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Identification of mRNA coding for factor VII protein in human alveolar macrophages--coagulant expression may be
M P McGee1, R Wallin, R Devlin
1Department of Medicine, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27103.
Abstract:
Clotting factors synthesized by monocytes and macrophages may initiate coagulation reactions during inflammation. Functional vitamin K-dependent coagulation factors have been found to be associated with human monocytes/macrophages, but there are no reports identifying mRNA coding for vitamin K-dependent proteins in these cells. In the present studies, factor VII mRNA was found in total RNA extracted from freshly isolated human alveolar macrophages using hybridization with a complementary DNA probe. On the other hand, vitamin K-dependent carboxylase activity which is required for postribosomal modification of the protein, was not detectable in the macrophages before or after culture, and human blood mononuclear leukocytes also lacked this enzyme activity. Control human and rat hepatoma cells exhibited high levels of carboxylase activity within the same experiments. Using sensitive kinetic assays, no increase in factor VII activity was detected during culture of alveolar macrophages under conditions promoting 1.78 +/- .24 (n = 8) fold increases of tissue factor activity. These findings with freshly isolated cells demonstrate that alveolar macrophages synthesize factor VII mRNA in vivo. However, the mRNA was found in the absence of evidence for gamma-carboxylase activity or processing of the factor into a functional clotting enzyme. The results imply that functional expression of any synthesized coagulation factor VII in alveolar macrophages may be limited or prevented due to a cellular deficiency at the level of postribosomal processing.
Insights
Alveolar macrophages produce factor VII mRNA, a clotting factor precursor. However, they lack the necessary enzyme activity for functional factor VII production, limiting its expression during inflammation.
Area of Science:
- Immunology
- Hematology
- Molecular Biology
Background:
- Monocytes and macrophages are implicated in initiating coagulation during inflammation.
- Previous studies found vitamin K-dependent coagulation factors associated with monocytes/macrophages.
- No prior reports identified mRNA for vitamin K-dependent proteins in these cells.
Purpose of the Study:
- To investigate the synthesis of factor VII mRNA in human alveolar macrophages.
- To determine the presence of vitamin K-dependent carboxylase activity in these cells.
- To assess the functional expression of coagulation factor VII in alveolar macrophages.
Main Methods:
- Hybridization with a complementary DNA probe to detect factor VII mRNA in RNA from isolated human alveolar macrophages.
- Assays for vitamin K-dependent carboxylase activity in macrophages before and after culture.
- Kinetic assays to measure factor VII activity during macrophage culture.
Main Results:
- Factor VII mRNA was detected in freshly isolated human alveolar macrophages.
- Vitamin K-dependent carboxylase activity was not detectable in macrophages, unlike control hepatoma cells.
- No increase in factor VII activity was observed during macrophage culture, despite increased tissue factor activity.
Conclusions:
- Human alveolar macrophages synthesize factor VII mRNA in vivo.
- The absence of gamma-carboxylase activity prevents the post-translational modification of factor VII.
- Functional expression of coagulation factor VII in alveolar macrophages is likely limited by a deficiency in post-ribosomal processing.