) in UM patients, the team identified a candidate susceptibility region containing risk variants. The variants are located in non-coding regions, so their oncogenic role is unknown. The aim of this PhD project is to decipher the impact of these variants on UM pathogenesis by their influence on chromatin and, as a consequence, by their modification of cell sensitivity to malignant transformation. This project implies analysis of public databases, chromatin and expression studies, and cell function and transformation analyses. The ultimate goal is to identify genetic factors predisposing to UM and to characterize the biologic and oncologic pathways influenced by these factors. Uveal melanoma (UM) is the most frequent ocular primary tumour in adults. It arises from melanocytes in the uveal tract, including the choroid, ciliary body and iris. UM represents about 4-5% of all melanomas and has an incidence rate of 5.6 cases per million person per year (~500 new cases a year in France). If the disease metastasises, generally to the liver, the prognosis is dismal as the disease is treatment refractory. Despite the common embryonic origin of their precursor neural-crest cells, there are major differences between uveal and cutaneous melanoma in terms of epidemiology, genetics, mechanisms of malignant transformation and clinical outcome. UM are genetically simple tumours with rare copy number alteration, mutually exclusive mutations of GNA11 or GNAQ genes leading to constitutive activation of these G alpha protein pathways, and mutually exclusive recurrent mutations targeting BAP1, EIF1AX and SF3B1 (associated with aberrant alternative splicing) genes. Epidemiological studies have shown that UM affects mainly populations of European ancestry, with very few cases in African-Americans and Asian populations8,9, suggesting the presence of genetic risk alleles. However, a role of pigmentation protecting against ultraviolet (UV) exposure was excluded by epidemiologic data and by the absence of UV mutational signature in this disease10. An alternative hypothesis to explain the lower incidence of UM in Afro-American and Asian populations is the prevalence of protector alleles in these populations, or conversely the prevalence of risk alleles in populations of European ancestry. Thus, the team conducted a two-stage genome wide association study (GWAS) of 259 UM patients and 401 controls in populations of European ancestry. Three candidate susceptibility loci were identified, including the locus at chromosome 5p15.33 associated with the strongest odd ratio. Furthermore, 5p polymorphisms are associated with differential expression of genes in the vicinity. This PhD project aims to identify genetic factors predisposing to UM and to characterize the biologic and oncologic pathways influenced by these factors. The goal will be to decipher the influence of the observed polymorphisms on 5p genes environment by studying chromatin marks, the binding of key transcription factors, and gene expression. The variants with the highest p- value and odd ratios will be matched with available information on the 5p region, including ENCODE marks and predicted transcription factors binding sites. We will then validate the causative role of the candidate variant on transcription factor binding and gene expression, by genome editing (CRISPR/cas9 method) in UM cell lines. We will subsequently analyse the influence of down- and up-regulation of the identified genes on malignant transformation, using cellular models of UM oncogenesis. In fine, the project will provide UM genetic susceptibility factors and their role in pathogenesis.