Bacterial toxins are the causative agents for a variety of human diseases. However, the molecular basis of infection, in many cases, remains enigmatic. Cholera toxin (CT) produced by Vibrio cholerae is the virulence factor responsible for massive secretory diarrhea. As this disease remains a global health issue, elucidating its basic mechanism of action is paramount. To intoxicate cells, CT is transported from the cell surface to the lumen of the endoplasmic reticulum (ER). In this compartment, the toxic CTA1 fragment of CT disguises as a misfolded protein and hijacks the cellular machinery that normally moves misfolded proteins from the ER into the cytosol for degradation by the proteasome. Upon reaching the cytosol, CTA1 however escapes proteasomal destruction and triggers a signaling cascade that leads to pathologic water secretion (i.e. diarrhea), which can lead to death in severe cases. How CTA1 is transferred from the ER into the cytosol, a decisive intoxication step, remains poorly understood. In this application, we intend to address this question by using a combination of biochemical and cell biological approaches. Historically, studies on pathogen-host cell interactions have expounded on basic cellular processes. Moreover, these findings often led to the identification of key molecular targets amenable for therapeutic intervention. Thus we anticipate that our findings are likely to reveal novel mechanisms of protein transport across biological membranes and to identify new cellular factors that may serve as viable therapeutic targets. In addition, as other toxins such as ricin and shiga toxin also undergo ER-to-cytosol transport to induce cytotoxicity, our results should provide insights into their mechanism of action as well.

Public Health Relevance

Cholera toxin (CT) causes pathologic water secretion (i.e. diarrhea) in animals, which can lead to death in severe cases. A decisive step in the toxin-dependent infection process is transport of the toxin across the membrane of a sub-cellular compartment known as the endoplasmic reticulum (ER). However, the molecular details by which CT penetrate the ER membrane is not clear. We intend to clarify these processes in this application.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Host Interactions with Bacterial Pathogens Study Section (HIBP)
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Hall, Robert H
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University of Michigan Ann Arbor
Anatomy/Cell Biology
Schools of Medicine
Ann Arbor
United States
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Qi, Ling; Tsai, Billy; Arvan, Peter (2017) New Insights into the Physiological Role of Endoplasmic Reticulum-Associated Degradation. Trends Cell Biol 27:430-440
Walczak, Christopher Paul; Ravindran, Madhu Sudhan; Inoue, Takamasa et al. (2014) A cytosolic chaperone complexes with dynamic membrane J-proteins and mobilizes a nonenveloped virus out of the endoplasmic reticulum. PLoS Pathog 10:e1004007
Bernardi, Kaleena M; Williams, Jeffrey M; Inoue, Takamasa et al. (2013) A deubiquitinase negatively regulates retro-translocation of nonubiquitinated substrates. Mol Biol Cell 24:3545-56
Moore, Paul; He, Kaiyu; Tsai, Billy (2013) Establishment of an in vitro transport assay that reveals mechanistic differences in cytosolic events controlling cholera toxin and T-cell receptor ? retro-translocation. PLoS One 8:e75801
Williams, Jeffrey M; Inoue, Takamasa; Banks, Lindsey et al. (2013) The ERdj5-Sel1L complex facilitates cholera toxin retrotranslocation. Mol Biol Cell 24:785-95
Inoue, Takamasa; Tsai, Billy (2013) How viruses use the endoplasmic reticulum for entry, replication, and assembly. Cold Spring Harb Perspect Biol 5:a013250
Walczak, Christopher P; Bernardi, Kaleena M; Tsai, Billy (2012) Endoplasmic reticulum-dependent redox reactions control endoplasmic reticulum-associated degradation and pathogen entry. Antioxid Redox Signal 16:809-18