PROTEIN TRANSLOCATION INTO HOST EPITHELIAL-CELLS BY INFECTING ENTEROPATHOGENIC ESCHERICHIA-COLI

Enteropathogenic Escherichia coli (EPEC) causes diarrhoea in young chi ldren. EPEC induces the formation of actin pedestal in infected epithe lial cells. A type III protein secretion system and several proteins t hat are secreted by this system, including EspB, are involved in induc ing the formation of the actin pedestals. We have demonstrated that co ntact of EPEC with HeLa cells is associated with the induction of prod uction and secretion of EspB. Shortly after infection, EPEC initiates translocation of EspB, and EspB fused to the CyaA reporter protein (Es pB-CyaA), into the host cell. The translocated EspB was distributed be tween the membrane and the cytoplasm of the host cell. Translocation w as strongly promoted by attachment of EPEC to the host cell, and both attachment factors of EPEC, intimin and the bundle-forming pill, were needed for full translocation efficiency. Translocation and secretion of EspB and EspB-CyaA were abolished in mutants deficient in component s of the type III protein secretion system, including sepA and sepB mu tants. EspB-CyaA was secreted but not translocated by an espB mutant. These results indicate that EspB is both translocated and required for protein translocation by EPEC.