The Fanconi Anemia Protein FANCM Is Controlled by FANCD2 and the ATR/ATM Pathways

Abstract

In addition to monoubiquitination by the FA core complex, FANCD2 and FANCI are phosphorylated by the two major cell cycle checkpoint kinases, ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3-related),y in response to DNA damage (2-6). ATM-dependent phosphorylation of FANCD2 occurs following ionizing irradiation and is required for activation of the ionizing irradiation-induced intra-S phase checkpoint (4). ATR-dependent phosphorylation of FANCD2 is triggered by various types of DNA damage, including replication stress, and is required for the interstrand cross-link-induced intra-S phase checkpoint response (2, 3). Moreover, phosphorylation by ATR is required for efficient FANCD2 monoubiquitination in response to DNA damage, suggesting that the FA pathway might participate in ATR-dependent coordination of the S phase of the cell cycle (3, 7).The recent identification of a highly conserved FA core complex member, FANCM (8, 9), indicates a direct role of FA pathway proteins in repair steps at sites of DNA damage. FANCM is a homolog of the archaebacterial Hef protein (helicase-associated endonuclease for fork-structured DNA) and contains two DNA processing domains: a DEAH box helicase domain and an XPF/ERCC4-like endonuclease domain. FANCM has ATP-dependent DNA translocase activity and can dissociate DNA triple helices in vitro (8). Moreover, FANCM binds Holliday junctions and DNA replication fork structures in vitro and promotes ATP-dependent branch point migration, suggesting that FANCM might be involved in DNA processing at stalled replication forks (10,11). In human cells, FANCM localizes to chromatin and is required for chromatin recruitment of other FA core complex proteins (8,12). FANCM is phosphorylated during both the M and S phases and in response to DNA-damaging agents (8,12,13). Interestingly, DNA damage-induced phosphorylation of FANCM is independent of the FA core complex (8), suggesting that FANCM is controlled by other, as yet unknown upstream components of the DNA damage response. Here, we used cell-free Xenopus egg extracts to investigate the role of FANCM during replication and in the DNA damage response. We show that Xenopus FANCM (xFANCM) binds chromatin in a replication-dependent manner and is phosphorylated during unperturbed replication as well as in response to various DNA damage structures. Both chromatin recruitment and phosphorylation of xFANCM are partially controlled by xFANCD2, suggesting feedback signaling from xFANCD2 to the upstream xFA core complex via regulation of xFANCM. In addition, chromatin recruitment during unperturbed replication and activation of xFANCM in response to DNA damage are controlled by the xATR and xATM cell cycle kinases.

ATR–ATRIP Kinase Complex Triggers Activation of the Fanconi Anemia DNA Repair Pathway

“…Cells treated for 24 hours with TAM were exposed to cisplatin for an additional 48 hours and then cell viability was determined with flow cytometry. There has been controversy in the literature about the role of ATR in the activation of the FA pathway (30)(31)(32)(33)(34). Although at the moment it is impossible to exclude an unknown kinase other than ATR or ATM playing a small role, our data collectively indicate that ATR-ATRIP kinase is critical in triggering the FA pathway activation via FANCI phosphorylation.…”

Nuclear GIT2 Is an ATM Substrate and Promotes DNA Repair

“…The subsequent DNA damage response (DDR) cascade transduces signals to downstream targets that initiate cell cycle arrest, DNA repair, or apoptosis. ATM forms just one component of DNA damage repair complexes, and more than 30 ATM substrates that maintain genome stability and reduce the risk of disease have been identified, including NBS1 (10,11), p53 (2, 3), CHK1/CHK2 (12,13), BRCA1 (14), SMC1 (15), BID (16), FANCD2 (17), and H2AX (18). The phosphorylation of these targets has been shown to be critical for their function in DDR cascades.…”

A role for the base excision repair enzyme NEIL3 in replication-dependent repair of interstrand DNA cross-links derived from psoralen and abasic sites

“…Fanconi proteins such as FANCD2 may have critical functions in cross-link repair other than unhooking. For example, FANCD2 can modulate chromatin dynamics [132] and may interact with FANCM in the reversal of stalled replication forks [133]. …”