Human cells need to cope with the stalling of DNA replication to complete replication of the entire genome to minimize genome instability. They respond to “replication stress” by activating the conserved ATR-Claspin-Chk1 replication checkpoint pathway. The stalled replication fork is detected and stabilized by the checkpoint proteins to prevent disintegration of the replication fork, to remove the lesion or problems that are causing fork block, and to facilitate the continuation of fork progression. Claspin, a factor conserved from yeasts to human, plays a crucial role as a mediator that transmits the replication fork arrest signal from the sensor kinase, ataxia telangiectasia and Rad3-related (ATR), to the effector kinase, Checkpoint kinase 1 (Chk1). Claspin interacts with multiple kinases and replication factors and facilitates efficient replication fork progression and initiation during the normal course of DNA replication as well. It interacts with Cdc7 kinase through the acidic patch segment near the C-terminus and this interaction is critical for efficient phosphorylation of Mcm in non-cancer cells and also for checkpoint activation. Phosphorylation of Claspin by Cdc7, recruited to the acidic patch, regulates the conformation of Claspin through affecting the intramolecular interaction between the N- and C-terminal segments of Claspin. Abundance of Claspin is regulated at both mRNA and protein levels (post-transcriptional regulation and protein stability) and affects the extent of replication checkpoint. In this article, we will discuss how the ATR-Claspin-Chk1 regulates normal and stressed DNA replication and provide insight into the therapeutic potential of targeting replication checkpoint for efficient cancer cell death.

Fanconi anemia (FA) is a rare genetic disorder characterized by bone marrow failure, developmental abnormalities and a predisposition to cancer, particularly acute myeloid leukemia. So far, 22 FA genes (FANCA-W) have been identified. Germline inactivation of any one of the 22 currently known FA genes causes FA. Proteins encoded by FA genes are involved in the Fanconi anemia pathway, which repairs DNA interstrand crosslinks (ICLs). The main function of the FA pathway in repairing ICLs has been extensively studied. In addition, several lines of evidence indicate that the FA pathway has crucial roles in genome maintenance upon replication stress, and is involved in common fragile sites, R-loops, and mitotic DNA synthesis. Recently, we found that all the functions of the FA pathway are possibly derived from one unified mechanism, namely that FA proteins play a role in the cleavage-coupled break-induced replication pathway to restart stalled replication forks. In the review, we summarize our current understanding of the functions of the FA pathway, and review our knowledge of the potential endogenous pathogenic factors that contribute to FA.

Telomeres are specialized structures located at the ends of chromosomes that are critical for maintaining genomic integrity. Telomeres are shortened during each cycle of cell division because chromosomes are not able to completely replicate, a phenomenon known as the end-replication problem. Telomere shortening or dysfunction causes genome instability and is implicated in a variety of diseases, including cancer, cardiovascular disease and neurodegenerative disorders. Here, we discuss recent advances in basic and clinical research into telomere regulation and maintenance, and highlight how dysfunctional telomeres influence aging and age-related diseases.

Lysine-specific demethylase 1 (LSD1) with oxidation activity that relies on flavin adenine dinucleotide (FAD) to subsequently produce formaldehyde have been associated with various types of cancers. Here, we report an NMR-based assay for detecting the LSD1 enzyme activity. Our approach can be performed in a reaction buffer without any extraction step, achieve a time-dependent absolute quantification, and be useful for the enzyme inhibitor screening. This precise assay allows us to develop new inhibitors of the LSD1 as anticancer agents.