Formin FHOD1 regulates the size of EPEC pedestals

Enteropathogenic E. coli (EPEC) is an extracellular pathogen that causes polymerization of actin filaments at the site of bacterial attachment, referred to as actin pedestals. Actin polymerization in the pedestal was believed to be solely regulated via the Nck-WASp-Arp2/3 pathway before formins were recently discovered to be associated with pedestals. Herein, we explored the collaborative role of formins in contributing to EPEC pedestal formation. In particular, we discovered that the formin FHOD1 preferentially localized to the pedestal base and its knockdown drastically reduced pedestal surface area. The pedestal localization of formin FHOD1 was found to be dependent on Tir phosphorylation at Y474, and on FHOD1 phosphorylation at Y99 from host Src family kinases (SFKs). Interestingly, differences in Arp2/3 and FHOD1 dynamics were observed. In large pedestals, Arp3 was nearly absent, but FHOD1 levels were high, suggesting that Arp2/3 and formins were segregated temporally. In line with this observation, as the pedestals grew in size, FHOD1 localization increased, while Arp3 localization decreased along the pedestals. Together, our results suggest that EPEC employs multiple actin nucleators that act at different stages of pedestal formation. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=171 SRC="FIGDIR/small/149344v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1711602org.highwire.dtl.DTLVardef@15c060dorg.highwire.dtl.DTLVardef@914447org.highwire.dtl.DTLVardef@119cf28_HPS_FORMAT_FIGEXP M_FIG C_FIG