Browsing by Author "Smith, Jeffrey"
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Item Open Access Pathogen evasion of chemokine response through suppression of CXCL10(2019-02-22) Antonia, Alejandro; Alvarez, Monica; Trahair, Esme; Gibbs, Kyle; Pittman, Kelly; Barnes, Alyson; Smith, Jeffrey; Smith, Jeffrey; Rajagopal, Sudarshan; Thompson, Will; Reinhardt, Lee; Ko, DennisAbstract Clearance of intracellular pathogens, such as Leishmania ( L. ) major , depends on an immune response with well-regulated cytokine signaling. Here we describe a pathogen-mediated mechanism of evading CXCL10, a chemokine with diverse antimicrobial functions, including T cell recruitment. Infection with L. major in a human monocyte cell line induced robust CXCL10 transcription without increasing extracellular CXCL10 protein concentrations. We found that this transcriptionally independent suppression of CXCL10 is mediated by the virulence factor and protease, glycoprotein-63 ( gp63) . Specifically, GP63 cleaves CXCL10 after amino acid A81 at the base of a C-terminal alpha-helix. Cytokine cleavage by GP63 demonstrated specificity, as GP63 cleaved CXCL10 and its homologues, which all bind the CXCR3 receptor, but not distantly related chemokines, such as CXCL8 and CCL22. Further characterization demonstrated that CXCL10 cleavage activity by GP63 was produced by both extracellular promastigotes and intracellular amastigotes. Crucially, CXCL10 cleavage impaired T cell chemotaxis in vitro , indicating that cleaved CXCL10 cannot signal through CXCR3. Ultimately, we propose CXCL10 suppression is a convergent mechanism of immune evasion, as Salmonella enterica and Chlamydia trachomatis also suppress CXCL10. This commonality suggests that counteracting CXCL10 suppression may provide a generalizable therapeutic strategy against intracellular pathogens. Importance Leishmaniasis, an infectious disease that annually affects over one million people, is caused by intracellular parasites that have evolved to evade the host’s attempts to eliminate the parasite. Cutaneous leishmaniasis results in disfiguring skin lesions if the host immune system does not appropriately respond to infection. A family of molecules called chemokines coordinate recruitment of the immune cells required to eliminate infection. Here, we demonstrate a novel mechanism that Leishmania (L.) major employs to suppress host chemokines: an L. major protease cleaves chemokines known to recruit T cells that fight off infection. We observe that other common human intracellular pathogens, including Chlamydia trachomatis and Salmonella enterica , reduce levels of the same chemokines, suggesting a strong selective pressure to avoid this component of the immune response. Our study provides new insights into how intracellular pathogens interact with the host immune response to enhance pathogen survival.Item Open Access Physiological Functions of Biased Signaling at the Chemokine Receptor CXCR3(2019) Smith, JeffreyG protein-coupled receptors (GPCRs) are the largest class of receptors in the human genome and one of the most common drug targets. It is now well-established that GPCRs can signal through multiple transducers, including heterotrimeric G proteins, G protein receptor kinases, and beta-arrestins. Certain ligands can preferentially activate certain signaling cascades while inhibiting others, a phenomenon referred to as biased signaling. While biased signaling is observed in many ex-vivo assays, the physiological relevance of biased signaling is not well established. Using the chemokine receptor CXCR3, a receptor that regulates T cell function, and its endogenous chemokines CXCL9, CXCL10, and CXCL11, I established that endogenous biased signaling exists at CXCR3. After identifying small molecule biased CXCR3 agonists using cell-based assays, I utilized human samples and mouse models of T cell movement and inflammation to determine that differential activation of either the G protein or beta-arrestin signaling pathways downstream of CXCR3 produces distinct functional differences. I identified that beta-arrestin regulated-Akt signaling appears critical for full efficacy chemotaxis. I conclude that biased signaling at CXCR3 produces distinct physiological responses.