ENDOTOXIN INDUCES INCREASED INTRACELLULAR CATHEPSIN-B ACTIVITY IN THP-1 CELLS

Macrophage cathepsin B (CB) is implicated in tissue injury in inflamma tory diseases. Lipopolysaccharide (LPS) is an activator of macrophages whose effect on CB is unknown. This study was undertaken to investiga te the potential of macrophages as a source of increased CB and to det ermine if exposure to LPS might stimulate CB levels. As a model we cho se the macrophage-like tumor line, THP-1. Incubation with LPS led to a time and dose-dependent increase in CB activity. LPS potentiated inte rferon-gamma (IFN-gamma)-induced elevations of CB and led to an additi ve increase in CB activity. Pretreatment of the cells with LPS not onl y caused a marked stimulation of CB activity over that seen with IFN-g amma alone, but also decreased the concentration and exposure time to the cytokine necessary to achieve maximum induction of the enzyme. The LPS and IFN-gamma induced CB increases were abolished by cycloheximid e or actinomycin D in the cultures, indicating that the increases in C B required increased RNA transcription and de novo protein synthesis. Direct measurement of CB mRNA showed increases. These data indicate th at although LPS alone appears to induce the production of CB in THP-1 cells, it augments IFN-gamma induced increases, suggesting that two si gnals are necessary for maximum CB induction in this system.