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Cholera toxin activates the unfolded protein response through an adenylate cyclase-independent mechanism

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Date Issued:
2013
Abstract/Description:
Cholera toxin (CT) is a bacterial protein toxin responsible for the gastrointestinal disease known as cholera. CT stimulates its own entry into intestinal cells after binding to cell surface receptors. Once internalized, CT is delivered via vesicle-mediated transport to the endoplasmic reticulum (ER), where the CTA1 subunit dissociates from the rest of the toxin and is exported (or translocated) into the cytosol. CTA1 translocates from the ER lumen into the host cytosol by exploiting a host quality control mechanism called ER-associated degradation (ERAD) that facilitates the translocation of misfolded proteins into the cytosol for degradation. Cytosolic CTA1, however, escapes this fate and is then free to activate its target, heterotrimeric G-protein subunit alpha (Gs?), leading to adenlyate cyclase (AC) hyperactivation and increased cAMP concentrations. This causes the secretion of chloride ions and water into the intestinal lumen. The result is severe diarrhea and dehydration which are the major symptoms of cholera. CTA1's ability to exploit vesicle-mediated transport and ERAD for cytosolic entry demonstrates a potential link between cholera intoxication and a separate quality control mechanism called the unfolded protein response (UPR), which up-regulates vesicle-mediated transport and ERAD during ER stress. Other toxins in the same family such as ricin and Shiga toxin were shown to regulate the UPR, resulting in enhanced intoxication.Here, we show UPR activation by CT, which coincides with a marked increase in cytosolic CTA1 after 4 hours of toxin exposure. Drug induced-UPR activation also increases CTA1 delivery to the cytosol and increases cAMP concentrations during intoxication. We investigated whether CT stimulated UPR activation through Gs? or AC. Chemical activation of Gs? induced the UPR and increased CTA1 delivery to the cytosol. However, AC activation did not increase cytosolic CTA1 nor did it activate the UPR. These data provide further insight into the molecular mechanisms that cause cholera intoxication and suggest a novel role for Gs? during intoxication, which is UPR activation via an AC-independent mechanism.
Title: Cholera toxin activates the unfolded protein response through an adenylate cyclase-independent mechanism.
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Name(s): Vanbennekom, Neyda, Author
Teter, Kenneth, Committee Chair
Tatulian, Suren, Committee Member
Jewett, Mollie, Committee Member
Zervos, Antonis, Committee Member
University of Central Florida, Degree Grantor
Type of Resource: text
Date Issued: 2013
Publisher: University of Central Florida
Language(s): English
Abstract/Description: Cholera toxin (CT) is a bacterial protein toxin responsible for the gastrointestinal disease known as cholera. CT stimulates its own entry into intestinal cells after binding to cell surface receptors. Once internalized, CT is delivered via vesicle-mediated transport to the endoplasmic reticulum (ER), where the CTA1 subunit dissociates from the rest of the toxin and is exported (or translocated) into the cytosol. CTA1 translocates from the ER lumen into the host cytosol by exploiting a host quality control mechanism called ER-associated degradation (ERAD) that facilitates the translocation of misfolded proteins into the cytosol for degradation. Cytosolic CTA1, however, escapes this fate and is then free to activate its target, heterotrimeric G-protein subunit alpha (Gs?), leading to adenlyate cyclase (AC) hyperactivation and increased cAMP concentrations. This causes the secretion of chloride ions and water into the intestinal lumen. The result is severe diarrhea and dehydration which are the major symptoms of cholera. CTA1's ability to exploit vesicle-mediated transport and ERAD for cytosolic entry demonstrates a potential link between cholera intoxication and a separate quality control mechanism called the unfolded protein response (UPR), which up-regulates vesicle-mediated transport and ERAD during ER stress. Other toxins in the same family such as ricin and Shiga toxin were shown to regulate the UPR, resulting in enhanced intoxication.Here, we show UPR activation by CT, which coincides with a marked increase in cytosolic CTA1 after 4 hours of toxin exposure. Drug induced-UPR activation also increases CTA1 delivery to the cytosol and increases cAMP concentrations during intoxication. We investigated whether CT stimulated UPR activation through Gs? or AC. Chemical activation of Gs? induced the UPR and increased CTA1 delivery to the cytosol. However, AC activation did not increase cytosolic CTA1 nor did it activate the UPR. These data provide further insight into the molecular mechanisms that cause cholera intoxication and suggest a novel role for Gs? during intoxication, which is UPR activation via an AC-independent mechanism.
Identifier: CFE0004951 (IID), ucf:49560 (fedora)
Note(s): 2013-08-01
M.S.
Medicine, Molecular Biology and Microbiology
Masters
This record was generated from author submitted information.
Subject(s): cholera toxin -- adenylate cyclase -- G protein -- CTA1 -- unfolded protein response -- intoxication
Persistent Link to This Record: http://purl.flvc.org/ucf/fd/CFE0004951
Restrictions on Access: campus 2014-08-15
Host Institution: UCF

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