Cell surface expression of the 70-kD component of Ku, a DNA-binding nuclear autoantigen.
The Ku complex, a heterodimer of 86- and 70-kD proteins, is a nuclear DNA-binding autoantigen. However, hydrophobicity analysis of the deduced amino acid sequence of the 70-kD protein had strongly suggested that this might also be a membrane protein. In the present study, using antibodies to synthetic peptides and a polyclonal antiserum to the purified protein, we show that the 70-kD protein of the Ku complex is present in isolated plasma membranes of human cells. By indirect immunofluorescence microscopy and fluorescein-activated cell sorting, we demonstrate that this autoantigen is exposed on the cell surface. In addition, we have identified several domains of the protein that are exposed. Our study provides one of the first demonstrations of a eukaryotic, nuclear DNA-binding protein that is also on the cell membrane. Moreover, our results might help explain how autoantibodies to the Ku autoantigen could target cells for an autoimmune attack.
Laboratory of Oral Medicine, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
B S
BS
Prabhakar
G P
GP
Allaway
J
J
Srinivasappa
A L
AL
Notkins
D000595:Amino Acid Sequence; D034961:Antigens, Nuclear; D000954:Antigens, Surface / Q000032:analysis* / Q000502:physiology; D001324:Autoantigens / Q000032:analysis*; D002462:Cell Membrane / Q000276:immunology; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000032:analysis* / Q000502:physiology; D006367:HeLa Cells / Q000276:immunology; D006801:Humans; D000072200:Ku Autoantigen; D008969:Molecular Sequence Data
D034961:Antigens, Nuclear; D000954:Antigens, Surface; D001324:Autoantigens; D004268:DNA-Binding Proteins; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen