Fig. 4. The InlB-mediated signaling pathways. In bacteria present in the environment, InlB is buried into the bacterial cell wall, somehow protected from proteolytic degradation and external aggressive agents. Upon infection, in proximity with the targeted host cell, it may dissociate from the bacterial surface, by interacting with GAGs and gC1q-R and become accessible to the Met receptor. (1) The surface-exposed protein will trigger entry of the bacteria. (2) A pool of the protein may be released in the medium and induce signals as a prelude to or independently from entry. InlB-Met interactions induce recruitment of adapters proteins, some of which become tyrosine-phosphorylated, and recruitment and activation of the p85-p110 PI 3-kinase. Some downstream events induce actin cytoskeleton rearrangements involving Rho GTPases and cytoskeletal regulatory proteins, and membrane reorganization, leading to bacteria uptake. Other downstream events, involving activation of other enzymes, such as PLC or Akt, might affect the bacterial fate into the cell and/or the host cell behavior. Hashed arrows indicate hypothetical steps.