Role of Phospholipase A2 in Retrograde Transport of Ricin

Abstract

Ricin is a protein toxin classified as a bioterror agent, for which there are no known treatment options available after intoxication. It is composed of an enzymatically active A-chain connected by a disulfide bond to a cell binding B-chain. After internalization by endocytosis, ricin is transported retrogradely to the Golgi and ER, from where the ricin A-chain is translocated to the cytosol where it inhibits protein synthesis and thus induces cell death. We have identified cytoplasmic phospholipase A2 (PLA2) as an important factor in ricin retrograde transport. Inhibition of PLA2 protects against ricin challenge, however the toxin can still be endocytosed and transported to the Golgi. Interestingly, ricin transport from the Golgi to the ER is strongly impaired in response to PLA2 inhibition. Confocal microscopy analysis shows that ricin is still colocalized with the trans-Golgi marker TGN46 in the presence of PLA2 inhibitor, but less is colocalized with the cis-Golgi marker GM130. We propose that PLA2 inhibition results in impaired ricin transport through the Golgi stack, thus preventing it from reaching the ER. Consequently, ricin cannot be translocated to the cytosol to exert its toxic action.

Exogenous lysophospholipids with large head groups perturb clathrin‐mediated endocytosis

“…It should be noted that HEp‐2 cells used in this study (ATCC CCL‐23) have been shown to have a similar karyotype to HeLa and HeLa S3 cells, and that our HEp‐2 and HeLa cells were profiled by short tandem repeat DNA analysis in March 2012 and found to be 86% and 94% identical to ATCC HeLa cells (ATCC CCL‐2), respectively. We have previously observed important differences between our HEp‐2 and HeLa cell lines, 27‐29 and we have therefore chosen to include both cell types in this study. As shown in Figure , treatment with 10 μM LPI clearly reduced Tf endocytosis in HEp‐2, HeLa and SUM‐159 cells, but had little or no effect in SK‐BR‐3, PC‐3 and U‐2 OS cells.…”

A Bispecific Antibody Promotes Aggregation of Ricin Toxin on Cell Surfaces and Alters Dynamics of Toxin Internalization and Trafficking

“…It is interesting to note that JNA6 neutralizes ricin in vitro , but does so without interfering with ricin trafficking to the TGN. JNA6 must, therefore, neutralize ricin by interfering with egress from TGN [ 44 ], transport to the ER [ 28 ], and/or retro-translocation [ 45 ].…”

Cytolethal Distending Toxin: A Unique Variation on the AB Toxin Paradigm

“…However, there is some data to suggest that phospholipase A2 contributes to the process [137,138]. Finally, ricin translocation to the cytosol may depend on sequences enriched in hydrophobic amino acids [139].…”