A role for cofilin and LIM kinase in Listeria-induced phagocytosis

The pathogenic bacterium Listeria monocytogenes is able to invade nonphagoc ytic cells, an essential feature for its pathogenicity This induced phagocy tosis process requires tightly regulated steps of actin polymerization and depolymerization. Here, we investigated how interactions of the invasion pr otein InIB with mammalian cells control the cytoskeleton during Listeria in ternalization. By fluorescence microscopy and transfection experiments, we show that the actin-nucleating Arp2/3 complex, the GTPase Rac, LIM kinase ( LIMK), and cofilin are key proteins in InIB-induced phagocytosis. Overexpre ssion of LIMK1, which has been shown to phosphorylate and inactivate cofili n, induces accumulation of F-actin beneath entering particles and inhibits internalization. Conversely, inhibition of LIMK's activity by expressing a dominant negative construct, LIMK1(-), or expression of the constitutively active S3A cofilin mutant induces loss of actin filaments at the phagocytic cup and also inhibits phagocytosis. Interestingly, those constructs simila rly affect other actin-based phenomenons, such as InIB-induced membrane ruf fling or Listeria comet tail formations. Thus, our data provide evidence fo r a control of phagocytosis by both activation and deactivation of cofilin. We propose a model in which cofilin is involved in the formation and disru ption of the phagocytic cup as a result of its local progressive enrichment .