Wnt signaling during Ehrlichia infection

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Ehrlichia chaffeensis is a gram-negative obligately intracellular bacterium and the etiologic agent of human monocytotropic ehrlichiosis (HME), an emerging life-threatening tick-borne zoonosis. E. chaffeensis utilizes a class of type 1 secreted (T1S) exoproteins, the tandem repeat protein (TRP) effectors, to facilitate internalization and promote intracellular survival. TRP genes are highly expressed during infection of mammalian hosts, and are involved in diverse interactions with host target proteins including components of Wnt signaling pathways. Wnt signaling, typically studied in the context of development, oncogenic growth, and inflammation, is known to influence cell proliferation, differentiation, phagocytosis, and autophagy. Ehrlichia TRP32 and TRP120 interact with host transcription cofactors and components of feedback pathways that regulate Wnt signaling. We have determined that E. chaffeensis upregulates Wnt-mediated gene transcription, and inhibition or knockdown of components of canonical and non canonical Wnt pathways prevents E. chaffeensis entry and survival. The long-term goal of this research project is to understand the role of the Wnt pathway in E. chaffeensis infection and intracellular survival. The objective of this proposal is to determine the mechanisms through which Ehrlichia induce Wnt pathway activation and the functional implications related to bacterial internalization and intracellular survival. We hypothesize that E. chaffeensis activates the Wnt canonical and non canonical pathways via T1S TRP effector-host interactions to induce phagocytosis, intracellular survival through suppressing autophagy. In aim 1, we will characterize E. chaffeensis activation of Wnt pathways, and the functional implications for bacterial infection and survival. Aim 2 will identify the pathogen-host interactions involved in E. chaffeensis-induced Wnt activation, and the role of the ehrlichial TRP effectors in modulating Wnt signaling. Targeting of Wnt signaling by Ehrlichia for the purpose of entry and survival provides an excellent model in which to investigate microbial molecular and cellular manipulation of these pathways. Our study will provide insight into cellular/molecular network-altering strategies utilized by these intracellular pathogens to gain access to host cells and avoid killing mechanisms. Understanding the significance of the interaction between E. chaffeensis TRPs and host Wnt pathways will contribute to our broader knowledge of bacterial effectors, the context in which these effectors function, and further define their molecular functional roles as moonlighting effectors. We expect that knowledge gained through this investigation will also contribute to the identification of new molecular targets for development of alternative antimicrobial therapeutics.