Poster Sessions

CANCER-18

Jean-Pierre Gillet

J.P. Gillet, R. Rutledge, C.P. Wu, T. Eliseeva, K. Chen, P. Fitzgerald, H. Fales, D. Xia, S. Ambudkar, M. Gottesman

The Characterization of ABCB5 Reveals a Full-length Transporter Mediating Multidrug Resistance

ABCB5 has been described as an atypical ABC transporter termed ABCB5 Beta. Recently, the same group identified ABCB5 in melanoma-initiating cells. Two ABCB5 isoforms expressed in a melanoma cancer cell line and encoding an atypical half-transporter were cloned by our laboratory. However, despite these reports, ABCB5, whose predicted full-length sequence is highly homologous to ABCB1, remains poorly characterized. We have begun a systematic study of the physiological and pathological roles of ABCB5. mRNA and EST data support the existence of at least three groups of transcripts from this locus. The largest of these represents a “full length” ABC transporter protein with two full TMD-NBD domains characteristic of many ABC transporters. Northern blotting was performed to analyze the transcript variants present in melanoma cancer cell lines and in stably transfected cell lines with constructs encoding either a full length or a beta ABCB5 form as controls. Protein sequence analysis was performed by mass spectrometry from immunoprecipitated protein, using a newly developed polyclonal antibody. Cytotoxicity studies reveal a potential role for full length ABCB5 in anthracycline, mitoxantrone and epipodophyllotoxin resistance, while its expression in clinical samples is being investigated in laser capture microdissected samples of metastatic melanoma.