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Expression of the complement C8 genes during interleukin-6-mediated in vitro induction of the acute-phase response
G F Späth1, G Ramadori, C Rittner
1Institute of Legal Medicine, Johannes Gutenberg University, Mainz, Germany.
Insights
Human complement component C8 (C8) is a positive acute-phase protein. Interleukin-6 (IL-6) induces C8 expression in HepG2 cells, with evidence of post-transcriptional regulation for the C8 beta subunit.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- The human complement component C8 comprises alpha, beta, and gamma chains encoded by distinct genes.
- C8A and C8B genes are located on chromosome 1p, while C8G is on chromosome 9q.
- Understanding C8 biosynthesis and regulation is crucial for complement system research.
Purpose of the Study:
- To investigate the biosynthesis and regulation of human complement component C8.
- To determine if interleukin-6 (IL-6) influences C8 expression in vitro.
- To elucidate the regulatory mechanisms of C8 gene products.
Main Methods:
- Utilized the human hepatoma cell line HepG2 for in vitro studies.
- Induced the acute-phase response using the cytokine IL-6.
- Analyzed C8 subunit expression via immunoprecipitation and SDS-PAGE of biosynthetically labeled proteins.
Main Results:
- C8 expression, including alpha-gamma and beta subunits, showed a positive response to IL-6 induction.
- C8 was characterized as a positive acute-phase protein in vitro in HepG2 cells.
- Evidence suggests post-transcriptional regulation of the C8 beta subunit, based on transcript comparisons.
Conclusions:
- Human complement component C8 functions as a positive acute-phase protein.
- IL-6 is a significant inducer of C8 expression in HepG2 cells.
- Post-transcriptional mechanisms regulate the expression of the C8 beta subunit.
Abstract:
The three chains of the human complement component C8-alpha, beta and gamma- are encoded by distinct structural genes. C8A and C8B are closely linked on chromosome 1p and C8G is located on chromosome 9q. The biosynthesis and regulation of the gene products were studied in the human hepatoma-derived cell line HepG2 after in vitro induction of the acute-phase response by incubation with the cytokine interleukin IL-6. Analysis of C8 expression by immunoprecipitation and SDS-PAGE of biosynthetically labeled alpha-gamma and beta subunits demonstrated a positive response to this cytokine. The expression pattern observed in the hepatoma cells characterizes C8 in vitro as a positive acute-phase protein. In addition, the comparison of the relative amounts of the C8 transcripts provides evidence for a post transcriptional regulation of the C8 beta subunit. No evidence was obtained for an increased expression of IL-6 or IL-6 receptor mRNA thus excluding autoregulatory mechanisms of the cytokine in HepG2 cells.