Studies on Shiga toxin type 1 mediated tumor necrosis factor synthesis in a human monocytic cell line

Abstract

Shiga toxins (Stxs) have been implicated in the development of various human diseases associated with enterohemorrhagic Escherichia coli infections, the most common and serious being Hemolytic Uremic Syndrome (HUS). HUS continues to be a significant cause Of morbidity and mortality in many underdeveloped countries. HUS patients frequently show profound damage to the glomerular endothelial lining of the kidneyy where the cells appear swollen and detached from the basement membrane. However, in vitro studies have shown that a direct cYtOtOxic effect Of Purified stx on human vascular endothelial cells was minimal unless they were treated with proinflammatory cytokines like interleukin-I (IL-1) or tumor necrois factor (-rNF)-These cytokines have been shown to upregulate the expression of stx receptors, globotrioacylceramide (Gb3)-We show here that purified Stxl induces TNF secretion in THP-1 cells (a human monocytic cell line) in a dose and time dependent manner. E3oth Stx and LPS treatment resulted in increased TNF production in THP-1 cells. However, treatment with non-toxic B subunit pentamers of Stxl did not cause any significant increase in TNF production. Northern blot analysis showed that the Stxl mediated increase in TNF production is mediated at least in part by increased transcription of the TNF gene. PKC inhibitors, H-7 and K252a were able to block Stxl mediated increase in TNF production and MRNA synthesis, suggesting a possible role for PKC in Stxl mediated TNF production and TNF-(X MRNA synthesis. Further, measurement of PKC activity showed elevated levels in the presence of Stxl, which was totally blocked by H-7 and K252a.