Fig. 3. Role of cofilin during InlB-induced phagocytosis. Adapted from (Bierne et al., 2001). (1) Interaction of InlB with its receptors induces recruitment of the Arp2/3 complex (not shown) and of cofilin (represented by grey circles), which stimulate actin polymerization (represented by lines). LIM-kinase and the phosphatase SSH could be recruited to the phagocytic cup to regulate cofilin's activity. In a first step, LIM-kinase prevents excessive depolymerization of actin filaments by partly inactivating cofilin. Then, SSH would reactivate cofilin, which finally accumulates on the filaments and favors the disruption of the actin network during the retraction of the phagocytic cup and around the newly formed phagosome. Cofilin would thus be involved in both assembly and disassembly of the InlB-induced phagocytic cup. (2) Increasing the pool of active cofilin by expressing the constitutively active S3A cofilin or by inhibiting endogenous LIM-kinase blocks phagocytic cup formation, presumably because of an excess of depolymerizing activity. (3) Partial inactivation of cofilin by overexpressing LIMK1 induces an intense and disorganized accumulation of actin filaments at the phagocytic cup, preventing the engulfment of the particle into the cell.