Human ABCB6 localizes to both the outer mitochondrial membrane and the plasma membrane.
Expression of the ATP-binding cassette transporter ABCB6 has been associated with multiple cellular functions, including resistance to several cytotoxic agents, iron homeostasis, and porphyrin transport. To further elucidate its physiological function and/or role in drug resistance, we determined the subcellular location of ABCB6. Using three novel ABCB6-specific antibodies, Western blot analysis of cells expressing cDNA-derived or endogenous ABCB6 revealed two distinct molecular weight forms. Confocal microscopy indicates that the protein localizes to both mitochondria and the plasma membrane. Differential centrifugation revealed that the lower molecular weight form predominantly resides in the mitochondria, while the larger protein form is more abundant in the plasma membrane. Preliminary studies indicate that ABCB6 is functionally relevant in the plasma membrane, where its expression prevents the accumulation of specific porphyrins in the cell. Digitonin solubilization of mitochondria demonstrated that ABCB6 is present in the outer mitochondrial membrane, while back-titration assays with the ABCB6-specific antibodies reveal that the nucleotide binding domain of ABCB6 is cytoplasmic. These studies are the first to demonstrate that ABCB6 exists in two molecular weight forms, is localized to both the outer mitochondrial membrane and the plasma membrane, and plays a functional role in the plasma membrane.
Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, DHHS, Bethesda, Maryland 20892-4256, USA.
Jill K
JK
Paterson
Suneet
S
Shukla
Chelsea M
CM
Black
Tokushi
T
Tachiwada
Susan
S
Garfield
Stephen
S
Wincovitch
David N
DN
Ernst
Anissa
A
Agadir
Xuelin
X
Li
Suresh V
SV
Ambudkar
Gergely
G
Szakacs
Shin-Ichi
S
Akiyama
Michael M
MM
Gottesman
D018528:ATP-Binding Cassette Transporters / Q000032:analysis / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D051336:Mitochondrial Membranes / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding
C107991:ABCB6 protein, human; D018528:ATP-Binding Cassette Transporters