Shiga toxin-induced tumor necrosis factor alpha expression: Requirement for toxin enzymatic activity and monocyte protein kinase C and protein tyrosine kinases

Infections with Shiga toxin (Stx)-producing bacteria cause bloody diarrhea which may progress to life-threatening complications, including acute renal failure and neurological abnormalities. The precise mechanism of disease p rogression is unclear, although evidence suggests that the localized produc tion of the host proinflammatory cytokines tumor necrosis factor alpha (TNF -alpha) and interleukin-1 may exacerbate toxin-mediated vascular damage. Pu rified Stxs have been demonstrated to elicit proinflammatory cytokine synth esis from human peripheral blood mononuclear cells and monocytic cell lines in vitro. To understand toxin-monocyte interactions required for cytokine synthesis, we have treated differentiated THP-1 cells with purified wild-ty pe toxins, enzymatic mutants, or B subunits and measured TNF-alpha producti on. Our data suggest that A subunit enzymatic activity is essential for cyt okine production. THP-1 cells were treated with a series of protein kinase C (PKC), PKA, and protein tyrosine kinase inhibitors to examine the role of intracellular signaling molecules in Stx-mediated cytokine production. Tre atment of cells with PKC and tyrosine kinase inhibitors blocked TNF-alpha s ecretion by Stx-stimulated THP-1 cells. Stx treatment directly activated PK C, which occurred at a point upstream of transcriptional activation of the gene encoding TNF-alpha.