Nickel is a specific inhibitor for the binding of activated alpha 2-macroglobulin to the low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor.
The low density receptor-related protein/alpha 2-macroglobulin receptor (LRP/alpha 2-MR) binds to several ligands involved in lipoprotein and protease clearance. The receptor-associated protein (RAP) inhibits the binding of all known ligands. We studied the inhibition by Ni2+ of the binding of different ligands to cells and to the purified LRP/alpha 2-MR. Ni2+ inhibited all of the specific binding of radiolabeled methylamine-activated alpha 2-macroglobulin (125I-alpha 2-M*) to rabbit aortic smooth muscle cells (SMC), rat hepatoma Fu5AH, and mouse fibroblast L cells. Ni2+ also inhibited the binding of trypsin-activated alpha 2-macroglobulin to SMC but did not affect the binding of RAP, Pseudomonas exotoxin A, or low-density lipoproteins. The inhibition of alpha 2-M* binding by Ni2+ was not due to its interaction with alpha 2-M*. Preincubation of SMC with Ni2+ followed by ligand binding suggested that Ni2+ binds to cell-surface molecules and inhibits the binding of alpha 2-M* but does not affect RAP binding. Most of the binding of alpha 2-M* to SMC was due to its binding to the LRP/alpha 2-MR, as opposed to the recently described signaling receptor, as demonstrated by the inhibition of this binding by the RAP. Moreover, the inhibition of alpha 2-M* binding to the LRP/alpha 2-MR by Ni2+ was demonstrated using purified receptor immobilized on microtiter plates. Two to three molecules of 63Ni2+ bound to the immobilized receptor with equal affinity but not to alpha 2-M*. The specific binding of alpha 2-M* to the immobilized receptor was inhibited in the presence of nickel.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Pathology, Medical College of Pennsylvania, Philadelphia, USA.
M M
MM
Hussain
R K
RK
Kancha
T N
TN
Tulenko
D000818:Animals; D001013:Aorta, Thoracic / Q000166:cytology / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D007739:L Cells; D008114:Liver Neoplasms, Experimental; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology*; D011485:Protein Binding; D011817:Rabbits; D051381:Rats; D011971:Receptors, Immunologic / Q000187:drug effects / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000511:alpha-Macroglobulins / Q000187:drug effects / Q000378:metabolism*
D002121:Calcium Channel Blockers; D007457:Iodine Radioisotopes; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D000511:alpha-Macroglobulins; D009532:Nickel