The Function And Mechanism Study Of Proteasome Activator REGγ In Innate Immunity

The immune system plays a crucial role in host defense and maintaining homeostasis.Firstly,pattern recognition receptors,which expressecd on innate immune cell surface,can recognize and bind pathogen-associated molecule patterns of pathogens when the body is invaded by foreign pathogenic microorganisms,resulting in activation of cellular NF-κB and MAPK signaling pathways,then the expression and release of a series of inflammatory mediators,including some proinflammatory factors,chemokines,antibacterial peptides,reactive oxygen(ROS),active nitrogen(NO),etc.One side,these mediators can kill the invaded pathogenic microorganisms directly.On the other hand,by recruiting more inflammatory cells to infection sites,these mediators can amplify the inflammatory signals and clear the infected foreign pathogens further.However,this activation must be under exquisite control in vivo to prevent uncontrolled immune responses,as both immunesuppression or overactivation of immune responses may result in host immune disorders,such as immunesuppression,septic shock or autoimmune diseases,etc.But how the activity of immune system is regulated restrictly in vivo is remain unclear so far.There are lots of studies of proteasomes about innate immunity,but most scientific researches have been focusing on 19S composed proteasomes recently.The role of 11S proteasome activator in innate immunity were less studied,and previous investigations have demonstrated the role of the IFN-y-inducible REGα/β complex in Ag processing,and mice lacking the 11S family member REGy has slightly lower number of CD8+T cells and has impaired function of clearing pulmonary fungal infection,suggesting that maybe REGy can play a potential role in the immune system.Here we find for the first time that LPS can upregulate the expression of REGy,and the data from CHIP assay indicate that REGy is a dowmstream target gene of NF-κB signaling pathway.By infecting the mice with Listeria monocytogenes and cecal ligation and puncture(CLP)to mimic the model of host abdominal infection induced bacteremia,we studied the role of REGy in host resistance to bacterial infection,and the results indicated that REGy-deficient mice showed heavier bacteria load,lower survival and faster weight loss.Thus,REGy-deficient mice had a defect in host defense against both gram positive and negative pathogens.We studied further and found this defect was contributed by haematopoietic and non-haematopoietic cells by bone marrow transplantation assay.As the recruitment of inflammatory cells plays very important roles in bacterial clearance in innate immune system,we infected REGγ-deficient mice with Listeria monocytogenes by intraperitoneal injection and found that infected REGy-deficient mice had decreased numbers of monocytes and neutrophils in peripheral blood and peritoneal fluid.Furthermore,we cocultured bone marrow-derived macrophages with E.Coli or Listeria monocytogenes in vitro,and the results suggested that the bacterial killing activity of REGγ-deficient macrophages was weaker than wild-type cells.The production of iNOS and release of NO were also lower in REGy-deficient macrophages and neutrophils than wild-type cells after LPS treatment,which led to the weaker killing activity of REGy-deficient phagocytes.In addition,LPS induced activation of MAPK signaling,the degradation rate of IκBα and the translocation of P65 to nuclears had not been affected after REGy deficiency.We studied further and found that the reruitment of transcriptional coactivators p300 and PCAF to target genes promoters was attenuated in neuclear after REGγ deficiency,which led to the less production of bactericidal NO and other downstream target cytokines induced by NF-κB signaling pathway.Mechanismsly,we found that REGy can degradate transcriptional factors in phagocytes,then inhibited the inflammatory responses and cell migration induced by KLF2 regulated NF-κB signaling pathway.Collectively,as a activator of proteasome,REGy can play very important roles in innate immune system.Furthermore,this paper also provides new ideas and views for studying the relationship between proteasome system and innate immune system.