Spatiotemporal Regulation of a Legionella pneumophila T4SS Substrate by the Metaeffector SidJ

Abstract

Modulation of host cell function is vital for intracellular pathogens to survive and replicate within host cells. Most commonly, these pathogens utilize specialized secretion systems to inject substrates (also called effector proteins) that function as toxins within host cells. Since it would be detrimental for an intracellular pathogen to immediately kill its host cell, it is essential that secreted toxins be inactivated or degraded after they have served their purpose. The pathogen Legionella pneumophila represents an ideal system to study interactions between toxins as it survives within host cells for approximately a day and its Dot/Icm type IVB secretion system (T4SS) injects a vast number of toxins. Previously we reported that the Dot/Icm substrates SidE, SdeA, SdeB, and SdeC (known as the SidE family of effectors) are secreted into host cells, where they localize to the cytoplasmic face of the Legionella containing vacuole (LCV) in the early stages of infection. SidJ, another effector that is unrelated to the SidE family, is also encoded in the sdeC-sdeA locus. Interestingly, while over-expression of SidE family proteins in a wild type Legionella strain has no effect, we found that their over-expression in a ∆sidJ mutant completely inhibits intracellular growth of the strain. In addition, we found expression of SidE proteins is toxic in both yeast and mammalian HEK293 cells, but this toxicity can be suppressed by co-expression of SidJ, suggesting that SidJ may modulate the function of SidE family proteins. Finally, we were able to demonstrate both in vivo and in vitro that SidJ acts on SidE proteins to mediate their disappearance from the LCV, thereby preventing lethal intoxication of host cells. Based on these findings, we propose that SidJ acts as a metaeffector to control the activity of other Legionella effectors.

Toxicity and SidJ-Mediated Suppression of Toxicity Require Distinct Regions in the SidE Family of Legionella pneumophila Effectors

“…This suggests that SdeA and SidJ are both toxic to yeast when produced at high levels. This observed toxicity and suppression are consistent with recently published data showing a similar relationship between SdeA and SidJ (29).…”

“…Thus, the SidE and SidJ proteins are predicted to work in concert to regulate host processes during infection by L. pneumophila. These data are consistent with a recent study that showed a functional interaction between SdeA and SidJ in yeast and on the LCV (29). In addition, we show here that SdeA contains distinct toxicity and SidJ suppression regions.…”

“…All other candidates failed to show suppression when directly challenged with the toxic effector. The genes sidJ and sdeA are carried together on a 20-kb stretch of DNA on the L. pneumophila chromosome that also carried two other SidE family members: sdeB and sdeC (29,39). The previously identified examples of effectors capable of suppressing the toxicity of other effectors have revealed genetic linkage, which provides further support for the hypothesis that SidJ may regulate the toxic activity displayed by SdeA.…”

Right on Q: Genetics begin to Unravel Coxiella Burnetii host cell Interactions

“…However, the complex effector pool of Coxiella undoubtedly modulates additional eukaryotic systems for pathogen benefit such as the cytoskeleton [146], ubiquitination [147] and nuclear processes via the activity of an emerging class of effectors known as nucleomodulins [148,149]. Elucidating signal transduction events that trigger effector translocation, the temporal reliance on effector groups during infection and whether effector-effector regulation occurs [150,151], are of much interest to the field.…”

Creating a customized intracellular niche: subversion of host cell signaling byLegionellatype IV secretion system effectors

“…The underlying molecular mechanisms are poorly defined. SidJ was recently shown to be a metaeffector regulating the LCV localization of the effector SidE and its paralogues, which suggests that its impact on ER recruitment might be indirect (Jeong et al 2015a). Notably, LegK2 possesses autokinase and protein kinase activity in vitro, and this activity is needed to fulfil its role in LCV maturation; however, a host cell target has not yet been identified (Hervet et al 2011).…”