In summary our studies provide insight

In summary, our studies provide insight into how a GSK-3 Inhibitor IX australia modification, namely Dot1-dependent H3K79 methylation, regulates the tolerance to alkylating damage by TLS through modulation of Rad53 activity. TLS constitutes one important aspect of the coordinated global cellular response to DNA damage because of the ability to bypass lesions that impede replication progression, thus preventing fork collapse and eventual formation of DNA breaks potentially leading to chromosomal rearrangements. However, given the error-prone nature of TLS, this process must be kept under strict control to avoid excessive mutagenesis, which can also have deleterious consequences. Therefore, an appropriate balance between error-prone and error-free processes to face DNA damage is essential to avoid genomic instability, which is directly linked to cancer development. Our studies in yeast reveal that the conserved Rad53 checkpoint kinase contributes to finely tune this balance at least by regulating the levels of chromatin-bound Rev1. Recent studies using a mouse model point to the influence of correct Rev1 levels in reducing the incidence of carcinogen-induced lung cancer [73], highlighting the importance of these mechanisms for the maintenance of genomic stability.
Conflict of interest
Acknowledgements We thank M. Foiani, T. Hishida, R. Rothstein, M.A. Osley and G.C. Walker for providing plasmids and/or strains. We are indebted to F. van Leeuwen for sharing reagents and results prior to publication. We are especially grateful to R. Freire for raising the anti-Dot1 antibody and to F. Prado and J.A. Tercero for comments on the manuscript. DO and AGS were supported by predoctoral fellowships from CSIC and MEC (Spain), respectively. Research in our labs is supported by grants from Ministry of Science and Innovation of Spain (BFU2009-06938 to AB and BFU2009-07159 to PSS) and a grant from Fundación Ramón Areces to PSS.
Introduction Coping with DNA damage is possible thanks to surveillance mechanisms (checkpoints), that detect the problem and promote its solution [1], [2], and to repair and tolerance pathways that remove the lesions or reduce the damage consequences [3], [4]. Failures in these processes have a high cost, as they are frequently linked to genome instability, a predominant characteristic of cancer cells [5], [6], [7]. Genome stability is especially at risk during chromosomal replication. DNA replication errors affect cell survival and are aggravated and many times originated by DNA damage. DNA synthesis can be compromised when replication forks encounter DNA lesions. Forks are then vulnerable and need to be stabilized, and lesions have to be repaired to complete DNA replication successfully [8], [9], [10], [11], [12], [13]. In budding yeast, the S phase checkpoint, mediated by the conserved kinases Mec1 and Rad53 (human ATR and Chk2, respectively), stabilizes replication forks in response to DNA damage or replicative stress [14], [15]. It also protects forks at fragile sites [16], [17], regulates origin firing [18], [19], [20] and allows fork restart [21]. Moreover, the checkpoint helps to regulate the choice of the repair pathway [22]. The stabilization of stalled forks is the crucial downstream effector of the checkpoint in maintaining cell viability [23]. It is thought to occur, at least in conditions of dNTP depletion, by preserving the replisome at replication forks [24], [25], [26], [27] and through restraining recombination activities at forks [28], [29]. Fork stabilization prevents the accumulation of gapped, hemireplicated and four-branched molecules [30], [31], [32]. All these responses need previous checkpoint activation, which in turn requires the establishment of DNA replication forks [23].