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A new negatively regulated acute-phase phosphoprotein synthesized by rat hepatocytes
Abstract:
The effect of acute inflammation on the production of the major phosphorylated protein (PP63) excreted by rat hepatocytes was investigated. Both intra- and extracellular forms of the protein labelled with [32P]Pi, [3H]fucose and [35S]methionine were immunoprecipitated with monospecific polyclonal antibodies, and relative rates of PP63 synthesis were measured. The hepatocytes of acutely inflamed rats produced and excreted 85% less 32P- and 3H-labelled PP63 than did control cells. This decreased amount of PP63 did not result from an impairment in the phosphorylation or glycosylation processes or from a blockade in excretion, but rather was found to be due to extensive shut-off in biosynthesis of the protein as measured by [35S]methionine incorporation. Thus PP63 would appear to represent a new negatively regulated acute-phase protein.
Insights
Acute inflammation significantly reduces the production of phosphorylated protein 63 (PP63) in rat hepatocytes. This decrease stems from suppressed biosynthesis, identifying PP63 as a novel acute-phase protein.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Hepatocytes are key in producing proteins during inflammation.
- Phosphorylated protein 63 (PP63) is a major excreted protein by rat hepatocytes.
- The role of PP63 in the acute-phase response is not well understood.
Purpose of the Study:
- To investigate the effect of acute inflammation on PP63 production and excretion by rat hepatocytes.
- To determine the regulatory mechanisms underlying changes in PP63 levels during inflammation.
- To ascertain if PP63 functions as an acute-phase protein.
Main Methods:
- Rat hepatocytes were subjected to acute inflammation models.
- PP63, both intracellular and extracellular, was labeled with [32P]Pi, [3H]fucose, and [35S]methionine.
- Immunoprecipitation using monospecific polyclonal antibodies and measurement of protein synthesis rates were performed.
Main Results:
- Acutely inflamed rat hepatocytes produced and excreted 85% less 32P- and 3H-labeled PP63 compared to control cells.
- The reduction in PP63 was not due to impaired phosphorylation, glycosylation, or excretion.
- Decreased PP63 levels resulted from a significant shut-off in its biosynthesis, as indicated by [35S]methionine incorporation.
Conclusions:
- PP63 biosynthesis is extensively suppressed during acute inflammation in rat hepatocytes.
- PP63 exhibits characteristics of a negatively regulated acute-phase protein.
- These findings reveal a novel regulatory mechanism in the acute-phase response involving PP63.