Final Report Summary - MODELIST (Understanding the infection by the bacterium Listeria monocytogenes as a way to address key issues in biology)
This project intended to study unexplored facets of the infection by the food-borne bacterial pathogen Listeria monocytogenes, taken as a model system, to discover new concepts in infection biology, in cell biology and in microbiology. Major achievements have been obtained and published in high impact journals(Cell, Science, Nature …) and one patent has been deposited.
New RNA-mediated regulations in bacteria;
We have analyzed in details how the bacterium adapts its transcriptional programme when it switches from the environment where it is ubiquitously present, to the intestine and then the blood of orally-infected animals and discovered two major global switches and identified the regulators that are involved. We have discovered a series of unpredicted novel types of regulations and an unanticipated complexity in bacterial gene expression. In particular, we have identified dual functions RNAs in regions that we called excludons. We have discovered that the short transcript generated by riboswitches can as as a non coding regulatory element,. We have identified vitamin B12 riboswitch regulated non-coding RNAS that play key role in metabolism either acting as riboswitch regulated antisense or as riboswitch regulated protein sequestering RNA. Together, these findings provide several new frameworks for the generation of novel therapeutics.
Unexplored facets of the cell biology of infections and new concepts in cell biology;
The study of host pathogens interactions in vitro, i.e. by infecting cells in culture, may help discovering how bacteria subvert host functions and how cells counteract infection, generating new concepts to fight against infections. This type of studies also allows to better understand cellular components or mechanisms which are otherwise difficult to address.
Septins : we discovered that an infected cell can entrap invading bacteria in cages made of septin filaments and prevent their dissemination to neighboring cells. Septins were up to recently uncharacterized components of the cytoskeleton. Our discovery highlights a new strategy used by the organisms to counteract infections and provide a physiological role for complex filaments which had so far been mainly considered as scaffolding components or key players in diffusion barriers. Increasing the « caging » by TNF impairs infection, paving the way to new strategies to fight infections.
Post-translational modifications: we have shown that during infection Listeria prevents the SUMOylation of host proteins by inducing the degradation of Ubc 9, the enzyme involved in this post translational modification and that this event is necessary for an efficient infection, revealing a new mechanism used by pathogens to subvert host functions and reinforcing the view that pathogens may target a variety of post -translational modifications. We have now set up a mass spectrometry based approach to identify SUMO targets modified upon a signal such as an infection.
Mitichondrial dynamics: we have observed that mitochondria - key cellular organelles involved in energy production - are fragmented early during infection, and that this fragmentation impairs their function, i.e. ATP production. This fragmentation is transient, representing an unexpected strategy used by pathogens to impair the cell physiology and allow establishment of the infection. Strikingly this fragmentation appears atypical and not to use factors used during classical fragmentation.
Chromatin remodeling: The discovery of a Listeria secreted factor LntA able to go to the nucleus of the infected cell, to interact with BAHD1 a protein involved in heterochromatin formation and stimulate a type III interferon response has shown that bacteria can reprogram the transcription of the host cell during infection, revealing that bacteria have evolved tools which may have long lasting epigenetic consequences. Bacteria are also able to modify histones and one key player is SIRT2 which is translocated to the nucleus and represses genes during infection.
Characterization of new virulence bacterial factors;
New virulence factors have been discovered. In addition to LntA, three proteins protect the bacteria from the innate immune response: InlC, a secreted protein which interacts with Ikk- and inhibits the NF-kB pathway in response to infection. OatA, an enzyme which modifies the peptidoglycan allowing escape from the innate immune response. InlK : a surface protein which recruits a ribonucleoprotein which protects bacteria from the autophagy machinery.
The intestinal phase of infection (coll with M Lecuit);
We have described in more details how bacteria cross the intestinal barrier and shown that at first transcytosis takes place We then demonstrated a clear role of lactobacilli in protecting mice from Listeria.
New RNA-mediated regulations in bacteria;
We have analyzed in details how the bacterium adapts its transcriptional programme when it switches from the environment where it is ubiquitously present, to the intestine and then the blood of orally-infected animals and discovered two major global switches and identified the regulators that are involved. We have discovered a series of unpredicted novel types of regulations and an unanticipated complexity in bacterial gene expression. In particular, we have identified dual functions RNAs in regions that we called excludons. We have discovered that the short transcript generated by riboswitches can as as a non coding regulatory element,. We have identified vitamin B12 riboswitch regulated non-coding RNAS that play key role in metabolism either acting as riboswitch regulated antisense or as riboswitch regulated protein sequestering RNA. Together, these findings provide several new frameworks for the generation of novel therapeutics.
Unexplored facets of the cell biology of infections and new concepts in cell biology;
The study of host pathogens interactions in vitro, i.e. by infecting cells in culture, may help discovering how bacteria subvert host functions and how cells counteract infection, generating new concepts to fight against infections. This type of studies also allows to better understand cellular components or mechanisms which are otherwise difficult to address.
Septins : we discovered that an infected cell can entrap invading bacteria in cages made of septin filaments and prevent their dissemination to neighboring cells. Septins were up to recently uncharacterized components of the cytoskeleton. Our discovery highlights a new strategy used by the organisms to counteract infections and provide a physiological role for complex filaments which had so far been mainly considered as scaffolding components or key players in diffusion barriers. Increasing the « caging » by TNF impairs infection, paving the way to new strategies to fight infections.
Post-translational modifications: we have shown that during infection Listeria prevents the SUMOylation of host proteins by inducing the degradation of Ubc 9, the enzyme involved in this post translational modification and that this event is necessary for an efficient infection, revealing a new mechanism used by pathogens to subvert host functions and reinforcing the view that pathogens may target a variety of post -translational modifications. We have now set up a mass spectrometry based approach to identify SUMO targets modified upon a signal such as an infection.
Mitichondrial dynamics: we have observed that mitochondria - key cellular organelles involved in energy production - are fragmented early during infection, and that this fragmentation impairs their function, i.e. ATP production. This fragmentation is transient, representing an unexpected strategy used by pathogens to impair the cell physiology and allow establishment of the infection. Strikingly this fragmentation appears atypical and not to use factors used during classical fragmentation.
Chromatin remodeling: The discovery of a Listeria secreted factor LntA able to go to the nucleus of the infected cell, to interact with BAHD1 a protein involved in heterochromatin formation and stimulate a type III interferon response has shown that bacteria can reprogram the transcription of the host cell during infection, revealing that bacteria have evolved tools which may have long lasting epigenetic consequences. Bacteria are also able to modify histones and one key player is SIRT2 which is translocated to the nucleus and represses genes during infection.
Characterization of new virulence bacterial factors;
New virulence factors have been discovered. In addition to LntA, three proteins protect the bacteria from the innate immune response: InlC, a secreted protein which interacts with Ikk- and inhibits the NF-kB pathway in response to infection. OatA, an enzyme which modifies the peptidoglycan allowing escape from the innate immune response. InlK : a surface protein which recruits a ribonucleoprotein which protects bacteria from the autophagy machinery.
The intestinal phase of infection (coll with M Lecuit);
We have described in more details how bacteria cross the intestinal barrier and shown that at first transcytosis takes place We then demonstrated a clear role of lactobacilli in protecting mice from Listeria.