Ultrastructural studies of the intracellular translocation of endocytosed alpha-foetoprotein (AFP) by cytochemistry and of the uptake of 3H-arachidonic acid bound to AFP by autoradiography in rat rhabdomyosarcoma cells.
A covalent conjugate of alpha-foetoprotein (AFP) and horseradish peroxidase (HRP) has been used to follow, at the ultrastructural level, the pathway of AFP uptake and translocation in a rat rhabdomyosarcoma cell line. The cells were incubated for several times at 4 degrees C and/or 37 degrees C, and fixed. AFP-HRP was found to enter the cells via coated pits and receptosomes and to move to tubular elements of the trans-reticular portion of the Golgi. Some observations suggest that AFP can be recycled back to the cell surface. On the other hand, the cells were incubated with a noncovalent conjugate of AFP and 3H-arachidonic acid [3H-(20:4)], and the uptake of the fatty acid molecules studied by ultrastructural autoradiography. The cytoplasmic labeling, very low after an incubation in the presence of [3H-(20:4)]-AFP for 2 hours at 4 degrees C, increased rapidly after transfer of the cells for 5 minutes to 37 degrees C. These observations support the hypothesis that AFP plays a role in the intracellular delivery of polyunsaturated fatty acids.
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D004705:Endocytosis; D006735:Horseradish Peroxidase; D051381:Rats; D011956:Receptors, Cell Surface / Q000032:analysis; D018000:Receptors, Peptide; D012208:Rhabdomyosarcoma / Q000378:metabolism / Q000648:ultrastructure*; D000509:alpha-Fetoproteins / Q000378:metabolism*
D001095:Arachidonic Acids; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; D000509:alpha-Fetoproteins; C489009:alpha-fetoprotein receptor, rat; D016718:Arachidonic Acid; D006735:Horseradish Peroxidase