UC Davis

The intracellular pathogen Brucella abortus establishes a replicative niche within cells of the reticuloendothelial system primarily via expression of its main virulence factor; the type 4 secretion system (T4SS) and its effectors. Unlike many other pathogens, whose secretion system and effectors tend to be co-localized in the genome and co-regulated by the same transcriptional regulators, the genes encoding T4SS effectors in Brucella spp. are scattered throughout its genome and have regulation that is poorly described. Therefore, the mechanisms that facilitate coordinated spaciotemporal expression of effectors with the type 4 secretion system remain a mystery. Our research has revealed that, in the case of the effector protein VceB, Brucella abortus utilizes a post-transcriptional mechanism to direct the translation of transcript that is already present and does not induce nor does it require further transcription of VceB. Nutrient limitation in the form of amino acid starvation, a primary environmental signal sensed by Brucella, was found to be sufficient to drive induction of VceB translation. Amino acid starvation is known to elicit a global stress response called the stringent response which is implicated by these findings. Preliminary data, suggest that this phenomenon could be widely employed by Brucella abortus to regulate several other of its known effectors and is the first instance where post transcriptional regulation has been implicated in effector regulation in Brucella spp. A second study was conducted as part of this dissertation and focused on investigating the function of the VceB effector. Previously, the effector VceB was revealed to localize to the ER compartment and elicit TNFα production. Our initial hypothesis was that VceB mediated inflammation was linked to the ER stress sensor IRE1α and the unfolded protein response (UPR) like a known effector; VceC. Here we present evidence that ectopic expression of VceB does not induce UPR transcripts or protein production. Furthermore, infections of an IRE1α knock out cell line resulted in no significant differences in TNFα production. While inconclusive, these data suggest VceB mediated inflammation is not reliant on IRE1α or induction of the UPR.