INTERFERON-GAMMA INDUCES CATHEPSIN-B EXPRESSION IN A HUMAN MACROPHAGE-LIKE CELL-LINE BY INCREASING BOTH TRANSCRIPTION AND MESSENGER-RNA STABILITY

We have demonstrated previously that treatment of the phorbol ester PM A-primed THP-1 human macrophagelike cells with interferon-gamma (IFN-g amma) in vitro induced time and dose-dependent increases in steady-sta te levels of cathepsin B (CB) mRNA. The present study was undertaken t o investigate the mechanism of that increase. In vitro nuclear transcr iption (nuclear run-off) assays of CB gene expression were performed w ith purified nuclei from IFN-gamma-treated or untreated THP-1 cells. T hese assays showed transcription to be increased approximately three-f old by IFN-gamma in the PMA-primed THP-1 cells. Studies with alpha-ama nitin indicated that the half-life of CB mRNA is prolonged after PMA a nd IFN-gamma treatment, by more than 90%. Therefore, the elevated CB m RNA level results from a combination of IFN-gamma-induced increase in the transcription rate of the CB gene and stabilization of the corresp onding transcripts. The IFN-gamma-mediated increase in CB gene transcr iption and steady-state mRNA level was blocked by alpha-amanitin or cy cloheximide, suggesting the involvement of RNA polymerase II and the r equirement of de novo protein synthesis.