The THP-1 cell line is a urokinase-secreting mononuclear phagocyte with a novel defect in the production of plasminogen activator inhibitor-2.
Mononuclear phagocytes regulate the generation of plasmin by secreting urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-2 (PAI-2). We investigated the production of plasminogen activator (PA) and PA inhibitor by the human monocytic leukemia cell line, THP-1. Similar to U937 monoblast-like cells and peripheral blood monocytes (PBM), THP-1 cells produce a PA that is specifically neutralized by anti-uPA antibody and comigrates with human high molecular mass uPA (54 kDa) on casein-plasminogen zymogaphy. PA activity could be dissociated from intact THP-1 cells by brief treatment with a weak acid-glycine buffer, indicating that the uPA is secreted and bound to receptors on the plasma membrane. Regulation of uPA proceeds normally in THP-1 cells, with cell-associated PA activity increasing from 77 +/- 20 to 163 +/- 26 and 325 +/- 30 mPU/10(6) cells in response to PMA and LPS, respectively; parallel increases in steady state levels of uPA mRNA were observed. In contrast to normal expression of uPA activity, functional PAI-2 could not be demonstrated in either the conditioned media or cell lysates of THP-1 under basal or stimulated conditions. Both U937 and PBM secrete low levels of PA inhibitor activity that increase substantially in response to stimulation with PMA and LPS. Immunoreactive PAI-2, measured by ELISA, was undetectable in THP-1 lysates or conditioned medium, but was consistently present in U937 and PBM, paralleling the presence of PA inhibitor activity. THP-1 cells express low levels of an abnormally sized mRNA for PAI-2 and demonstrate a regulatory defect whereby steady state levels of PAI-2 mRNA are markedly reduced upon stimulation with PMA or LPS. By contrast, U937 and PBM respond to identical stimulation with increases in PAI-2 mRNA. We conclude that THP-1 cells express a structurally abnormal species of PAI-2 mRNA, with complete loss of inhibitory activity as well as altered function of PMA- and LPS-responsive regulatory elements.
Gross
T J
TJ
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0360.
Sitrin
R G
RG
D015152:Blotting, Northern; D003429:Cross Reactions; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007951:Leukemia, Myeloid / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D009000:Monocytes / Q000502:physiology*; D015849:Plasminogen Inactivators / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014568:Urokinase-Type Plasminogen Activator / Q000096:biosynthesis* / Q000235:genetics
D008070:Lipopolysaccharides; D015849:Plasminogen Inactivators; D012333:RNA, Messenger; D014568:Urokinase-Type Plasminogen Activator; D013755:Tetradecanoylphorbol Acetate