The Eukaryotic Host Factor 14-3-3 Inactivates Adenylate Cyclase Toxins of Bordetella bronchiseptica and B. parapertussis, but Not B. pertussis.

, , and share highly homologous virulence factors and commonly cause respiratory infections in mammals; however, their host specificities and disease severities differ, and the reasons for this remain largely unknown. Adenylate cyclase toxin (CyaA) is a homologous virulence factor that is thought to play crucial roles in infections. We herein demonstrate that CyaAs function as virulence factors differently between / and CyaA bound to target cells, and its enzyme domain was translocated into the cytosol similarly to CyaA. The hemolytic activity of CyaA on sheep erythrocytes was also preserved. However, in nucleated target cells, CyaA was phosphorylated at Ser, which constitutes a motif (RSXpSXP [pS is phosphoserine]) recognized by the host factor 14-3-3, resulting in the abrogation of adenylate cyclase activity. Consequently, the cytotoxic effects of CyaA based on its enzyme activity were markedly attenuated. CyaA carries the 14-3-3 motif, indicating that its intracellular enzyme activity is abrogated similarly to CyaA; however, CyaA has Phe instead of Ser, and thus, was not affected by 14-3-3. In addition, CyaA impaired the barrier function of epithelial cells, whereas CyaA did not. Rat infection experiments suggested that functional differences in CyaA are related to differences in pathogenicity between / and , , and are bacterial respiratory pathogens that are genetically close to each other and produce many homologous virulence factors; however, their host specificities and disease severities differ, and the reasons for this remain unknown. Previous studies attempted to explain these differences by the distinct virulence factors produced by each species. In contrast, we indicated functional differences in adenylate cyclase toxin, a homologous virulence factor of The toxins of and presumably were inactivated by the host factor 14-3-3 after phosphorylation in target cells, whereas the toxin was not inactivated because of the lack of the phosphorylation site. This is the first study to show that 14-3-3 inactivates the virulence factors of pathogens. The present results suggest that pathogenic differences in are attributed to the different activities of adenylate cyclase toxins.