The cyclin kinase inhibitor p21 is a negative regulator of Translesion DNA synthesis (TLS)

SABRINA FLORENCIA MANSILLA; GASTÓN SORIA; MARÍA BELÉN VALLERGA; MARTÍN HABIF; MARÍA BELÉN FEDERICO; MARINA A. GONZÁLEZ BESTEIRO; AGOSTINA BERTOLÍN; VANESA GOTTIFREDI

Buenos Aires

Congreso; Ubiquitin & UBLs. At the crossroads from chromatin to protein; 2014

EMBO

DNA damage is very frequent and at least 10.000 lesions accumulate per cell daily even in the absence of exogenous stress. Some of those DNA lesions are inevitably encountered by active replisomes. Since replicative DNA polymerases cannot use damaged DNA as template, replication forks stall at DNA lesions. A number of mechanisms facilitate the cellular response to the stalling of replisomes preventing replication catastrophe and cell death at the expenses of a certain risk of increased mutagenesis. From the different pathways activated by DNA replication stress, the activation of TLS (translesion DNA synthesis) is key for the cellular response to the accumulation of bulky adducts. When replicative DNA polymerases stall at those sites, specialized DNA polymerases with more flexible active sites are recruited to DNA to use those adducts as replication templates. While beneficial at stalling sites, the specialized polymerases acquired the ability to accommodate damaged DNA at the expenses of their fidelity. This suggests that their action should be tightly controlled and limited to situation in which replicative polymerases stall or are unable to replicate a given template. This notion is supported by recent finding indicating that some specialized polymerases are overexpressed in transformed cells. In line with the above conception, negative regulators of TLS should be central in the prevention of oncogenesis and to control the extent of TLS onset after genotoxic challenge. We have found that the proteolysis of the cyclin kinase inhibitor p21 (triggered by different E3 ligases including SCFskp2 and CRL4-cdt2) is required for the proper activation of TLS events when DNA adducts accumulate after UV irradiation. To impair TLS, p21 interacts with the replication auxiliary platform PCNA. In that way, p21 prevents the focal recruitment of specialized polymerases to replication factories and their interaction with PCNA on chromatin. Persistent TLS blockage by p21 impairs the elongation of ongoing replication fork increasing both cell death and genomic instability. We will also present data indicating that endogenous levels of p21 which are considered residual,keep specialized polymerases on hold, avoiding their unnecessary recruitment to undamaged DNA templates and preventing the genomic instability that might arise as a consequence of defects in the finalization of DNA replication.