Plant ribosome-inactivating proteins type II induce the unfolded protein response in human cancer cells

Abstract

Cytotoxic ribosome-inactivating proteins (RIPs) of type II such as ricin were investigated as anti-cancer agents, but also pose a threat as biological weapons. The molecular mechanism leading to their toxic effects is, however, not yet clear. The current paradigm, which states that the irreversible depurination of 28S rRNA results in a general translational arrest eventually leading to cell death, has been questioned. Using micro-array, qRT-PCR and Western blot, we identified the unfolded protein response (UPR), a cellular mechanism activated in response to endoplasmic reticulum stress, that is induced in HCT116 and MDA-MB-231 cells exposed to the plant type II RIPs ricin, riproximin and volkensin. Apoptosis was induced by concentrations at which translation of UPR-related genes still occurred, despite concomitant ribosomal depurination. We conclude that UPR induction represents a model that better describes the cellular effects of RIP exposure at concentrations at which selected proteins are translated despite ribosomal depurination.

Evaluation of Riproximin Binding Properties Reveals a Novel Mechanism for Cellular Targeting

“…For aBSM, a molecular mass of 400 kDa was assumed (25,26). 920 GalNAc residues/molecule were estimated for aBSM based on data available for porcine submaxillary mucin, which possesses a molecular mass of 10 6 Da with ϳ2300 GalNAc residues/molecule (20).…”

“…Within the cell, the A-chain, an rRNA N-glycosidase, depurinates the 28S RNA, leading to transcriptional arrest and eventually cell death (5). Recently, it was shown that the mode of action also involves the induction of the unfolded protein response (6).…”

Riproximin’s activity depends on gene expression and sensitizes PDAC cells to TRAIL

“…5 The high toxicity after internalization of these RIPs is related to cell death resulting from apoptosis induction. [6][7][8] Pancreatic ductal adenocarcinoma (PDAC) has one of the worst survival rates of all malignancies. Despite continued efforts over the past decades to improve diagnosis and treatment, the prognosis of patients with PDAC is still poor, and incidence rates are virtually identical to mortality rates.…”

“…The differential sensitivity to Rpx observed in our panel of cell lines caused us to relate the expression profile of these cells with their sensitivity to Rpx. The lectin's potential to induce apoptosis 8 was then basis to monitor the expression of apoptosis related genes in PDAC cells following Rpx treatment. The modulation of gene expression observed in this experiment prompted the choice of TRAIL as combination partner of Rpx, and this combination showed synergistic antiproliferative activity.…”

A foresight study on emerging technologies: State of the art of Omics technologies and potential applications in food and feed safety

“…Horrix et al (2011) Bhaskar et al (2012) have examined both dose and time-dependent transcriptional responses induced by abrin in the adult mouse brain. Swiss albino mice (two experimental groups of 6 animals each) were exposed to 1 (2.83 μg/kg) and 2 LD 50 dose of abrin (5.66 μg/kg body weight) by intra-peritoneal route.…”