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Synthesis and secretion of a mitogenic protein by macrophages: description of a superinduction phenomenon
Abstract:
We have examined the biosynthesis and fate of the mitogenic protein (MP)2 made by macrophages. This mitogenic protein was assayed by its stimulation of DNA synthesis of thymocytes. Macrophages freshly harvested from the peritoneal cavity did not contain MP in the cell. The MP, however, rapidly appeared in the cell, reaching maximum amount by 1 to 2 hr, maintaining its concentration up to about 6 hr, and then disappearing. The disappearance of MP did not correlate with its secretion into the medium. The elaboration of MP stimulated by contact with the dish was inhibited by cycloheximide. Exposure of the cells to inhibitors of protein synthesis after 1 to 2 hr of culture at a time when the MP was already made produced a striking increase in secretion. The MP inside the cell did not appear to decay in the presence of cycloheximide. This result thus represents another example of superinduction. The intracellular fate of MP appears to be under the regulation of a control protein.
Insights
Macrophages produce a mitogenic protein (MP) that stimulates DNA synthesis. MP levels peak within hours and then decline, with its intracellular fate regulated by a control protein, showcasing a superinduction phenomenon.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages are key immune cells involved in various biological processes.
- Mitogenic protein (MP) produced by macrophages plays a role in stimulating DNA synthesis.
- Understanding the regulation of MP biosynthesis and degradation is crucial for immune response studies.
Purpose of the Study:
- To investigate the biosynthesis and intracellular fate of macrophage-derived mitogenic protein (MP).
- To elucidate the mechanisms regulating MP production and degradation.
- To identify factors influencing MP secretion and stability.
Main Methods:
- Assaying MP activity by measuring its stimulation of thymocyte DNA synthesis.
- Culturing macrophages and monitoring MP levels over time using biochemical assays.
- Utilizing cycloheximide and other protein synthesis inhibitors to study MP elaboration and degradation.
- Investigating MP secretion into the culture medium.
Main Results:
- Newly harvested macrophages initially lack MP, which rapidly appears intracellularly, peaking at 1-2 hours and sustained for up to 6 hours.
- MP disappearance from the cell did not correlate with its secretion into the medium.
- Contact-stimulated MP elaboration was inhibited by cycloheximide.
- Inhibiting protein synthesis after MP synthesis initiation led to increased secretion, indicating superinduction.
- Intracellular MP did not degrade in the presence of cycloheximide, suggesting regulation by a control protein.
Conclusions:
- Macrophage-derived mitogenic protein (MP) exhibits a regulated synthesis and degradation cycle.
- MP intracellular fate is controlled by a regulatory protein, leading to superinduction phenomena.
- These findings provide insights into the complex regulation of immune cell signaling molecules.