Pseudomonas aeruginosa injects NDK into host cells through a type III secretion system

Abstract

Pseudomonas aeruginosa is a Gram-negative opportunistic human pathogen possessing a type III secretion system (T3SS) which injects toxic effector proteins into mammalian host cells. In previous studies, P. aeruginosa strains lacking all of the known type III effectors were shown to cause cytotoxicity upon prolonged infection time. In this study, we report the identification of a new cytotoxin, nucleoside diphosphate kinase (NDK), which is injected into eukaryotic cells in a T3SS-dependent manner. Injection of NDK is inhibited by the presence of previously known effectors of the T3SS, with an effectorless strain injecting the highest amount, suggesting active competition with the known T3SS effectors. NDK is shown to cause a cytotoxic response when expressed in eukaryotic cells, and P. aeruginosa strains harbouring NDK also show a greater toxicity than strains lacking it. Interestingly, the cytotoxic effect of intracellular NDK is independent of its kinase activity. In previous studies, NDK was shown to be secreted into culture supernatants via a type I secretion system and cause cytotoxicity in a kinase-dependent manner. Therefore, the current study highlights an alternative route of NDK secretion as well as two different cytotoxic mechanisms of NDK, depending on the extra-or intra-cellular location of the protein.

Nucleoside-Diphosphate-Kinase of P. gingivalis is Secreted from Epithelial Cells In the Absence of a Leader Sequence Through a Pannexin-1 Interactome

“…In breast and other cancer types, the secretion of NDK from cancer cells has been shown to be critical for increased metastatic activity89. Additionally, the importance of NDK secretion for the establishment of persistent chronic infections by opportunistic pathogens has been well documented151011121314151617. Although NDKs have been shown to be secreted by the bacterial cells of a number of microbial species, the specific pathways of bacterial secretion, as well as their secretion from infected host cells, remain to be determined1.…”

EliA is required for inducing the stearyl alcohol-mediated expression of secretory proteins and production of polyester in Ralstonia sp. NT80

“…Among these six proteins, Hcp forms the extracellular part of the type VI secretion machinery and is released into the culture medium by T6SS (Mougous et al, 2006;Records, 2011;Decoin et al, 2014). Ndk (nucleoside diphosphate kinase) and the flagellum proteins FlgK and FlgE, by contrast, are secreted by the T3SS (Macnab, 2004;Neeld et al, 2014). However, we could not predict the pathway by which the lipoprotein (ORF No.…”

“…Of these two proteins, Hcp has been shown to be an extracellular part of the T6SS (Mougous et al, 2006;Records, 2011;Decoin et al, 2014), which has been reported to be involved in secreting virulence-related proteins either out of or directly into the cells of a eukaryotic host (Schell et al, 2007;Burtnick et al, 2011). Secretory Ndk, by contrast, has been shown to be exported via the T3SS and is known to be involved in the virulence of pathogenic bacteria such as Pseudomonas aeruginosa and Mycobacterium tuberculosis (Chakrabarty, 1998;Neeld et al, 2014). To determine whether expression of these secreted proteins was induced at the transcriptional level by stearyl alcohol, mRNA levels of these proteins were analysed by quantitative RT-PCR.…”

Nucleoside Diphosphate Kinase and Flagellin from Pseudomonas aeruginosa Induce Interleukin 1 Expression via the Akt/NF-κB Signaling Pathways

“…7A). This suggests that Ndk could be the T3SS effector responsible for the activation, since Ndk has been identified as an additional effector translocated into cells via T3SS (16). PAK⌬8 did not activate caspase-1 (Fig.…”