Cell association and degradation of pregnancy zone protein-chymotrypsin complex in cultured human monocytes.
125I-labelled pregnancy zone protein complexed with chymotrypsin (PZP-ct) bound to freshly isolated and to cultured human monocytes. Binding of uncomplexed 125I-pregnancy zone protein (PZP) was less than 20% of complex binding. At 4 degrees C, labelled PZP-ct complex bound to cultured monocytes with a half-time of about 4 h. Dissociation at 4 degrees C was slow at low receptor occupancies (t 1/2 greater than 24 h). At high receptor occupancies, dissociation was biphasic (initial k-1 = 8 X 10(-3) min-1) and 85% of the cell-associated label had dissociated within 24 h. At near equilibrium, binding of 20 pmol/l 125I-PZP-ct was half maximally inhibited at a ligand concentration of about 450 pmol/l. The Scatchard plot was linear giving an estimated concentration of 2 X 10(4) receptors/cell. Ligand bound at 4 degrees C was rapidly internalized at 37 degrees C (half-time = 0.5 min) and after a 5-10 min lag time, radioactivity comprising monoiodotyrosine was released into the medium following a sigmoidal curve. At 37 degrees C the uptake of 125I-PZP-ct complex was initially linear and within 15 min internalized label accumulated, reaching a steady state at about 85% of the cell-associated radioactivity. Following a lag time of 15 min, radioactivity soluble in trichloroacetic acid appeared in the medium. Similar results were obtained with 125I-alpha 2-macroglobulin-trypsin complex (alpha 2M-T). It is concluded that high affinity receptors mediate binding, uptake and degradation of pregnancy zone protein--and alpha 2-macroglobulin-proteinase complex in human monocyte-macrophages.
D002478:Cells, Cultured; D002850:Chromatography, Gel; D002918:Chymotrypsin / Q000378:metabolism*; D004705:Endocytosis; D006801:Humans; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D009000:Monocytes / Q000378:metabolism*; D011257:Pregnancy Proteins / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000378:metabolism*
D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011257:Pregnancy Proteins; D011971:Receptors, Immunologic; C028939:alpha-2-macroglobulin-trypsin complex; D000511:alpha-Macroglobulins; D002918:Chymotrypsin; D014357:Trypsin