Evidence for subcomplexes in the Fanconi anemia pathway

Abstract

Fanconi anemia (FA) is a genomic instability disorder, clinically characterized by congenital abnormalities, progressive bone marrow failure, and predisposition to malignancy. Cells derived from patients with FA display a marked sensitivity to DNA cross-linking agents, such as mitomycin C (MMC). This observation has led to the hypothesis that the proteins defective in FA are involved in the sensing or repair of interstrand cross-link lesions of the DNA. A nuclear complex consisting of a majority of the FA proteins plays a crucial role in this process and is required for the monoubiquitination of a downstream target, FANCD2. Two new FA genes, FANCB and FANCL, have recently been identified, and their discovery has allowed a more detailed study into the molecular architecture of the FA pathway. We demonstrate a direct interaction between FANCB and FANCL and that a complex of these proteins binds FANCA. The interaction between FANCA and FANCL is dependent on FANCB, FANCG, and FANCM, but independent of FANCC, FANCE, and FANCF. These findings provide a framework for the protein interactions that occur "upstream" in the FA pathway and suggest that besides the FA core complex different subcomplexes exist that may have specific functions other than the monoubiquitination of FANCD2. IntroductionMultiple pathways are required by the cell to deal with endogenous and exogenous damage to the DNA and to maintain the genome's integrity. The inactivation of these pathways leads to an unstable genome, which increases the risk of tumorigenesis. Many of the genes involved in DNA repair and genomic stability are mutated in cancer predisposition syndromes such as XPA-G (xeroderma pigmentosum), NBS1 (Nijmegen breakage syndrome), and ATM (ataxia telangiectasia). The function of the gene products that are defective in the Fanconi anemia (FA) pathway, which is speculated to act in DNA repair, remains elusive.FA is clinically characterized by congenital abnormalities, progressive bone marrow failure, and predisposition to malignancy, especially acute myeloid leukemia (AML) and squamous cell carcinoma (SCC). Cells derived from patients with FA are hypersensitive to DNA cross-linking agents, such as mitomycin C (MMC) and diexpoxybutane (DEB), which suggests that the FA pathway may be involved in the sensing and/or repair of interstrand cross-links. Cell fusion experiments have identified 12 different complementation groups, and 11 of their corresponding disease genes have been cloned : FANCA, FANCB, FANCC, FANCD1/ BRCA2, FANCD2, FANCE, FANCF, FANCG, FANCJ/BRIP1, FANCL, Many of the FA proteins interact in a nuclear complex, the assembly of which is required for the monoubiquitination of a downstream target, FANCD2. 15 This protein has been the subject of intense investigation in recent years, and several studies have revealed that the monoubiquitinated isoform of FANCD2 enters discrete nuclear foci where it colocalizes with multiple proteins involved in genomic stability including BRCA1, NBS1, and RAD51. [15][16][17] Furthermore, it has b...

Proteomic analysis unveils a FANCA-modulated neddylation pathway involved in CXCR5 membrane targeting and cell mobility

“…Even though the FANCcore complex is assembled in the nucleus, several of the FANCcore complex proteins can be found in cytoplasmic subcomplexes. For example, FANCA has been isolated in association with FANCG, FANCB and FANCL, and FANCC interacts with a FANCE-FANCF subcomplex (Medhurst et al, 2006). Whether these subcomplexes directly or indirectly regulate independent pathways involved in protein PTM remains to be determined in future studies.…”

Cytoplasmic FANCA-FANCC Complex Interacts and Stabilizes the Cytoplasm-dislocalized Leukemic Nucleophosmin Protein (NPMc)

“…Certain components of the FA core complex also form distinct subcomplexes among themselves or with factors outside the core complex (3,8,9). For example, it has been reported that the members of the eight-component FA core complex form two discrete subcomplexes, one composed of FANCA, FANCB, FANCG, FANCL, and FANCM, and the other consisting of FANCC, FANCE, and FANCF (9). Outside the FA core complex, FANCA, FANCC, and FANCG are found to associate with a variety of cellular factors that primarily function in redox-related processes (30).…”

“…Some of the core complex components also form distinct subcomplexes among themselves or with factors outside the core complex (3,8,9). The function of these FA subcomplexes has yet to be elucidated.…”

FANCD2 Western blot as a diagnostic tool for Brazilian patients with Fanconi anemia

“…An increasing number of FA genes have been identified and their allelic products are interconnected with other DNA damage response proteins involved with genomic stability and tumorigenesis (4,5). www.bjournal.com.br have a comprehensive diagnosis of this disease (20,21).…”

“…A general model has been proposed for the FA pathway based on the response to DNA after exposure of cells to genotoxic stress or following replication arrests (22,23). In brief, eight of the cloned FA genes encode for proteins (FANCA, B, C, E, F, G, L, M), which are part of a large nuclear core complex with multiple subunits and E3 ubiquitin ligase activity (5,24). The activation of this complex induced by DNA replication or by DNA-damage results in monoubiquitination of FANCD2, which moves into areas of damaged chromatin to interact with downstream FA members (FANCD1/BRCA2, FANCJ, FANCN) and other DNA-repair proteins such as BRCA1 and RAD51.…”