Ubiquitination of PCNA and Its Essential Role in Eukaryotic Translesion Synthesis

Abstract

Ubiquitin and ubiquitin-like proteins (Ubls) are now at the center stage of molecular and cell biology because of their diverse functions in many fundamentally important cellular processes. Besides the celebrated role of ubiquitin in the 26S proteasome-mediated protein degradation pathway, the non-proteolytic functions of ubiquitin are being uncovered at a fast pace. The prominent examples include membrane trafficking, innate immunity, kinase signaling, chromatin dynamics and DNA damage response. Researchers in the area of DNA damage response have witnessed rapid progress within the past decade, largely stimulated by the seminal findings that ubiquitination and SUMOylation of a key DNA replication/repair protein, proliferating cell nuclear antigen (PCNA), controls precisely how eukaryotic cells respond to different types of DNA damage, and how cellular DNA damage repair or tolerance pathways are selected to cope with damage in the DNA genome. Here, we will review the recent findings on translesion synthesis (TLS) and its regulation by PCNA ubiquitination in eukaryotes. We will discuss two prevalent models, i.e., the postreplicative gap-filling and the polymerase switch, which have been invoked to account for eukaryotic cells' ability to overcome DNA damage associated replication blockade through TLS. Results from both in vitro reconstitution and from genetic systems will be discussed. We will also summarize the recent findings revealing the crosstalk between two major human DNA damage response pathways (the TLS and the Fanconi anemia pathways), and the ATR and ATM-independent regulation of PCNA ubiquitination. Lastly, new methods of preparing ubiquitinated PCNA will be reviewed. The availability of milligram levels of ubiquitinated PCNA will help our understanding of the molecular details in eukaryotic TLS.

Deregulated origin licensing leads to chromosomal breaks by rereplication of a gapped DNA template

“…These data suggest that Emi1 depletion progressively induces ssDNA accumulation, which goes undetected by the DDR and precedes rereplication-associated DNA breaks. Importantly, PCNA ubiquitylation, a sensitive marker of replication-associated ssDNA gaps (for review, see Chen et al 2011), was detectable within 24 h (Fig. 2C) and thus earlier than other DDR markers (Fig.…”

Regulation and Modulation of Human DNA Polymerase δ Activity and Function

“…The stalled replicative polymerase (usually taken as Pol δ) is switched for a translesion polymerase that bypasses the lesion. The most studied example of translesion synthesis is that performed by Pol η in the bypass of UV-induced CPDs (cyclobutane pyrimidine dimers) [85][86][87][88][89]. The key event that is required for initiation of translesion synthesis is the mono-ubiquitination of PCNA [90], following which Pol δ is switched for Pol η [91,92].…”

A Novel Function of CRL4Cdt2

“…In addition to its roles in DNA replication, Pol ␦ also acts as the gap-filling enzyme in DNA repair processes. Evidence for this has been found in nucleotide excision repair (NER) (14,15), heteroduplex extension during homologous recombination, double strand break repair (16,17), and in translesion synthesis during the switch with translesion polymerases (18) in the DNA damage tolerance pathway (19,20). There is also evidence that Pol ␦ participates in long patch base excision repair (21).…”

“…RNF8 plays a central role in the DNA damage response during the assembly of the complexes that orchestrate the activation of homologous recombination, checkpoints, and apoptotic signaling in response to ionizing radiation damage (27)(28)(29). In addition, RNF8 efficiently mono-ubiquitinates PCNA both in vitro and in vivo (30), a process central to the activation of translesion synthesis by Pol and other translesion synthesis polymerases (19,31).…”