RESUMEN
A diverse antibody repertoire is essential for humoral immunity. Antibody diversification requires the introduction of deoxyuridine (dU) mutations within immunoglobulin genes to initiate somatic hypermutation (SHM) and class switch recombination (CSR). dUs are normally recognized and excised by the base excision repair (BER) protein uracil-DNA glycosylase 2 (UNG2). However, FAM72A downregulates UNG2 permitting dUs to persist and trigger SHM and CSR. How FAM72A promotes UNG2 degradation is unknown. Here, we show that FAM72A recruits a C-terminal to LisH (CTLH) E3 ligase complex to target UNG2 for proteasomal degradation. Deficiency in CTLH complex components result in elevated UNG2 and reduced SHM and CSR. Cryo-EM structural analysis reveals FAM72A directly binds to MKLN1 within the CTLH complex to recruit and ubiquitinate UNG2. Our study further suggests that FAM72A hijacks the CTLH complex to promote mutagenesis in cancer. These findings show that FAM72A is an E3 ligase substrate adaptor critical for humoral immunity and cancer development.
Asunto(s)
Cambio de Clase de Inmunoglobulina , Ubiquitina-Proteína Ligasas , Humanos , Animales , Cambio de Clase de Inmunoglobulina/genética , Ubiquitina-Proteína Ligasas/metabolismo , Ubiquitina-Proteína Ligasas/genética , Ratones , ADN Glicosilasas/metabolismo , ADN Glicosilasas/genética , Células HEK293 , Ubiquitinación , Hipermutación Somática de Inmunoglobulina/genética , Mutagénesis , Reparación del ADN , Proteolisis , Inmunidad Humoral , Ratones Endogámicos C57BLRESUMEN
Activation-induced cytidine deaminase (AID) catalyses the deamination of deoxycytidines to deoxyuracils within immunoglobulin genes to induce somatic hypermutation and class-switch recombination1,2. AID-generated deoxyuracils are recognized and processed by subverted base-excision and mismatch repair pathways that ensure a mutagenic outcome in B cells3-6. However, why these DNA repair pathways do not accurately repair AID-induced lesions remains unknown. Here, using a genome-wide CRISPR screen, we show that FAM72A is a major determinant for the error-prone processing of deoxyuracils. Fam72a-deficient CH12F3-2 B cells and primary B cells from Fam72a-/- mice exhibit reduced class-switch recombination and somatic hypermutation frequencies at immunoglobulin and Bcl6 genes, and reduced genome-wide deoxyuracils. The somatic hypermutation spectrum in B cells from Fam72a-/- mice is opposite to that observed in mice deficient in uracil DNA glycosylase 2 (UNG2)7, which suggests that UNG2 is hyperactive in FAM72A-deficient cells. Indeed, FAM72A binds to UNG2, resulting in reduced levels of UNG2 protein in the G1 phase of the cell cycle, coinciding with peak AID activity. FAM72A therefore causes U·G mispairs to persist into S phase, leading to error-prone processing by mismatch repair. By disabling the DNA repair pathways that normally efficiently remove deoxyuracils from DNA, FAM72A enables AID to exert its full effects on antibody maturation. This work has implications in cancer, as the overexpression of FAM72A that is observed in many cancers8 could promote mutagenesis.
Asunto(s)
Linfocitos B , ADN Glicosilasas , Reparación de la Incompatibilidad de ADN , Cambio de Clase de Inmunoglobulina , Proteínas de la Membrana , Mutación , Proteínas de Neoplasias , Hipermutación Somática de Inmunoglobulina , Animales , Femenino , Humanos , Ratones , Linfocitos B/metabolismo , Sistemas CRISPR-Cas , ADN Glicosilasas/antagonistas & inhibidores , ADN Glicosilasas/metabolismo , Epistasis Genética , Células HEK293 , Cambio de Clase de Inmunoglobulina/genética , Región de Cambio de la Inmunoglobulina/genética , Proteínas de la Membrana/deficiencia , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Ratones Endogámicos C57BL , Proteína 2 Homóloga a MutS/genética , Proteína 2 Homóloga a MutS/metabolismo , Proteínas de Neoplasias/deficiencia , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Hipermutación Somática de Inmunoglobulina/genéticaRESUMEN
The link between the gut microbiome and responsiveness to immune checkpoint inhibitor (ICI) therapy is now well established. New therapeutic opportunities exploiting this relationship are being developed with the goal of augmenting ICI efficacy. In this review, we summarize the foundational research establishing these interactions and discuss the mechanisms and novel therapeutic options associated with this gut microbiome-ICI connection.