Downregulation of M-CSF receptors by lipopolysaccharide in murine peritoneal exudate macrophages is mediated through a phospholipase C dependent pathway.
Murine peritoneal exudate macrophages (PEM) co-express granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage CSF (M-CSF) receptors, among others. Treatment of PEM with lipopolysaccharide (LPS) or tumor-promoting phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) induces a rapid but transient loss of M-CSF receptors in PEM. GM-CSF receptors are not affected by this treatment. The loss of M-CSF receptors induced by LPS can be inhibited by neomycin and compound 48/80, two potent phospholipase C (PLC) inhibitors, but not by phospholipase A2, calpain, protein kinase C (PKC) or protease inhibitors. On the other hand, the loss of M-CSF receptors induced by TPA has been prevented by PKC inhibitors but not by PLC inhibitors. PLC inhibitors also prevent LPS-suppressed receptor-mediated internalization of radiolabeled recombinant human (rh) M-CSF by macrophages. Similar prevention of LPS-induced M-CSF receptor downregulation was observed in human monocytes that had been pretreated with PLC inhibitors. Our results show that 1) TPA-induced M-CSF receptor loss is strictly dependent on PKC activation; 2) PLC activation alone also leads to downregulation of M-CSF receptors; and 3) LPS-induced M-CSF receptor downregulation in PEM is mediated primarily through a PLC-dependent pathway. Our data also imply that the expression of M-CSF but not GM-CSF receptors is linked to an important, yet unknown, PLC-sensitive component(s) whose hydrolysis may lead to downregulation of M-CSF receptors.
Department of Internal Medicine, Wayne State University School of Medicine, Detroit, MI 48202.
B D
BD
Chen
T H
TH
Chou
L
L
Sensenbrenner
D000818:Animals; D001202:Ascitic Fluid / Q000166:cytology; D015536:Down-Regulation; D005260:Female; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D008070:Lipopolysaccharides; D011994:Recombinant Proteins; D016173:Macrophage Colony-Stimulating Factor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D016186:Receptor, Macrophage Colony-Stimulating Factor; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate