Characterization of ABCB5 transporters in multidrug resistance mechanisms and their physiological functions

Résumé

Abstract Background: ABCB5 is a member of the ATP-binding cassette (ABC) transporter superfamily. They mediate the ATP-driven transport a wide variety of substrates against their chemical gradient. Mostly, they have been studied for their implication in multidrug resistance (MDR). In human, they efflux out of the cancer cell or sequester in organelles different chemotherapeutics resulting in treatment failure. ABCB5 encodes several transcripts, the two longest ones encoding transporters, ABCB5FL and ABCB5β, respectively. Because of its conformation, ABCB5β needs to homo- or heterodimerize to become functional. Aim: A recent study in our laboratory revealed two ABCB5 heterodimers with basal ATPase activity: ABCB5β/ABCB6 and ABCB5β/ABCB9. In the literature, there is some evidence that ABCB5 is involved in MDR, however, few studies have specified which isoform was investigated, rendering the interpretation of the data difficult. Therefore, we wanted to investigate the role of ABCB5 transporters and its interacting partners, ABCB6 and ABCB9, in MDR. Moreover, we decided to characterize the pharmacological profile of both transporter and further investigate their physiological function which, as proposed in the literature, could be linked with melanin production or transport. Results: Due to transfection issues, we could only express GFP_ABCB5FL, GFP_ABCB5β and GFP_ABCB9 transporters in HEK293T and MelJuso, but no change in viability was observed when treated with increased concentration of doxorubicin. To avoid transient transfection, we then used a UACC257 cell line knockout for the ABCB5 gene in MTT assays to compare the effect of loss of expression of all ABCB5 isoforms on cell viability following treatment with doxorubicin, docetaxel, and paclitaxel. Surprisingly, UACC257 ABCB5 KO cells were more resistant to all three treatments than wild-type cells. Furthermore, we showed that the pharmacological profiles of ABCB5FL and ABCB5β are identical. Finally, we showed that ABCB5FL could be involved in melanin transport while no significative results were obtained regarding both isoforms implication in melanogenesis. Conclusion: ABCB5FL and ABCB5β implication in MDR could not be determined, nevertheless, potential compensatory mechanisms were highlighted. On the other hand, both transporters showed similar pharmacological profiles. Finally, further investigations are needed regarding their implication in melanin transport and melanogenesis.

la date de réponse	16 janv. 2024
langue originale	Anglais
L'institution diplômante	Universite de Namur
Superviseur	Jean-Pierre Gillet (Promoteur)