Selective fragmentation of the trans-Golgi apparatus by Rickettsia rickettsii

Author summary Intracellular pathogens have evolved multiple mechanisms to modify the host cell to promote pathogen evasion of host defense mechanisms and enhance pathogen replication. Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, secretes a protease into the host cytosol to cause a fragmentation of the trans-Golgi network (TGN) with minimal effects on the cis-Golgi. Dispersal of the TGN disrupts trafficking of host cellular proteins to the plasma membrane. This includes inhibition of Major Histocompatibility Complex class I molecules to the cell surface thus providing R. rickettsii with a potential means of evading host immune surveillance. Fragmentation of the Golgi apparatus is observed during a number of physiological processes including mitosis and apoptosis, but also occurs in pathological states such as neurodegenerative diseases and some infectious diseases. Here we show that highly virulent strains of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, induce selective fragmentation of the trans-Golgi network (TGN) soon after infection of host cells by secretion of the effector protein Rickettsial Ankyrin Repeat Protein 2 (RARP2). Remarkably, this fragmentation is pronounced for the trans-Golgi network but the cis-Golgi remains largely intact and appropriately localized. Thus R. rickettsii targets specifically the TGN and not the entire Golgi apparatus. Dispersal of the TGN is mediated by the secreted effector protein RARP2, a recently identified type IV secreted effector that is a member of the clan CD cysteine proteases. Site-directed mutagenesis of a predicted cysteine protease active site in RARP2 prevents TGN disruption. General protein transport to the cell surface is severely impacted in cells infected with virulent strains of R. rickettsii. These findings suggest a novel manipulation of cellular organization by an obligate intracellular bacterium to determine interactions with the host cell.