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Induction of metallothionein by a macrophage factor and the partial characterization of the factor
Abstract:
The mechanism of metallothionein (MT) induction by lipopolysaccharide (LPS) was studied using an in vitro system. Rat peritoneal macrophages were incubated with or without LPS, after which the incubation medium was overlaid on human hepatic (Chang) cells. MT synthesis was induced in Chang cells treated with the macrophage medium incubated with LPS. No induction was observed when LPS was added directly to the Chang cell medium or when Chang cells were treated with the macrophage medium incubated without LPS. These results suggest that induction of MT by LPS is mediated by a factor released from macrophages. The factor is different from the known primary inducers of MT, such as heavy metals, glucocorticoid hormones, interleukin 1, and interferon. The factor is heat stable, nondialyzable, and stable at pH 2. Although its activity is lost by pepsin and trichloroacetic acid, it is resistant to trypsin.
Insights
Lipopolysaccharide (LPS) induces metallothionein (MT) via a heat-stable factor released by macrophages, not directly. This macrophage-derived factor is crucial for MT synthesis in hepatic cells.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Metallothionein (MT) are cysteine-rich proteins known to bind heavy metals.
- Lipopolysaccharide (LPS), a component of Gram-negative bacteria, can induce various cellular responses.
- The precise mechanism of MT induction by LPS, particularly involving cellular interactions, requires further elucidation.
Purpose of the Study:
- To investigate the in vitro mechanism by which lipopolysaccharide (LPS) induces metallothionein (MT) synthesis.
- To determine if LPS directly induces MT in hepatic cells or if it requires mediation by other cell types.
Main Methods:
- An in vitro system using rat peritoneal macrophages and human hepatic (Chang) cells was employed.
- Macrophages were incubated with or without LPS, and the resulting medium was applied to Chang cells.
- Characterization of the inducing factor's stability (heat, dialysis, pH, enzymatic digestion) was performed.
Main Results:
- MT synthesis was induced in Chang cells when treated with medium from LPS-exposed macrophages.
- Direct addition of LPS to Chang cells or treatment with medium from unexposed macrophages did not induce MT.
- The inducing factor is heat-stable, nondialyzable, stable at pH 2, pepsin-sensitive, and trypsin-resistant.
Conclusions:
- LPS-induced MT synthesis in hepatic cells is mediated by a soluble factor released from macrophages.
- This macrophage-derived factor is distinct from known primary MT inducers like heavy metals and cytokines.
- The factor's biochemical properties suggest it is a peptide or protein with specific stability characteristics.