ROLE OF FORMIN FHOD1 IN THE ACTIN PEDESTAL FORMATION

Abstract

Enteropathogenic E. coli (EPEC) is an extracellular pathogen that causes polymerization of actin at the site of bacterial attachment, referred to as ‘actin pedestals’. Actin polymerization in the pedestal is believed to be regulated via the Nck-WASp-Arp2/3 pathway. Recent in vivo studies in mice however demonstrated that the Nck-mediated pathway was dispensable for pedestal formation, suggesting involvement of multiple actin nucleators. In this work, we explored the role of formins in the actin pedestal formation. We discovered that the formin, FHOD1 localized to the pedestal base and its knockdown drastically reduced pedestal surface area. FHOD1 knockdowns also compromised host responses to EPEC. 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 are segregated temporally. In line with this observation, as the pedestals grew in size, FHOD1 localization increased while Arp3 decreased. Together, our results suggest a major role for formin-mediated pathways in the growth of pedestals. We find that formin FHOD1 localization to pedestals is independent of the canonical Tir phosphorylation pathway. We also show that the EPEC infection outcomes, i. e. pedestal formation and MRTF-A translocation differ in different cell types.