Clostridium difficile toxin CDT hijacks microtubule organization and reroutes vesicle traffic to increase pathogen adherence

Schwan C, Kruppke AS, Nölke T, Schumacher L, Koch-Nolte F, Kudryashev M, Stahlberg H, Aktories K.

Proc Natl Acad Sci U S A. 2014 Feb 11;111(6):2313-8

Speaker: Bo-Yang Tsai (蔡博仰)                         Time: 13:10~14:00, Oct.8, 2014

Commentator: Dr. I-Hsiu Huang (黃一修老師)      Place: Room 601

Abstract:

         During the last decade, the emergence of hypervirulent strains of Clostridium difficile capable of expressing higher amount of Rho-inactivating toxin A and B has resulted in more severe symptoms during C. difficile infections. Additionally these strains produce an actin-ribosylating toxin C. difficile transferase (CDT) that can inhibit actin polymerization. In author's previous study, they found that CDT-induced depolymerization of F-actin resulted in the formation of long microtubule-based protrusion which enhanced bacteria adherence.[1] Here, the authors want to know the mechanism of CDT-induced adherence enhancement. First using the Cryo-EM and ER-GFP to observe the content of protrusion and the images showed that it contains ER tubules and vesicles. Previous study had demonstrated that ER interact with microtubule via Stim1, which is a Ca⁺² sensor in the ER membrane and interact with plasma membrane Oria1 activating the store-operated calcium entry (SOCE).[2] And other paper indicated that the rapid increase in intracellular Ca⁺² directly triggers the regulated exocytosis.[3]Therefore the authors wanted to known whether Stim1 is involved in CDT-induced ER translocation and affect the Ca⁺² signaling. Knockdown of Stim1 reduced the formation of ER-containing protrusions and strongly blocked the CDT-induce SOCE enhancement. In line with these finding, Stim1 was found to be involved in CDT-induced ER remodeling and SOCE enhancement. Further the authors asked whether CDT alter the vesicle trafficking and secretion of host factor resulting in bacteria adherence enhancement. To this end the authors used the vesicle trafficking inhibitor BFA and found it reduced CDT-induced adherence, suggesting an involvement of trafficking system. Using fluorescent Rab11 constructs and HiLyte488-labeledfibronection, the authors further showed that CDT induce Rab11-mediated fibronectin-containing vesicles redistribution from the basolateral side to the apical side and accumulate on the protrusion, eventually resulting in enhancement of bacteria adherence. Finally the authors test a functional connection between SOCE and secretion of fibronection by using the SOCE inhibitor 2-APB which caused a reduction of CDT-induced secretion and fibronection redistribution. Similarly, knockdown of Stim1 also caused stronger reduction of fibronectin redistribution. In conclusion, C. difficile adherence can be regulated by CDT-induced fibronection redistribution via Stim1-dependent Ca⁺² signaling.

References:

1.    Aktories, K., et al., Actin as target for modification by bacterial protein toxins. FEBS J, 2011. 278(23): p. 4526-43.

2.    Grigoriev, I., et al., STIM1 is a MT-plus-end-tracking protein involved in remodeling of the ER. Curr Biol, 2008. 18(3): p. 177-82.

3.    Barclay, J.W., A. Morgan, and R.D. Burgoyne, Calcium-dependent regulation of exocytosis. Cell Calcium, 2005. 38(3-4): p. 343-53.