Related Experiment Videos
IL-1 secretion by macrophages. Enhancement of IL-1 secretion and processing by calcium ionophores
J Suttles1, J G Giri, S B Mizel
1Department of Microbiology and Immunology, Wake Forest University Medical Center, Winston-Salem, NC 27103.
Abstract:
In the present study we have demonstrated that the murine IL-1 alpha precursor lacks a cleavable signal sequence and does not undergo cotranslational translocation across microsomal membranes in vitro. Culture supernatants of the murine macrophage cell line, P388D, or from normal peritoneal macrophages collected within 0.5 to 3 h after stimulation contained the 33,000 m.w. precursor as the predominant form of IL-1 alpha. Over an 18-h period, the level of low m.w. IL-1 alpha increased as the secreted precursor was processed by extracellular and/or cell surface-associated proteolytic enzymes. The calcium ionophores A23187 and ionomycin were found to dramatically enhance the release and processing of murine and human IL-1. The rapid release of IL-1 in response to a change in the intracellular level of calcium does not appear to be caused by release of a membrane-bound form of the protein, nor is there evidence that IL-1 is packaged and released from cytoskeletal associated secretory granules. In marked contrast, calcium ionophores do not induce secretion of IL-1 from a nonmacrophage cell line that synthesizes but does not normally secrete IL-1. Our results suggest that activated macrophages possess a novel processing independent, possibly calcium-dependent, mechanism that allows for the release of the precursor forms of IL-1 alpha and IL-1 beta.
Insights
Activated macrophages release precursor Interleukin-1 (IL-1) via a novel calcium-dependent pathway, independent of traditional secretion. This mechanism bypasses standard processing, enabling rapid IL-1 release.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Interleukin-1 (IL-1) is a key cytokine involved in inflammation and immunity.
- The secretion pathway of IL-1, particularly its precursor form, has been a subject of research.
- Understanding IL-1 release mechanisms is crucial for developing targeted immunotherapies.
Purpose of the Study:
- To investigate the mechanism of Interleukin-1 alpha (IL-1 alpha) precursor release from macrophages.
- To determine the role of calcium signaling in IL-1 secretion.
- To elucidate the processing and release kinetics of IL-1 alpha.
Main Methods:
- In vitro translocation assays using microsomal membranes.
- Analysis of culture supernatants from macrophage cell lines (P388D) and primary macrophages.
- Treatment with calcium ionophores (A23187, ionomycin) to assess IL-1 release and processing.
- Comparison with a non-macrophage cell line.
Main Results:
- Murine IL-1 alpha precursor lacks a signal sequence and does not undergo cotranslational translocation.
- The predominant form of IL-1 alpha in early culture supernatants is the 33,000 m.w. precursor.
- Extracellular and cell surface proteases process the precursor into lower molecular weight forms over time.
- Calcium ionophores significantly enhance the release and processing of both murine and human IL-1.
- IL-1 release is rapid and calcium-dependent, not involving membrane-bound forms or secretory granules.
- Calcium ionophores do not induce IL-1 secretion in non-macrophage cell lines.
Conclusions:
- Activated macrophages utilize a unique, processing-independent, calcium-dependent mechanism for releasing IL-1 alpha and IL-1 beta precursors.
- This pathway differs from conventional secretory pathways and does not rely on signal sequences or secretory granules.
- The findings shed light on a novel aspect of cytokine regulation in immune responses.