CD44 binds to the Shigella IpaB protein and participates in bacterial invasion of epithelial cells

Shigella entry into epithelial cells is characterized by a transient reorga nization of the host cell cytoskeleton at the site of bacterial interaction with the cell membrane, which leads to bacterial engulfment in a macropino cytic process. Using affinity chromatography on HeLa cell extracts, we show here that the hyaluronan receptor CD44 associates with IpaB, a Shigella pr otein that is secreted upon cell contact. Overlay and solid-phase assays in dicated that IpaB binds directly to the extracellular domain of CD44; bindi ng is saturable and inhibitable, with a half- maximal inhibitory concentrat ion of 175 nM. Immunoprecipitation experiments showed that IpaB associates with CD44 during Shigella entry. CD44 is recruited at bacterial entry sites and localizes at the plasma membrane of cellular extensions induced by Shi gella. Pretreatment of cells with an anti-CD44 monoclonal antibody resulted in inhibition of Shigella-induced cytoskeletal reorganization, as well as inhibition of bacterial entry, whereas transfection of CD44 in cells that a re deficient for CD44 results in increased bacterial binding to cells and i nternalization. The IpaB-CD44 interaction appears to be required for Shigel la invasion by initiating the early steps of the entry process.