Interferon inducible GBPs restrict Burkholderia thailandensis motility induced cell-cell fusion

Abstract

Innate immunity responds to pathogens by producing alarm signals and activating pathways that make host cells inhospitable for pathogen replication. The intracellular bacterium Burkholderia thailandensis invades the cytosol, hijacks host actin, and induces cell fusion to spread to adjacent cells, forming multinucleated giant cells (MNGCs) which promote bacterial replication. We show that type I interferon (IFN) restricts macrophage MNGC formation during B. thailandensis infection. Guanylate-binding proteins (GBPs) expressed downstream of type I IFN were required to restrict MNGC formation through inhibition of bacterial Arp2/3-dependent actin motility during infection. GTPase activity and the CAAX prenylation domain were required for GBP2 recruitment to B. thailandensis, which restricted bacterial actin polymerization required for MNGC formation. Consistent with the effects in in vitro macrophages, Gbp2(-/-), Gbp5(-/-), Gbp(Chr3)-KO mice were more susceptible to intranasal infection with B. thailandensis than wildtype mice. Our findings reveal that IFN and GBPs play a critical role in restricting cell-cell fusion and bacteria-induced pathology during infection. Author summary The intracellular bacterium Burkholderia thailandensis and its relatives B. pseudomallei and B. mallei each invade host cells and hijack the actin cytoskeleton polymerization machinery to transmit to neighboring cells by cell-cell fusion, a transmission strategy that is unique to this family. The high antibiotic resistance of the Burkholderia family underscores the need to understand how the immune system can control infections. Here, we show that the interferon immune response upregulates a family of immune proteins, the guanylate binding proteins (GBPs), to counter the bacterial intracellular motility and, as a consequence, cell-cell fusion. Infected macrophages extensively fuse when lacking key molecules in this immune pathway, and mice lacking the GBP2 or GBP5 proteins are 100-1000-fold more susceptible to infection than wildtype mice, highlighting the critical role this immune pathway plays in restricting bacterial infection and cell-cell fusion. We also found that mice lacking GBPs were protected if bacteria lacked a critical virulence factor, VgrG5, that is required for cell-cell fusion, highlighting that cell-cell fusion is dependent on both bacteria-mediated cytoskeleton remodeling as well as VgrG5. Together, this study provides insight into an intricate host-pathogen interaction key to the virulence of the Burkholderia family.