Possible role of Marcks in the cellular modulation of monocytic tissue factor-initiated hypercoagulation.
The enhanced extrinsic tissue factor (TF)-initiated coagulation, often resulting from sepsis, could lead to disseminated intravascular coagulation presenting cardiovascular complications. Using model human leukaemia THP-1 monocytes, we studied monocytic TF (mTF) hypercoagulation and its regulation. After an 8 h exposure to bacterial endotoxin [lipopolysaccharide (LPS); 100 ng/ml], mTF activity was significantly upregulated as the result of the enhanced mTF synthesis. Thereafter, LPS induction declined, exhibiting a "quiescent-desensitizing' phenomenon. Such diminished LPS induction was,however,associated with sustained LPS-enhanced mTF synthesis, revealing the possible occurrence of a post-translational downregulation. It was noted that LPS desensitization was accompanied by the increased expression of myristoylated alanine-rich C kinase substrate (Marcks). In contrast, A23187 (20 micromol/l) or Quin-2AM (20 micromol/l) drastically activated mTF activity without detectable effect on mTF synthesis; both of which showed that sustained functional upregulation during 24 h culture did not enhance Marcks expression. These inverse correlations between mTF activity upregulation and Marcks expression suggested that Marcks could be inhibitory. Marcks phosphorylation site domain (151-175) (Marcks PSD) readily inhibited mTF-dependent FVII activation and diminished FVIIa formation in LPS-challenged cells. As a result, Marcks PSD offset LPS-induced mTF hypercoagulation upon inclusion in the single-stage clotting assays. The anticoagulant activity was confirmed by showing that Marcks PSD significantly blocked rabbit brain thromboplastin (rbTF) procoagulation and inhibited rbTF-dependent FVII activation as well as FVIIa formation. Our study suggests that Marcks expression plays a role in a novel cellular modulation to downregulate mTF hypercoagulation.
Department of Surgery, School of Medicine, Wayne State University, 416 Lande Medical Research Building, 550 E. Canfield, Detroit, MI 48201, USA. ad5742@wayne.edu
Arthur J
AJ
Chu
Shi-Hua
SH
Lin
Evano
E
Piasentin
D015153:Blotting, Western; D002135:Calcium-Binding Proteins; D005167:Factor VII / Q000502:physiology; D005959:Glucosidases; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007938:Leukemia / Q000097:blood*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008565:Membrane Proteins; D009000:Monocytes / Q000502:physiology*; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010750:Phosphoproteins / Q000502:physiology*; D019851:Thrombophilia / Q000209:etiology*; D015854:Up-Regulation
D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; C000619710:MARCKS protein, human; D008565:Membrane Proteins; D010750:Phosphoproteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D005167:Factor VII; D005959:Glucosidases; C070368:PRKCSH protein, human