DNA damage tolerance is regulated at least in part at the level of proliferating cell nuclear antigen (PCNA) ubiquitination. Monoubiquitination (PCNA-Ub) at lysine residue 164 (K164) stimulates error-prone translesion synthesis (TLS), Rad5-dependent polyubiquitination (PCNA-Ubn) stimulates error-free template switching (TS). To generate high affinity antibodies by somatic hypermutation (SHM), B cells profit from error-prone TLS polymerases. Consistent with the role of PCNA-Ub in stimulating TLS, hypermutated B cells of PCNAK164Rmutant mice display a defect in generating selective point mutations. Two Rad5 orthologs, HLTF and SHPRH have been identified as alternative E3 ligases generating PCNA-Ubnin mammals. As PCNA-Ub and PCNA-Ubnboth make use of K164, error-free PCNA-Ubn-dependent TS may suppress error-prone PCNA-Ub-dependent TLS. To determine a regulatory role of Shprh and Hltf in SHM, we generated Shprh/Hltf double mutant mice. Interestingly, while the formation of PCNA-Ub and PCNA-Ubnis prohibited in PCNAK164RMEFs, the formation of PCNA-Ubnis not abolished in Shprh/Hltf mutant MEFs. In line with these observations Shprh/Hltf double mutant B cells were not hypersensitive to DNA damage. Furthermore, SHM was normal in Shprh/Hltf mutant B cells. These data suggest the existence of an alternative E3 ligase in the generation of PCNA-Ubn.

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doi.org/10.1016/j.dnarep.2010.12.008, hdl.handle.net/1765/34513
D N A Repair
Erasmus MC: University Medical Center Rotterdam

Krijger, P., Lee, K. Y., Wit, N., van den Berk, P., Wu, X., Roest, H., … Jacobs, H. (2011). HLTF and SHPRH are not essential for PCNA polyubiquitination, survival and somatic hypermutation: Existence of an alternative E3 ligase. D N A Repair, 10(4), 438–444. doi:10.1016/j.dnarep.2010.12.008