Formin‐mediated actin polymerization promotes S almonella invasion

Summary S almonella invade host cells using T ype 3 secreted effectors, which modulate host cellular targets to promote actin rearrangements at the cell surface that drive bacterial uptake. The Arp 2/3 complex contributes to S almonella invasion but is not essential, indicating other actin regulatory factors are involved. Here, we show a novel role for FHOD 1, a formin family member, in S almonella invasion. FHOD 1 and Arp 2/3 occupy distinct microdomains at the invasion site and control distinct aspects of membrane protrusion formation. FHOD 1 is phosphorylated during infection and this modification is required for promoting bacterial uptake by host cells. ROCK II , but not ROCK I , is recruited to the invasion site and is required for FHOD 1 phosphorylation and for S almonella invasion. Together, our studies revealan important phospho‐dependent FHOD 1 actin polymerization pathway in S almonella invasion.