Ricin Inhibits Activation of the Unfolded Protein Response by Preventing Splicing of the HAC1 mRNA

Parikh, Bijal A.; Tortora, Andrew; Li, Xiao Ping; Tumer, Nilgun E.

doi:10.1074/jbc.m707981200

Cited by 34 publications

(45 citation statements)

References 42 publications

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“…The doubling time of cells expressing the A subunits of Stx1 and Stx2 was 13.3 h and 14.7h, respectively, while doubling time of cells harboring the empty vector ranged between 4.5–6 h (Table 1). As previously observed with RTA (Li et al, 2007; Parikh et al, 2008), the majority of Stx1A and Stx2A expressed in yeast was associated with the membrane fraction by immunoblot analysis (Fig. 2A).…”

Section: Resultssupporting

confidence: 84%

Identification of amino acids critical for the cytotoxicity of Shiga toxin 1 and 2 in Saccharomyces Cerevisiae

Kyu

Shete

et al. 2011

Toxicon

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Shiga toxins (Stx1 and Stx2) are produced by E. coli O157:H7, which is a leading cause of foodborne illness. The A subunits of Stx1 (Stx1A) and Stx2 (Stx2A) are ribosome inactivating proteins (RIPs) that inhibit translation by removing an adenine from the highly conserved α-sarcin ricin loop (SRL) of the large rRNA. Here, we used mutagenesis in S. cerevisiae to identify residues critical for cytotoxicity of Stx1A and Stx2A. The A subunits depurinated the SRL, inhibited translation and caused apoptotic-like cell death in yeast. Single mutations in Asn75, Tyr77, Glu167 and Arg176 reduced the cytotoxicity of both toxins around 10-fold. However, Asn75 and Tyr77 were more critical for the depurination activity of Stx2A, while Arg176 was more critical for the depurination activity of Stx1A. The crystal structures of the two proteins lack electron density for some surface loops, including one which is adjacent to the active site in both molecules. Modeling these loops changed neither the secondary nor the tertiary structures of the rest of the protein. Analysis of solvent accessible surface areas indicated that Asn75 and Tyr77 are more exposed in Stx2A, while Arg176 is more exposed in Stx1A, indicating that residues with higher surface exposure were more critical for enzymatic activity. Double mutations at Glu167 and Arg176 eliminated the depurination activity and cytotoxicity of both toxins. C-terminal deletions of A chains eliminated cytotoxicity of both toxins, but showed functional differences. Unlike Stx1A, cytotoxicity of Stx2A was lost before its ability to depurinate ribosomes. These results identify residues that affect enzymatic activity and cytotoxicity of Stx1A and Stx2A differently and demonstrate that the function of these residues can be differentiated in yeast. The extent of ribosome depurination and translation inhibition did not correlate with the extent of cell death, indicating that depurination of the SRL and inhibition of translation are not entirely responsible for cell death.

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Section: Resultssupporting

confidence: 84%

Identification of amino acids critical for the cytotoxicity of Shiga toxin 1 and 2 in Saccharomyces Cerevisiae

Kyu

Shete

et al. 2011

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“…The third signaling pathway, which involves splicing of XBP-1 by IRE1, was not activated after exposure to RIPs. That coincides with a study in yeast that revealed the inhibition of the XBP-1 homologue Hac1 by ricin A-chain [30]. The assumption that splicing of XBP-1 is inhibited by RIPs is confirmed by the observation that many chaperones that are dependent on spliced XBP-1, like EDEM1, RAMP4 and HEDJ, were not found upregulated at the RNA level (Table 1).…”

Section: Discussionsupporting

confidence: 55%

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

Horrix

Raviv

Flescher

et al. 2010

Cell. Mol. Life Sci.

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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.

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“…RTA could potentially activate the UPR, which could contribute to its apoptotic effects. However, results of another study found that RTA alone failed to activate either the IRE1/XBP1 or the PERK/eIF2-α sensors of the UPR pathway [189]. This agrees with studies in yeast [188].…”

Section: Action Of Ricin and Corresponding Immunotoxins On Ribosomes mentioning

confidence: 64%

Ricin and Ricin-Containing Immunotoxins: Insights into Intracellular Transport and Mechanism of action in Vitro

Słomińska-Wojewódzka

Sandvig

2013

Antibodies

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Ricin is a type II ribosome inactivating protein (RIP) isolated from castor beans. Its high toxicity classifies it as a possible biological weapon. On the other hand, ricin linked to specific monoclonal antibodies or used in other conjugates has powerful medical applications. Ricin consists of an A-chain (RTA) that damages ribosomes and inhibits protein synthesis, and a B-chain that plays a role in binding and cellular uptake. A number of recent studies have demonstrated that ricin-induced inhibition of protein synthesis is not the only mechanism responsible for cell death. It turns out that ricin is able to induce apoptosis in different cell lines and multiple organs in animals. However, the molecular link between protein synthesis inhibition and ricin-dependent triggering of apoptotic cell death is unclear. This review describes the intracellular transport of ricin and ricin-based immunotoxins and their mechanism of action in different non-malignant and cancer cell lines. Moreover, various ricin-containing immunotoxins, their composition, medical applications and side-effects will be described and discussed. Understanding the mechanism of action of ricin-based immunotoxins will facilitate construction of effectively acting immunotoxins that can be used in the clinic for cancer treatment

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Ricin Inhibits Activation of the Unfolded Protein Response by Preventing Splicing of the HAC1 mRNA

Cited by 34 publications

References 42 publications

Identification of amino acids critical for the cytotoxicity of Shiga toxin 1 and 2 in Saccharomyces Cerevisiae

Identification of amino acids critical for the cytotoxicity of Shiga toxin 1 and 2 in Saccharomyces Cerevisiae

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

Ricin and Ricin-Containing Immunotoxins: Insights into Intracellular Transport and Mechanism of action in Vitro

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