Activated human T lymphocytes express albumin binding proteins which cross-react with alpha-fetoprotein.
The kinetics of iodinated human serum albumin ([125I]Hu-SA) and alpha-fetoprotein ([125I]Hu-AFP) binding and endocytosis by resting and phytohemagglutinin (PHA)-activated human T lymphocytes were studied comparatively. The binding of both SA and AFP appeared considerably increased upon blastic transformation. SA, like AFP, binds in a saturable way to the surface of PHA-stimulated human T lymphocytes at 4 degrees C and is endocytosed at 37 degrees C. Two saturation plateaus were observed by incubating at 4 degrees C activated T lymphocytes with [125I]Hu-AFP at different concentrations (10 ng-250 micrograms/ml), while only one saturation plateau was obtained by incubating cells with [125I]Hu-SA in the same conditions. Scatchard analysis of binding data revealed two types of binding sites for Hu-AFP and one for Hu-SA. Competition experiments using proteins of human and bovine origin are in favor of the presence on the surface of these cells of a common binding site for AFP and SA. Pulse-chase experiments showed that internalized [125I]SA was released mainly in a degraded form from the cells, in agreement with detection by ultrastructural cytochemistry of peroxidase-conjugated SA in lysosome-like bodies by ultrastructural cytochemistry. This contrasts with the intracellular pathway of AFP, which as previously described (Geuskens, M., et al., Eur. J. Cell Biol. 50, 418-427 (1989)), moves to tubular-vesicular structures in the Golgi region and is recycled for the most part undegraded.
Torres
J M
JM
Institut de Recherches Scientifiques sur le Cancer (CNRS), Villejuif, France.
Geuskens
M
M
Uriel
J
J
D000418:Albumins / Q000378:metabolism*; D001667:Binding, Competitive / Q000502:physiology; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000097:blood*; D003429:Cross Reactions / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008213:Lymphocyte Activation / Q000502:physiology; D012709:Serum Albumin / Q000032:analysis / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism*; D000509:alpha-Fetoproteins / Q000378:metabolism*
D000418:Albumins; D002352:Carrier Proteins; D012709:Serum Albumin; D000509:alpha-Fetoproteins