HDAC6 Regulates Antibody-dependent Intracellular Virus Neutralization By Deacetylating TRIM21

Viruses are parasites that cannot survive without their host cells.Antibodies are important for immune system of the body to defend against invading viruses.Due to the shielding effect of cell membranes,antibodies were initially thought to only play a role in neutralizing viruses outside the cell.However,the discovery of the cytoplasmic IgG receptor,Tripartite motif-containing protein 21(TRIM21),has changed the traditional perception of how antibodies neutralize virus infection.TRIM21 is a member of the TRIM protein family and consists of multiple domains.The N-terminus is a RING domain with E3 ubiquitin ligase activity,the middle region contains a B-BOX domain and two coiled-coil domains,and the C-terminus is a unique PRYSPRY domain.As an antibody receptor,TRIM21 can bind to the virus-antibody complex and mediates its transport to the proteasome for degradation.This process is called antibody-dependent intracellular virus neutralization.In this process,TRIM21 homodimerization is required for its interaction with antibodys,and TRIM21 ubiquitination is required for its targeting to the proteasome.However,the exact mechanism that regulates TRIM21 activity is unknown.Our previous study revealed an interaction between TRIM21 and histone deacetylase 6(HDAC6).In this study,we found that TRIM21 was a substrate of HDAC6 and that the function of TRIM21 was regulated by HDAC6-mediated deacetylation.Through adenovirus infection experiments,we found that inhibition of HDAC6 expression affected antibody-dependent intracellular virus neutralization.Immunofluorescence experiments showed that HDAC6 was colocalized with TRIM21 in the cytoplasm,and co-immunoprecipitation experiments showed that HDAC6 interacted with TRIM21.Inhibition of HDAC6 activity impaired TRIM21 dimerization.By constructing different TRIM21 truncation plasmids based on its multiple domains,we found that TRIM21 interacted with HDAC6 through itsPRYSPRY domain.Acetylation of proteins occurs predominantly at lysine residues.There are a total of seven lysine residues in the PRYSPRY domain of TRIM21.We constructed point mutation plasmids for these lysine residues.Through immunoprecipitation and adenovirus infection experiments,we found that the deacetylation of two lysine residues in TRIM21 might mediate its role in antibody-dependent intracellular virus neutralization.Taken together,our study reveals that HDAC6 deacetylates TRIM21 at specific lysine residues.Excessive acetylation of TRIM21 inhibits its dimerization,which prevents its binding to the virus-antibody complex and targeting to proteasome-mediated degradation.Our study of the deacetylation-mediated regulation of TRIM21 activity provides novel insights into the antibody-dependent intracellular virus neutralization.