Destabilization of IL-8 mRNA by Anthrax Lethal Toxin: Demonstration of the Requirement for TTP and Examination of its Cellular Interactions

Control of mRNA stability is an important aspect in the regulation of gene expression. A well studied signal for rapid transcript decay in mammalian cells is the AU-rich element (ARE), which is found in the 3’ untranslated region (UTR) of many labile transcripts. These sequence elements confer destabilization of transcripts by binding to AU-binding proteins (AUBPs) that can recruit cellular decay enzymes. The stability of ARE-containing mRNAs can be regulated by extracellular stimuli, which allows for cells to adapt to the changing environment. AREs are found in many transcripts that encode for inflammatory genes, including TNF, GM-CSF, and IL-8. Pathogens evolve and devise mechanisms to subvert the immune response of the host to aid in its infection. Bacillus anthracis is one such infectious agent that can disable numerous arms of the host immune response. Its secreted toxin, anthrax lethal toxin (LeTx), causes the accelerated decay of the IL-8 mRNA. IL-8 is a dual function cytokine and chemokine that can recruit and activate neutrophils at the site of infection. Through the inactivation of MAPK pathways, LeTx activity causes the destabilization of IL-8 transcripts through its ARE. In this thesis, I show that an AUBP, TTP, is dephosphorylated by LeTx and MAPK inhibitors, and knock-down of its expression stabilized IL-8 transcripts. LeTx activity also increased the colocalization of TTP to P-bodies, cytoplasmic sites concentrated with RNA decay enzymes. This suggests that the post-translational modification of TTP induced by LeTx led to its enhanced destabilization function. Identified TTP-associated proteins, non-muscle myosin heavy chain 9 (myosin-9) and HSC-70, were examined for their role in IL-8 transcript decay. Knock-down of each protein led to a slower rate of IL-8 mRNA destabilization. However, treatment of LeTx continued to mediate accelerated destabilization of IL-8 in these siRNA-transfected cells. This suggests that LeTx, myosin-9, and HSC-70 modulate the destabilization function of TTP independently.

Department dc:contributor.department

Laboratory Medicine and Pathobiology

Year dc:date.issued

2012

Author dc:creator

• Chow, Man Chi Edith

Advisor dc:contributor.advisor

• Mogridge, Jeremy

• Anthrax lethal toxin
• mRNA destabilization
• Tristetraprolin

Statement dc:rights

• Attribution-NonCommercial-NoDerivs 3.0 Unported

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/3.0/

Language dc:language.iso

en_ca

Handle dc:identifier.uri

http://hdl.handle.net/1807/33880

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/33880