DNA damage tolerance in stem cells, ageing, mutagenesis, disease and cancer therapy

Abstract

The DNA damage response network guards the stability of the genome from a plethora of exogenous and endogenous insults. An essential feature of the DNA damage response network is its capacity to tolerate DNA damage and structural impediments during DNA synthesis. This capacity, referred to as DNA damage tolerance (DDT), contributes to replication fork progression and stability in the presence of blocking structures or DNA lesions. Defective DDT can lead to a prolonged fork arrest and eventually cumulate in a fork collapse that involves the formation of DNA double strand breaks. Four principal modes of DDT have been distinguished: translesion synthesis, fork reversal, template switching and repriming. All DDT modes warrant continuation of replication through bypassing the fork stalling impediment or repriming downstream of the impediment in combination with filling of the single-stranded DNA gaps. In this way, DDT prevents secondary DNA damage and critically contributes to genome stability and cellular fitness. DDT plays a key role in mutagenesis, stem cell maintenance, ageing and the prevention of cancer. This review provides an overview of the role of DDT in these aspects.

Figure 1.

Modes of DNA damage tolerance. Upon stalling of the replication fork, several modes of DDT can be activated. TLS and fork reversal can occur at the stalled fork. Alternatively, TLS or template switching can occur after repriming event. Figure adapted from (23).

Figure 2.

Translesion synthesis. TLS pathways are regulated by PCNA K164 ubiquitination or REV1. PCNA Ub can also interact with REV1 directly, as with other TLS polymerases. PAF15 is degraded upon fork stalling, which allows PCNA to interact with TLS polymerases. RPA recruits RAD6/RAD18 ligase that can ubiquitinate PCNA to recruit TLS polymerases. SPRTN binds PCNA Ub preventing PCNA deubiquitylation. After TLS is completed, the TLS polymerase replaced again by the replicative polymerase. In the REV1-dependent pathway, REV1 can recruit other TLS polymerases. Figure adapted from (23).

Figure 3.

Homology-directed DNA damage tolerance. Homology-directed DDT involves template switching and fork reversal. In order to prevent use of the fork stalling entity as template, the nascent DNA of the sister chromatid is used. Template switching occurs after a priming event in a post replicative gap. After fork stalling, the replication fork can reverse. Fork reversal leads to a chicken foot intermediate structure, which allows access to the nascent DNA of the sister chromatid.

Figure 4.

Regulation of PRIMPOL by RPA. (A) PRIMPOL is inhibited from access to single-stranded DNA by high concentration of RPA on DNA. (B) When the amount of RPA coating single-stranded DNA is low, PRIMPOL can bind single-stranded DNA and form a primer for a replicative polymerase to continue.

Figure 5.

Translesion synthesis during interstrand crosslink repair. Interstrand crosslinks can be induced by cisplatin, mitomycin C, psoralen and abasic sites. Cisplatin and mitomycin C are repaired by the Fanconi anemia pathway (A), whereas psoralen and abasic site induced ICL are repaired through NEIL3-dependent pathway (B andC). Figure adapted from (23).