Shiga toxin-1 regulation of cytokine production by human proximal tubule cells.
BACKGROUND
Interleukin-1 (IL-1), interleukin-6 (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-1 (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-1, 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
Stx-1 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-1 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.
Veterans Affairs Medical Center and the University of Utah School of Medicine, Salt Lake City 84148, USA.
A K
AK
Hughes
P K
PK
Stricklett
D E
DE
Kohan
D001427:Bacterial Toxins / Q000633:toxicity*; D001483:Base Sequence; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D003513:Cycloheximide / Q000633:toxicity; D016207:Cytokines / Q000096:biosynthesis* / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D006463:Hemolytic-Uremic Syndrome / Q000209:etiology / Q000235:genetics / Q000503:physiopathology; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D007375:Interleukin-1 / Q000096:biosynthesis / Q000235:genetics; D015850:Interleukin-6 / Q000096:biosynthesis / Q000235:genetics; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000502:physiology*; D008070:Lipopolysaccharides / Q000633:toxicity; D014176:Protein Biosynthesis; D011500:Protein Synthesis Inhibitors / Q000633:toxicity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D022603:Shiga Toxins; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000235:genetics
D001427:Bacterial Toxins; D016207:Cytokines; D017931:DNA Primers; D018836:Inflammation Mediators; D007375:Interleukin-1; D015850:Interleukin-6; D008070:Lipopolysaccharides; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D022603:Shiga Toxins; D014409:Tumor Necrosis Factor-alpha; D003513:Cycloheximide