Shiga toxin-1 regulation of cytokine production by human proximal tubule cells

Background. Interleukin-1 (IL-1), interleukin-h (IL-6), and tumor necrosis factor (TNF) levels are elevated in kidneys of patients with post-diarrheal hemolytic uremic syndrome (D + HUS) and may contribute to renal dysfunction. The renal cellular sources of these inflammatory cytokines in D + HUS are largely unknown, however, the proximal tubule has emerged as a potentially important candidate. Since Shiga toxin-l (Stx-1) has been implicated in the genesis of D + HUS, we examined the effect of Stx-1 on cytokine production by human proximal tubule cells. Methods. Stx-1 cytotoxicity, protein synthesis inhibition, and effect on IL-I, IL-6, and TNF protein release and mRNA levels were determined. The effect of another protein synthesis inhibitor, cycloheximide (CHX), on these parameters was also evaluated. Results. Sts-l greatly increased TNF release and mRNA levels while CHX, at concentrations that produced similar inhibition of protein synthesis. had no effect on TNF production. In contrast, Stx-1 and CHX caused comparable elevations in IL-1 release and mRNA accumulation. Stx-1 and CHX also stimulated IL-6 mRNA accumulation, but only at concentrations that either were cytotoxic or substantially blocked protein synthesis. Finally, lipopolysaccharide, which is likely to be elevated in the circulation of patients with D + HUS, had no effect alone, but synergized with Stx-1 to increase IL-I production. Conclusions. These results indicate that Stx-1 stimulates proximal tubule inflammatory cytokine production and that this effect is due partially to nonspecific induction of mRNA levels as well as activation of Stx-1-specific mechanisms.