Macrophage TNF mRNA expression is modulated by protease inhibitors

Nuclear factor kappa B (NF kappa B) is an important transcriptional activator protein and is a crucial component of the host's response to infection. The activation of NF kappa B is correlated with the phosphorylation of inhibitory kappa B (I kappa B) and its subsequent degradation. We hypothesized that protease inhibitors which prevented I kappa B degradation could inhibit the macrophage gene activation and reduce the production of inflammatory cytokines.

Rabbit alveolar macrophages (M phi) were obtained by bronchoalveolar lavage. M phi were exposed to Escherichia coli lipopolysaccharide (LPS) (10 ng/ml) in the presence of various concentrations of protease inhibitors, either N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) or N-benzoyl-L-tyrosine ethyl ester (BTEE). Total RNA was extracted for Northern blot assay of tumor necrosis factor (TNF) mRNA expression using a rabbit genomic DNA probe. Total nuclear extracts were also obtained for the measurement of the NF kappa B activity with the electrophoretic mobility shift assay. The TNF production in the M phi supernatant was measured by L929 bio-assays.

NF kappa B activity induced by LPS was inhibited by either BTEE or TPCK. Inhibition of NF kappa B activity by these agents also prevented TNF mRNA expression and TNF production induced by LPS. The cellular mechanism leading to NF kappa B activation was further studied. TNF mRNA expression and NF kappa B activation were inhibited by D609, a phospholipase C (PLC) inhibitor, as well as by protein kinase C (PKC) inhibitors. In addition, direct stimulation of PKC led to NF kappa B activation and TNF mRNA expression.

These data suggest that TNF mRNA expression of LPS-stimulated M phi is mediated through NF kappa B, NF kappa B activation is intimately regulated by the PLC signaling pathway.