Gut pathogens deploy anti-apoptotic pathway to maintain infectious foothold in their host

Dr. Sharanya Chatterjee’s interview with Bio Patrika hosting “Vigyan Patrika”, a series of author interviews. Dr. Chatterjee is currently working as a postdoctoral researcher in the Centre for Molecular Bacteriology and Infection, Imperial College London with Prof. Gad Frankel. She obtained her M.Sc. degree from Department of Molecular Biology and Biotechnology, Tezpur University, Assam. She did her Ph.D. under the supervision of Prof. Utpal Tatu, Department of Biochemistry, Indian Institute of Science, Bangalore. During her Ph.D., she reported the misdiagnosis of a multidrug resistant fungal pathogen Candida auris. She did the first draft genome of the pathogen and also developed a PCR based diagnostic method to accurately identify it. Further she also worked extensively on heat shock proteins in fungal pathogens such as Candida albicans and Cryptococcus neoformans. She published her research findings in three articles: “Draft genome of a commonly misdiagnosed multidrug resistant pathogen Candida auris” in BMC genomics (2015), “Heat shock protein 90 localizes to the surface and augments virulence factors of Cryptococcus neoformans” in Plos Neglected Tropical Diseases (2017) and “Structural basis for species-selective targeting of Hsp90 in a pathogenic fungus” in Nature Communications (2019). Her recent work on a bacterial effector protein of enterohaemorrhagic Escherichia coli and related pathogens was published in Cellular Microbiology.

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How would you explain your paper’s key results to the non-scientific community?

Many enteric pathogens employ a needle-like apparatus called the type III secretion system (T3SS) to translocate bacterial proteins called effectors directly into the host cell cytoplasm. Once inside the cell, these effectors subvert signalling pathways of the intestinal epithelium, which enables enteric pathogens to successfully establish their infective niche within the human host. However, in doing so, some effectors can also trigger inflammatory pathways in the host cell, leading to death of the infected cells. Thus, the pathogen can become a victim of its own success, unless it finds a way to circumvent this.

The T3SS effectors EspO of enterohaemorrhagic Escherichia coli and Citrobacter rodentium, OspE of Shigella flexneri and SopO of Salmonella enterica Serovar Typhimurium were known to interact with integrin-linked kinase and localise to focal adhesions (FA) in host cells. This was shown to enhance cellular attachment of the bacteria to the substratum. For the first time, we show that EspO family of effectors function as anti-apoptotic effectors. Using in-vitro infection of cells, we demonstrate that EspO family of effectors also interact with another host protein called HAX-1. HAX-1 is an anti-apoptotic protein. We found that EspO co-localizes with HAX-1 to mitochondria of infected cells. Interestingly, ectopic expression of the interactor was able to shift the distribution of EspO from FA to mitochondria. By virtue of its association with HAX-1, EspO was able to protect cells from apoptosis triggered by multiple inducers including staurosporine (a global kinase inhibitor), tunicamycin (induces unfolded protein response) and thapsigargin (interferes with Ca2+ homeostasis). Additionally, EspO protects the infected cells from apoptosis induced by EPEC infections. These results indicate that despite the differences between EHEC, S. Typhimurium and Shigella, manipulation of HAX-1 anti-apoptotic signaling cascade is a common theme employed by enteric pathogens to maintain the viability of infected cells and sustain its infectious foothold.

Figure 1: Schematic to illustrate association of T3SS effector EspO with host protein HAX-1.

Our finding that EspO has a new interaction partner, HAX-1, opened up an entirely new dimension to its function during infection.

What are the possible consequences of these findings for your research area?

EspO is a conserved family of effectors in enteric pathogens. The fact that both extracellular (EHEC) and invasive (Shigella and Salmonella) pathogens use EspO to hijack HAX-1 signalling module indicates that the HAX-1 signalling pathway plays a key role in host pathogen interplay and this warrants further investigation.

What was the exciting moment (eureka moment) during your research?

It was well established that EspO interacts with integrin linked kinase and localize to focal adhesions in infected cells. Our finding that EspO has a new interaction partner, HAX-1, opened up an entirely new dimension to its function during infection. So definitely this was our eureka moment.

What do you hope to do next?

I hope to translate these findings in mouse model of enteric infection using the mouse pathogen, Citrobacter rodentium. I also aim to understand the functional implications of alteration of HAX-1 signalling in context of physiological, in vivo infection.

Where do you seek scientific inspiration?

I seek inspiration from my late grandmother Santi Chatterjee. Sharing an anecdote: When I was in school (standard 1), there was a mistake in a textbook which said that Brahmo Samaj was founded by Swami Vivekananda instead of Raja Ram Mohan Roy. My grandmother spoke to the school teacher and Principal about this error; however, she was told that textbook cannot be wrong. She then wrote a letter to the publisher to point out the mistake. The publisher realised this and promptly sent her and the school principal a letter and the rectified copy of the textbook. What my young mind learned from this incidence is that whatever is written in textbooks can change and challenging the dogma can be rewarding.

How do you intend to help Indian science improve?

India is doing great in terms of novel scientific discoveries. However, I think that there is lack of communication about scientific discoveries to common people, particularly in local languages. Recently I spoke about the science behind Covid vaccines in Hindi on Jharkhand Vidhan Sabha TV (https://www.youtube.com/watch?v=-3vkrle7-_8) to help overcome vaccine hesitancy. I plan to continue such outreach activities in local languages in future.

Another interesting concept, which I came across in UK, is charity funding for science such as fundraising events for cancer research, heart disease research and so on. I am not at a stage yet to start such initiatives in India, but I believe this has the potential to enhance research funding and enable active participation from the community.

Reference

Chatterjee, S., Lekmeechai, S., Constantinou, N., Grzybowska, E.A., Kozik, Z., Choudhary, J.S., Berger, C.N., Frankel, G. and Clements, A. (2021), The type III secretion system effector EspO of enterohaemorrhagic Escherichia coli inhibits apoptosis through an interaction with HAX-1. Cellular Microbiology. e13366. https://doi.org/10.1111/cmi.13366

Prof. Frankel’s lab at Imperial College, London: https://www.imperial.ac.uk/people/g.frankel

Prof. Tatu’s lab at Indian Institute of Science, Bangalore: https://biochem.iisc.ac.in/utpal-s-tatu.php

Edited by: Anjali Mahilkar

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