Vibrio parahaemolyticus orchestrates a multifaceted host cell infection by induction of autophagy, cell rounding, and then cell lysis

Abstract

The bacterial pathogen Vibrio parahaemolyticus utilizes a type III secretion system to cause death of host cells within hours of infection. We report that cell death is completely independent of apoptosis and occurs by a mechanism in which injection of multiple type III effectors causes induction of autophagy, cell rounding, and the subsequent release of cellular contents. Autophagy is detected by the appearance of lipidated light chain 3 (LC3) and by increases in punctae and vacuole formation. Electron microscopy reveals the production of early autophagic vesicles during infection. Consistent with phosphoinositide 3 (PI3) kinase playing a role in autophagy, treatment of infected cells with a PI3 kinase inhibitor attenuates autophagy in infected cells. Because many effectors are injected during a V. parahaemolyticus infection, it is not surprising that the presence of a sole PI3 kinase inhibitor does not prevent inevitable host-cell death. Our studies reveal an infection paradigm whereby an extracellular pathogen uses its type III secretion system to cause at least three parallel events that eventually result in the proinflammatory death of an infected host cell.host-pathogen ͉ type III secretion ͉ apoptosis ͉ effector ͉ inflammatory

The type III secretion system of Vibrio alginolyticus induces rapid apoptosis, cell rounding and osmotic lysis of fish cells

“…Interestingly, V. alginolyticus induces apoptosis during the process of T3SS-mediated cell death, whereas V. parahaemolyticus does not. In contrast to our findings, the T3SS1-mediated cell death of V. parahaemolyticus preserves the integrity of the host-cell nuclear membrane and does not activate caspase molecules (Burdette et al 2008;Zhou et al, 2009). This difference may be due to the inherent differences in the T3SS effectors of V. alginolyticus and V. parahaemolyticus, as there were some minor differences between the hypothetical regions encoding them ( Supplementary Fig.…”

“…EPC cells infected with wild-type ZJO, DvscC or C-vscC, were stained with Hoechst 33258 (Sigma) at indicated time points post-infection as described by Burdette et al (2008). Cells were left untreated or were treated with 2 mM staurosporine (STS) as controls.…”

“…For example, an early study showed that V. parahaemolyticus uses its T3SS1 to induce cell death in HeLa cells through apoptosis (Ono et al, 2006). Recently, Burdette et al (2008) reported that V. parahaemolyticus T3SS1-mediated cytotoxicity is caspaseindependent and involves the induction of autophagy, followed by cell rounding and lysis. More recent studies also suggested that the bacterium kills host cells primarily via oncosis rather than apoptosis, pyroptosis or autophagy (Zhou et al, 2009).…”

Type III secretion system 1 of Vibrio parahaemolyticus induces oncosis in both epithelial and monocytic cell lines

“…For example, it is possible that the wild-type strain (NY-4) and the other six strains used in the present study caused rapid cell death (within 4 h) by unrecognized effector protein(s) of T3SS1 that are absent in the strain used in previous studies (RIMD2210633; unavailable for the present study) and that this rapid cell death prevented detection of apoptosis in our study. Burdette et al (2008) also reported that host cell death induced by V. parahaemolyticus is independent of apoptosis.T3SSs are needle-like structures expressed on the surface of Gram-negative bacteria and upon contact with eukaryotic cells (Cornelis & Van Gijsegem, 2000;Cornelis, 2002Cornelis, , 2006Hueck, 1998;Mota & Cornelis, 2005). These structures become inserted into the cell membrane to create pores in the membrane surface (Neyt & Cornelis, 1999); these pores assist the translocation of effector proteins from bacteria into host cells (Neyt & Cornelis, 1999).…”

“…Nevertheless, the clinical manifestation of vibriosis is consistent with an inflammatory response, including neutrophil recruitment to the site of intestinal infection (Qadri et al, 2003); this inflammatory response is more consistent with oncosis or pyroptosis than apoptosis or autophagy. Furthermore, Burdette et al (2008) have recently reported that V. parahaemolyticus induces autophagy in cell culture, but blocking this pathway does not block cell death. Thus, it is very likely that alternative pathways are primarily responsible for cell death.…”