Défense de thèse de doctorat en Sciences biomédicales et pharmaceutiques

Involvement of the ABCB5 transporter in the development and progression of cutaneous melanoma

Jury

Prof. Isabelle Maystadt, Président du jury ; Prof. Nicolas Gillet ; Prof. Olivier Vanakker; Prof. Giovanna Chimini ; Prof. Michel Jadot, Co-promoteur ; Prof. Jean-Pierre Gillet, Promoteur

Résumé

The purpose of our research was to understand the role of ABCB5 in the development and progression of melanoma, the most aggressive skin cancer, which is responsible for 65% of deaths from skin cancer. Although primary melanoma is associated with a relatively good prognosis, this latter is poor after metastases development. Metastatic melanoma is associated with a median survival time of 6 months and a 5-year survival rate of 5 to 7%. Treatment resistance remains an obstacle and mainly explains the poor clinical outcome.
The comprehensive analysis of the ABCB5 coding region in 640 melanoma samples identified recurrent mutations in 13.75% of the samples analysed. Mutations were located on a 3-D predicted model based on the mouse Pgp structure. Four mutations, associated with a low SIFT score and representative of the mutational pattern, were further investigated. The ATPase assays showed that these mutations resulted in a decrease in ABCB5 basal ATP hydrolysis.
The first axis of this thesis is the in vitro study of the involvement of the ABCB5 transporter in melanomagenesis. Overexpression of the ABCB5 mutants and the silencing of ABCB5 in melanoma cell lines led to an increase of their proliferation and migration abilities, compared with the cells overexpressing wild type ABCB5. These observations suggest that ABCB5 is a tumor suppressor gene.
The second axis of this thesis is the investigation of the role of ABCB5 in melanoma development in vivo. Further analyses showed that the melanoma samples mutated in ABCB5, were also carrying alterations in the NRAS and CDKN2a genes (in 75 and 62,5 % of the samples analyzed, respectively). So, we performed a pilot study to assess the silencing of ABCB5 in mouse models harbouring these genetic alterations.
Lastly, we wanted to determine the molecular mechanism underlying the role of ABCB5 in melanomagenesis. To do this, we further studied its subcellular localization in melanoma cells. Using cell fractionation, preliminary data revealed an enrichment of ABCB5 in the nuclear and the microsomal fractions.

 

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