ABCB5

ABCB5 is a member of the ATP Binding Cassette (ABC) transporter superfamily, encoded by the ABCB5 gene located on chromosome 7p11.2 in humans. The protein functions as a transmembrane ATPase that transports a variety of substrates across cellular membranes, although its specific physiological substrates remain incompletely defined. Like other ABCB transporters, ABCB5 contains two transmembrane domains and two nucleotide-binding domains that hydrolyze ATP to drive transport. Sequence analysis demonstrates that ABCB5 shares conserved motifs with other ABCB members, including Walker A and B motifs, the signature LSGGQ motif, and a transmembrane domain architecture typical of full-size ABC transporters.

ABCB5 is normally expressed at low levels in many adult tissues but is highly enriched in a subset of hair follicle stem cells, epidermal melanocytes, and retinal pigment epithelial cells. Functional studies suggest that ABCB5 contributes to drug resistance in melanoma cells by effluxing chemotherapeutic agents, and its expression has been linked to stem cell–like properties and tumor initiation. In mice, the orthologous gene is expressed in the skin, placenta, and brain, and knockout models show mild developmental abnormalities but no overt phenotype, indicating redundancy with other transporters. Human variants of ABCB5 have been investigated in association studies of melanoma risk and inflammatory conditions, though clear causal links remain to be established.

Emerging evidence from single‑cell RNA‑seq technologies indicates that ABCB5 delineates a distinct hair follicle stem cell subpopulation with heightened proliferative potential. In vivo assays demonstrate that ABCB5+ cells contribute to wound healing and hair regeneration. Additional research is ongoing to clarify the molecular mechanisms by which ABCB5 regulates cellular transport, stem cell maintenance, and susceptibility to chemoresistance.