Cloning and characterization of human adenosine 5 '-triphosphate-binding cassette, sub-family A, transporter 2 (ABCA2)

We have isolated the full-length cDNA for human ATP-binding cassette, sub-f amily A, member 2 transporter (ABCA2), The ORF of this cDNA encodes a prote in consisting of 2436 amino acids with apparent molecular weight of M-r 270 ,000. Accordingly, ABCA2 is the largest known mammalian ABC transporter des cribed thus far, Analysis of mRNA expression levels indicated that ABCA2 is highest in human brain and has a broad expression pattern in a panel of tu mor cell lines. Using specific antibodies to ABCA2 and various organelle ma rker proteins, ABCA2 was found to colocalize with the lysosomal/endosomal m arker LAMP1, forming discrete, punctate intracellular vesicles. In ABCA2-tr ansfected cells, the transporter also colocalized with a fluorescently labe led steroid analogue, estramustine. The sequestration of the steroid into t he lysosomal/ endosomal compartment indicates a potential substrate specifi city for ABCA2. Furthermore, the presence of a lipocalin signature moth in the ABCA2 sequence suggests a possible broad role for this protein in the t ransport of steroids, lipids, and related molecules.