Binding and processing of (125)I-ACTH by isolated rat splenic lymphocytes.
The effect of incubation temperature and ligand competition was tested for (125)I-ACTH binding to isolated rat lymphocytes. AlphaMSH but not Agouti-like peptide was an effective competitive inhibitor for cell surface binding at 4 degrees C. Cells incubated with (125)I-ACTH at 37 degrees C rapidly associated ligand for 10 min and then gradually lost the radioactivity with time. Cells incubated with (125)I-ACTH at 4 degrees C accumulated ligand to only about half the maximal amount when compared to cells incubated at 37 degrees C for 10 min. Temperatures below 20 degrees C and toxins that block lysosomal degradation blocked the loss of cell-associated radioactivity. These results suggest the lymphocyte ACTH receptor is the Melanocortin 5 receptor and the receptor is internalized by endocytosis to deliver ligand to the lysosome.
Clarke
B L
BL
School of Medicine, University of Minnesota at Duluth, 10 University Drive, Duluth, Minnesota 55812, USA. bclarke@d.umn.edu
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D054366:Agouti Signaling Protein; D000818:Animals; D001667:Binding, Competitive; D004705:Endocytosis; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D007976:Leupeptins / Q000494:pharmacology; D008214:Lymphocytes / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D008985:Monensin / Q000494:pharmacology; D011485:Protein Binding; D011506:Proteins / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018043:Receptors, Corticotropin / Q000378:metabolism; D044101:Receptors, Melanocortin; D013154:Spleen / Q000378:metabolism*; D013696:Temperature; D000521:alpha-MSH / Q000494:pharmacology
D054366:Agouti Signaling Protein; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D007976:Leupeptins; D011506:Proteins; D018043:Receptors, Corticotropin; D044101:Receptors, Melanocortin; C086971:melanocortin 5 receptor; D000521:alpha-MSH; D000324:Adrenocorticotropic Hormone; D008985:Monensin; C032854:leupeptin