Ligation of low-density lipoprotein receptor-related protein with antibodies elevates intracellular calcium and inositol 1,4, 5-trisphosphate in macrophages.
We have probed the signaling characteristics of the macrophage low-density lipoprotein receptor-related protein (LRP) with monoclonal antibody 8G1, its Fab and F(ab')(2) fragments directed against the ligand binding heavy chain, and monoclonal antibody 5A6 directed against the membrane-spanning light chain of LRP. Ligation of LRP with 8G1, its Fab and F(ab')(2) fragments, or 5A6 increased intracellular Ca(2+) levels two- to threefold. Prior ligation of LRP with 8G1 did not affect the increase in [Ca(2+)](i) observed on subsequent ligation of LRP with lactoferrin, P. exotoxin A, or lipoprotein lipase. Binding to LRP by 8G1, its Fab and F(ab')(2) fragments, or 5A6 increased inositol 1,4,5-trisphosphate (IP(3)) levels by 50 to 100%. Incubation of macrophages with guanosine 5', 3'-O(thio)-triphosphate (GTP-gamma-S) before treatment with antibody potentiated and sustained the 8G1-induced increase in IP(3) levels. Treatment of macrophages with guanyl-5'-yl thiophosphate prior to GTP-gamma-S treatment abolished the GTP-gamma-S-potentiated increase in IP(3) levels in 8G1-treated macrophages. Antibody-induced increases in IP(3) and [Ca(2+)](i) in macrophages on ligation of LRP were pertussis toxin sensitive. Binding of 8G1 or its Fab or F(ab')(2) fragments to LRP stimulated macrophage protein kinase C (PKC) activity as evaluated by histone IIIs phosphorylation by about two- to sevenfold. Staurosporin inhibited the anti-LRP antibody-induced increase in PKC activity. Ligation of LRP with 8G1 increased cellular cAMP levels about twofold. Preincubation of macrophage with the LRP-binding protein receptor-associated protein suppressed the 8G1-induced increase in cAMP levels. Thus, binding of antibodies directed against either chain of LRP triggers complex signaling cascades.
Misra
U K
UK
Department of Pathology, Duke University Medical Center, Durham, North Carolina, 27710, USA.
Gawdi
G
G
Pizzo
S V
SV
D036002:ADP Ribose Transferases; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology*; D001427:Bacterial Toxins; D001666:Binding Sites, Antibody / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005098:Exotoxins / Q000378:metabolism / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D007140:Immunoglobulin Fab Fragments / Q000276:immunology / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007781:Lactoferrin / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D008071:Lipoprotein Lipase / Q000378:metabolism / Q000494:pharmacology; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D037342:Pertussis Toxin; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011973:Receptors, LDL / Q000737:chemistry / Q000276:immunology / Q000502:physiology*; D015290:Second Messenger Systems / Q000187:drug effects*; D037521:Virulence Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D000911:Antibodies, Monoclonal; D001427:Bacterial Toxins; D002118:Calcium; D000242:Cyclic AMP; D005098:Exotoxins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020962:Heterotrimeric GTP-Binding Proteins; D007140:Immunoglobulin Fab Fragments; D015544:Inositol 1,4,5-Trisphosphate; D007781:Lactoferrin; D008024:Ligands; D008071:Lipoprotein Lipase; D037342:Pertussis Toxin; D011493:Protein Kinase C; D011973:Receptors, LDL; D037521:Virulence Factors; D010566:Virulence Factors, Bordetella; D000097668:Pseudomonas aeruginosa Exotoxin A