A novel family of type VI-secreted toxins affecting Rho GTPases, actin dynamics and inflammation

点击翻译按钮获取中文摘要

To be successful, pathogens must overcome humoral and cellular innate immune barriers. Host innate immune cells (e.g. macrophages) engulf and trap bacteria in membrane-bound vesicles known as phagosomes. Engulfed pathogens, however, disarm macrophages and counteract immunity by deploying proteins (effectors) that subvert key cellular pathways. The host cell cytoskeleton's critical role in both detection of bacterial pathogens and mobilization of antibacterial responses is an emerging theme in infection biology. Indeed, pathogen-induced disorganization of the actin network is a remarkable anti-host strategy, also perceived by macrophages as a danger signal driving inflammation and cell death. However, the actin network in the context of chronic diseases that impair macrophage functions (e.g. cystic fibrosis, diabetes, chronic obstructive pulmonary disease) has not been explored. We and others discovered that cystic fibrosis (CF) gene-defective macrophages fail to clear engulfed bacteria and play a central role in maintaining the chronic inflammation state associated with disease. Based on the CF model, we hypothesize that intracellular pathogens engulfed by macrophages, combined with an underlying chronic defect, induce disorganization of the actin network that leads to a highly proinflammatory state.We will examine this hypothesis using the intracellular opportunistic pathogen Burkholderia cenocepacia, which infects 2-10% of CF patients worldwide, rapidly accelerating their clinical decay. Unlike other CF pathogens, Burkholderia cenocepacia does not reside in biofilms in the lungs of patients but primarily within macrophages. We established Burkholderia cenocepacia as a model organism for cellular microbiology. Specifically, a Burkholderia cenocepacia type VI-secretion system (T6SS-Bc) disrupts the actin network and elicits pyroptosis in macrophages (cell death with exaggerated proinflammatory responses). These phenotypes depend on TecA ("T6SS effector protein affecting cytoskeletal Architecture"), a novel toxin recently discovered in our laboratory that inactivates Rho GTPases. This landmark discovery underpins the proposed study combining cellular and molecular microbiology approaches to investigate how intracellular Burkholderia cenocepacia manipulates the macrophages' actin network. We will address 3 questions:(i)How TecA is secreted by the T6SS-Bc?(ii)How defective actin polymerization is sensed by the Pyrin inflammasome?(iii) What is the status of the Pyrin inflammasome in Burkholderia cenocepacia infected CF gene-defective human peripheral monocytes?Understanding how opportunistic pathogens modulate the macrophages' actin network to drive inflammation will enable the discovery of new checkpoints for controlling dysregulated inflammation secondary to bacterial infection, which could be targeted to develop novel therapies to treat patients with chronic, underlying immune disorders.