The ability of activation-induced cytidine deaminase (AID) to efficiently mediate class-switch recombination (CSR) is dependent on its phosphorylation at Ser38; however, the trigger that induces AID phosphorylation and the mechanism by which phosphorylated AID drives CSR have not been elucidated. Here we found that phosphorylation of AID at Ser38 was induced by DNA breaks. Conversely, in the absence of AID phosphorylation, DNA breaks were not efficiently generated at switch (S) regions in the immunoglobulin heavy-chain locus (Igh), consistent with a failure of AID to interact with the endonuclease APE1. Additionally, deficiency in the DNA-damage sensor ATM impaired the phosphorylation of AID at Ser38 and the interaction of AID with APE1. Our results identify a positive feedback loop for the amplification of DNA breaks at S regions through the phosphorylation- and ATM-dependent interaction of AID with APE1.

IMPORTANCETraditionally, liver transplant (LT) for alcohol-associated liver disease (ALD) requires 6 months of abstinence. Although early LT before 6 months of abstinence has been associated with decreased mortality for decompensated ALD, this practice remains controversial and concentrated at a few centers. OBJECTIVE To define patient, allograft, and relapse-free survival in early LT for ALD, and to investigate the association between these survival outcomes and early vs standard LT. DESIGN, SETTING, AND PARTICIPANTSThis cohort study analyzed all patients with ALD who underwent their first LT at a single academic referral center between October 1, 2012, and November 13, 2020. Patients with known pretransplant hepatocellular carcinoma, hepatitis B or C, or an alternative cause of liver failure were excluded. Follow-up period was defined as the time from LT to the most recent encounter with a transplant center or death.EXPOSURES The exposure of interest was early LT, which was defined as less than 180 days of pre-LT abstinence. Standard LT was defined as 180 days or more of pre-LT abstinence. Patients were separated into early LT and standard LT by time from abstinence to LT. MAIN OUTCOMES AND MEASURESThe outcomes were patient, allograft, relapse-free, and hazardous relapse-free survival for patients who underwent early LT or standard LT. These groups were compared by log-rank testing of Kaplan-Meier estimates. Hazardous relapse was defined as binge, at-risk, or frequent drinking. Abstinence was reassessed at the most recent follow-up visit for all patients. RESULTSOf the 163 patients with ALD included in this study, 88 (54%) underwent early LT and 75 (46%) underwent standard LT. This cohort had a mean (SD) age at transplant of 52 (10) years and was predominantly composed of 108 male patients (66%). Recipients of early LT vs standard LT were younger (median [interquartile range (IQR)] age, 49.7 [39.0-54.2] years vs 54.6 [48.7-60.0] years; P < .001) and had a higher median (IQR) Model for End-stage Liver Disease score at listing (35.

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