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Generation of macrophage migration inhibitory activity by plasminogen activators
Abstract:
Medium from cultures of simian virus 40-transformed mouse 3T3 cells (SV3T3) inhibits the migration in vitro of peritoneal exudate cells (macrophages) from guinea pigs while medium from untransformed 3T3 cultures does not [Hammond, M. E., Robbin, R. D., Dvorak, A. M., Selvaggio, S. S., Black, P. H. & Dvorak, H. F. (1974) Science 185, 955-957]. The present paper describes the generation of migration inhibitory factor (MIF)-like activity for peritoneal exudate cells from guinea pigs after incubation of a serum-free harvest fluid from SV3T3 cells with guinea pig serum. Inhibited macrophages lose a densely staining material from the cell surface coat compared with uninhibited guinea pig peritoneal exudate cells. The factor in SV3T3 harvest fluids which generates the migration inhibitory activity appears to be plasminogen activator, i.e., a serine protease, because (i) plasminogen activator activity and the factor which generates MIF-like activity copurify, and co-chromatograph on Sephadex G-200 columns, and (ii) plasminogen activator activity and capacity to generate MIF-like activity are simultaneously lost upon treatment with [3H]diisopropylfluorophosphate. In addition, a purified preparation of a known plasminogen activator, human urokinase, can also generate MIF-like activity upon reaction with guinea pig serum. Because transformation of 3T3 cells by SV40 increases their plasminogen activator secretion, enhanced secretion of plasminogen activator by SV3T3 cells may explain why formation of MIF-like activity is observed in SV3T3 but not 3T3 cultures. These results reveal a biochemical pathway whereby a product secreted by virus-transformed cells affects one function of a cell central to the host's immunological defense system.
Insights
Simian virus 40-transformed cells secrete a factor that generates migration inhibitory factor (MIF)-like activity in guinea pig serum, impacting macrophage function. This activity is linked to plasminogen activator, a key enzyme involved in immune responses.
Area of Science:
- Immunology
- Cell Biology
- Virology
Background:
- Simian virus 40-transformed mouse 3T3 cells (SV3T3) secrete factors that inhibit guinea pig macrophage migration.
- Untransformed 3T3 cells do not exhibit this inhibitory effect on macrophage migration.
Purpose of the Study:
- To investigate the mechanism behind the migration inhibitory activity observed in SV3T3 cell cultures.
- To identify the specific factor secreted by SV3T3 cells responsible for generating migration inhibitory factor (MIF)-like activity.
Main Methods:
- Incubation of serum-free SV3T3 cell harvest fluid with guinea pig serum to generate MIF-like activity.
- Biochemical analysis, including copurification, co-chromatography on Sephadex G-200, and treatment with [3H]diisopropylfluorophosphate, to identify the active factor.
- Testing the ability of purified human urokinase, a known plasminogen activator, to generate MIF-like activity.
Main Results:
- SV3T3 cell harvest fluid, when incubated with guinea pig serum, generated MIF-like activity.
- The factor responsible for this activity was identified as plasminogen activator, a serine protease.
- Inhibited macrophages showed a loss of cell surface coat material.
- Purified human urokinase also generated MIF-like activity upon reaction with guinea pig serum.
- Enhanced plasminogen activator secretion by SV3T3 cells correlates with MIF-like activity generation.
Conclusions:
- Virus-transformed cells secrete plasminogen activator, which can generate MIF-like activity in the presence of serum.
- This pathway demonstrates how products from virus-transformed cells can modulate immune cell function.
- The findings reveal a biochemical link between viral transformation, secreted enzymes, and immune cell migration inhibition.