Cell-Based Screen Identifies Human Interferon-Stimulated Regulators of Listeria monocytogenes Infection

Abstract

The type I interferon (IFN) activated transcriptional response is a critical antiviral defense mechanism, yet its role in bacterial pathogenesis remains less well characterized. Using an intracellular pathogen Listeria monocytogenes (Lm) as a model bacterial pathogen, we sought to identify the roles of individual interferon-stimulated genes (ISGs) in context of bacterial infection. Previously, IFN has been implicated in both restricting and promoting Lm growth and immune stimulatory functions in vivo. Here we adapted a gain-of-function flow cytometry based approach to screen a library of more than 350 human ISGs for inhibitors and enhancers of Lm infection. We identify 6 genes, including UNC93B1, MYD88, AQP9, and TRIM14 that potently inhibit Lm infection. These inhibitors act through both transcription-mediated (MYD88) and non-transcriptional mechanisms (TRIM14). Further, we identify and characterize the human high affinity immunoglobulin receptor FcγRIa as an enhancer of Lm internalization. Our results reveal that FcγRIa promotes Lm uptake in the absence of known host Lm internalization receptors (E-cadherin and c-Met) as well as bacterial surface internalins (InlA and InlB). Additionally, FcγRIa-mediated uptake occurs independently of Lm opsonization or canonical FcγRIa signaling. Finally, we established the contribution of FcγRIa to Lm infection in phagocytic cells, thus potentially linking the IFN response to a novel bacterial uptake pathway. Together, these studies provide an experimental and conceptual basis for deciphering the role of IFN in bacterial defense and virulence at single-gene resolution.

Type I IFNs in the female reproductive tract: The first line of defense in an ever-changing battleground

“…Several ISGs have been identified as having antibacterial effects, including MYD88 and TRIM1. 36 Furthermore, IFNs can induce a more systemic defense by activating NK and CD8+ T cell cytotoxicity as well as by increasing antigen presentation and recruitment of the adaptive immune system.…”

Actin assembly-inducing protein ActA promotes FcγRIa-mediatedListeriainternalization

“…Our previous studies demonstrated that FcγRIa did not promote cellular uptake of intracellular bacteria S. flexneri or S. Typhimurium. Additionally, FcγRIa did not confer an invasive phenotype to L. innocua, a non-pathogenic Listeria species closely related to Lm (8). These findings suggest that a bacterial Fcγ receptor ligand is specific to pathogenic Listeria and potentially provides an advantage in survival and dissemination during infection.…”

“…Strikingly, we previously found that Lm is internalized by FcγRIa-expressing cells independently of antibody interaction or ITAM-mediated signaling, hallmarks of IgG-opsonized particles uptake. Additionally, this process did not involve wellcharacterized host Lm internalization receptors (E-cadherin and c-Met) or bacterial surface internalins (InlA and InlB) (8). Thus, FcγRIa-mediated Lm entry occurs through a non-canonical mechanism.…”

“…We previously established that ectopic expression of FCGR1A in HEK293A cells was sufficient to reconstitute FcγRIa-mediated Lm internalization independently of E-cadherin and c-Met expression, as well as immunoglobulin opsonization of bacteria (8). Here, we employed this simplified system to investigate the molecular interplay involved in Lm cellular invasion through FcγRIa.…”

“…Recently, we reported that interferon-inducible receptor FcγRIa promotes Lm invasion of human monocytic cells (8). FcγRIa (also known as CD64) is a high-affinity immunoglobulin G receptor (IgG) receptor, expressed on the surface of monocytes, macrophages, and activated neutrophils (9).…”