There's a lot more in the manuscript, check it out! So many wonderful people worked on this through years but led by Daniel Bennison (postdoc). Thanks also to our fantastic collaborators at Imperial, The Crick, IISc Bangalore, U Geneva and MIVEGEC!

Caspase-4 is also recruited to these structures in a GBP1-dependent manner, independently of LPS!

GBP1 is recruited to sites of 'sterile' actin-rich structures produced by FcgR-Tir chimera independently of LPS!

We made an FcgR-Tir chimera, i.e., Fcg-Receptor extracellular domain + intracellular signalling domain of Tir, and activated it by crosslinking with IgG-coated polystyrene beads. This produces 'sterile' actin-rich structures independently of bacteria, other T3SS-effectors & LPS!

GBP1 directly binds LPS and recruits caspase-4 on cytosolic Gram-negative bacteria. We showed LPS is internalised during EPEC infection (pubmed.ncbi.nlm.nih.gov/33378358/). But, does GBP1 recruitment need LPS or actin polymerisation? To address this, we reconstituted Tir-actin signalling.

How does GBP1 sense these extracellular bacteria? Using a range of EPEC and EHEC mutants, we show that pathogen-induce actin polymerisation is essential for GBP1 recruitment, pyroptosis and IL-18 release (a substrate of human caspase-4).

Guess what, GBP1 recruits caspase-4 to EPEC/EHEC pedestals for pyroptosis. This clarifies the role of caspase-4 that we previously showed in pyroptosis caused by these pathogens. (pubmed.ncbi.nlm.nih.gov/31018119/; pubmed.ncbi.nlm.nih.gov/33378358/).

GBP1 is also recruited to actin pedestals of EHEC in epithelial cells and C. rodentium-infected colonocytes in vivo in mice.

We show that GBP1 is recruited to actin-rich pedestals of EPEC. The T3SS mutant strain (escF) cannot manipulate actin, recruit GBP1 or trigger pyroptosis. Importantly, GBP1 is recruited to pedestals of various EPEC strains independently of the type of their LPS O-antigens.

EPEC/EHEC and the mouse pathogen C. rodentium (CR) attach tightly to cells and manipuate the host actin cytosokeleton by forming actin-rich 'pedestals'. This requires the T3SS-effector Tir (translocated intimin receptor) binding to Intimin (an adhesin on bacterial surface).

We've worked on extracellular Gram-negative pathogenic E. coli (EPEC & EHEC) for several years. EPEC is a major cause of childhood diarrhoeas and EHEC can be fatal even in adults. Here we show that GBP1 is required for EPEC/EHEC-induced pyroptosis in non-phagocytic cells.

Details of the scholarship scheme here:
nosmsje.gov.in/nosmsje/