Host-derived Extracellular Trypsin Primes Shiga toxin 2a for Enhanced Intoxication with Reduced Dependence on Retrograde Trafficking

Hemolytic uremic syndrome is a complication of STEC infections. Although canonical Stx intoxication was known to depend upon retrograde trafficking to the Golgi apparatus and endoplasmic reticulum, the impact of extracellular proteolytic priming on the retrograde pathway remained poorly defined. In this study, we showed that the extracellular trypsin cleavage of Stx2a was associated with enhanced cytotoxicity and reduced sensitivity to inhibition of the canonical retrograde pathway. Proteolytically processed Stx2a had increased cytotoxicity in cells expressing globotriaosylceramide (Gb3) receptor compared to its non-processed counterpart, suggesting that receptor dependency is retained after proteolytic priming. Compared with intact Stx2a, the proteolyzed form retained substantial cytotoxicity under pharmacologic inhibition of retrograde trafficking and remained sensitive to perturbation of thiol reduction and Hsp70 function. Importantly, Stx2a exposure increased extracellular trypsin levels in association with IL-1β/IL-6 signaling and NLRP3/caspase activity, consistent with a cytokine–trypsin amplification loop. In vivo, proteolyzed Stx2a caused enhanced mortality, acute kidney injury, and injury-related gene expression changes relative to native Stx2a. These findings support trypsin-mediated extracellular proteolytic priming as a host-associated determinant of Stx2a pathogenicity and HUS progression.