Study of the subcellular localization of the human ATP-binding cassette transporter isoform, ABCB5β, expressed in melanoma.

Promoter

Prof. Jean-Pierre GILLET, Department of biomedical sciences, Molecular Physiology Research Unit (URPhyM), Laboratory of Molecular Cancer Biology (LBMC) 

Jury

• Prof. Henri-François Renard, Biology Department, University of Namur (president)
• Prof. Olivier de Backer, Biomedical sciences department, University of Namur
• Prof. Abele Rupert, Institute of Biochemistry, Biocenter, Goethe-Universität Frankfurt
• Prof. Gergely Szakacs, Research Unit for Chemical Safety and Cancer Prevention, Medical University of Vienna
• Prof. Jean-Pierre Gillet (supervisor)
• Prof. Marielle Boonen (co-supervisor)

Summary

ABCB5β is a member of the ABC transporter superfamily cloned from melanocytes. It has been reported as a marker of skin progenitor cells and melanoma stem cells. ABCB5β has also been shown to exert an oncogenic activity and to promote cancer metastasis. However, this protein remains poorly characterized. To elucidate its subcellular localization, we tested several anti-ABCB5 antibodies and prepared several tagged ABCB5β cDNA constructs. We then used a combination of immunofluorescence and biochemical analyses to investigate the presence of ABCB5β in different subcellular compartments of HeLa and MelJuSo cell lines. Treatment of the cells with the proteasome inhibitor MG132 showed that part of the population of newly synthesized ABCB5β is degraded by the proteasome system. Interestingly, treatment with SAHA, a molecule that promotes chaperone-assisted folding, largely increased the expression of ABCB5β. Nevertheless, the overall protein distribution in the cells remained similar to control conditions; the protein extensively colocalized with the endoplasmic reticulum marker calnexin. Taken together with cell surface biotinylation studies demonstrating that the protein does not reach the plasma membrane (even after SAHA treatment), the data indicate that ABCB5β is a microsomal protein predominantly localized to the ER.

This work is supported by the University of Namur (Namur, Belgium) through the UNamur-CERUNA institutional PhD grant