The role of the ubiquitin ligase Cul4b in B lymphocytes

Abstract

Abstract Vaccination or infection induces antibody secretion by long-lived plasma cells, creating durable immune protection against secondary infections. These plasma cells develop from B cells that have undergone affinity maturation, which requires somatic hypermutation in proliferating B cells, forming single strand DNA breaks that are repaired by mismatch repair machinery. Cullin 4b (Cul4b) is an E3 ubiquitin ligase found in most cells, including B cells, but its function in B cells is unknown. Cul4b is one of two docking proteins forming the backbone of the Cullin RING Ligase 4 (CRL4) complex, which ubiquitinates substrate proteins for degradation. Previous studies have shown that Cul4b promotes DNA repair with cell proliferation, and high Cul4b is linked to aggressive colon cancer. Because proliferation and DNA repair are essential for humoral immunity, we hypothesized that Cul4b also functions in B cells. To test this, we generated mice that lack Cul4b in B cells. We immunized these mice with an mRNA vaccine against an H1N1 Influenza A virus, and measured virus-specific serum antibody. We found that Influenza-specific antibodies were dramatically reduced in mice serum that lacked Cul4b in B cells. To determine if Cul4b promotes DNA damage repair in B cells, we induced single-strand DNA breaks with UV irradiation and then stimulated the cells to proliferate in vitro. We found that Cul4b promoted B lymphocyte proliferation after UV exposure. Understanding the Cul4b-DNA damage repair pathway in B cells will identify new drug targets to transiently amplify this pathway to improve vaccines and encourage stronger antibody responses, or to inhibit this pathway to prevent tumor progression in cancer.