FANCD2 regulates BLM complex functions independently of FANCI to promote replication fork recovery

Abstract

Fanconi Anemia (FA) and Bloom Syndrome share overlapping phenotypes including spontaneous chromosomal abnormalities and increased cancer predisposition. The FA protein pathway comprises an upstream core complex that mediates recruitment of two central players, FANCD2 and FANCI, to sites of stalled replication forks. Successful fork recovery depends on the Bloom’s helicase BLM that participates in a larger protein complex (‘BLMcx’) containing topoisomerase III alpha, RMI1, RMI2 and replication protein A. We show that FANCD2 is an essential regulator of BLMcx functions: it maintains BLM protein stability and is crucial for complete BLMcx assembly; moreover, it recruits BLMcx to replicating chromatin during normal S-phase and mediates phosphorylation of BLMcx members in response to DNA damage. During replication stress, FANCD2 and BLM cooperate to promote restart of stalled replication forks while suppressing firing of new replication origins. In contrast, FANCI is dispensable for FANCD2-dependent BLMcx regulation, demonstrating functional separation of FANCD2 from FANCI.

The USP1-UAF1 complex interacts with RAD51AP1 to promote homologous recombination repair

“…32,33 FANCD2-Ub also interacts with the TLS polymerase eta. 34 Unmodified FANCD2 is also required for chromatin loading of Blm, 35 and functionally interacts with FANCJ [36][37][38] and PCNA. 39 Among these functions of FANCD2, the recruitment of CtIP to the DSB ends would have significant effects on the HR repair, as the CtIP-induced DSB end resection is the initiating event of the HR repair process.…”

The Fanconi anemia ID2 complex: Dueling saxes at the crossroads

“…130 Furthermore, neither FANCI nor FANCD2 monoubiquitination are required to promote BLM complex chromatin assembly, indicating that this function is monoubiquitination and FANCI-independent. 130 Nucleosome Assembly Activity FANCD2 was recently identified in a proteomics screen of histone H3/H4-interacting proteins. 135 Recombinant FANCD2 was subsequently confirmed to bind to H3/H4 in vitro.…”

“…For example, it has recently been determined that FANCD2, and not FANCI, is an important regulator of the recruitment of the BLM helicase to chromatin. 130 Biallelic mutations in the BLM gene underlie Bloom syndrome (BS), a rare recessive disorder characterized by growth retardation, sunlight sensitivity, telangiectasia, hypo-or hyper-pigmentation of the skin, and increased susceptibility to hematologic cancers. 131 The BLM helicase is a member of the RecQ family of helicases, which also includes the WRN and RECQ4 proteins, and possesses ATP-dependent 3 0 -5 0 DNA helicase activity.…”

Rad51 recombinase prevents Mre11 nuclease-dependent degradation and excessive PrimPol-mediated elongation of nascent DNA after UV irradiation

“…Over the past few years, it has become evident that Rad51 escorts ongoing replication forks regardless of the presence of DSBs (3)(4)(5). Specifically, Rad51 protects persistently stalled replication forks from Mre11-mediated nucleolytic degradation and facilitates replication fork restart when the replication-halting agent hydroxyurea (HU) or aphidicolin (APH) is removed (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Such novel functions of Rad51 require many HRR factors, including BCRA2, FANCD2 (Fanconi Anemia Complementation group protein D2), CtIP, BRCA1, and the WRN helicase, but are independent of HRR effectors, such as Rad54 (6,7).…”