A novel sterol-regulated surface protein on chicken fibroblasts.
In the laying hen, two different receptors for apolipoprotein B (apoB)-containing lipoproteins are expressed on somatic cells and oocytes, respectively. The somatic protein has an apparent Mr of 130,000, while the oocyte receptor is a 95-kDa protein (1989. K. Hayashi, J. Nimpf, and W. J. Schneider, J. Biol. Chem. 264:3131-3139). In order to investigate the yet unresolved relationship between these two proteins, we applied immunoblotting with anti-receptor antibodies to extracts of oocytes and chicken embryo fibroblasts. IgG fractions that recognize the 95-kDa oocyte receptor did not cross-react with the somatic receptor; however, chicken fibroblasts as well as ovarian granulosa cells that had been exposed to sterols (cholesterol and 25-OH-cholesterol) or low density lipoprotein (LDL) were shown to express a novel immunoreactive protein with an apparent Mr of 110,000. This protein is localized on the cell surface, and is unable to bind apoB-containing lipoproteins. The formation of the 110-kDa protein in fibroblasts is induced in time- and concentration-dependent fashion by sterols, concomitant with a progressive decrease in the amount of functional 130-kDa receptor protein. Following its induction, exposure of cells to LDL, but not to high density lipoprotein, caused the disappearance of the immunoreactive protein. Furthermore, the production of the 110-kDa protein did not require protein synthesis. These data are compatible with the notion that this novel receptor-related, nonfunctional protein is a truncated intermediate in the degradation pathway for the 130-kDa apoB receptor, and that the truncation generates antigenic epitope(s) shared by the 95-kDa oocyte receptor and the 110-kDa protein, but not expressed on the somatic receptor.
Hayashi
K
K
Department of Biochemistry, University of Alberta, Edmonton, Canada.
Ando
S
S
Stifani
S
S
Schneider
W J
WJ
D000818:Animals; D001055:Apolipoproteins B / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002645:Chickens; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008970:Molecular Weight; D009865:Oocytes / Q000378:metabolism; D013261:Sterols / Q000378:metabolism*
D001055:Apolipoproteins B; D008565:Membrane Proteins; D013261:Sterols