Cellular and molecular consequences of defective Fanconi anemia proteins in replication-coupled DNA repair: mechanistic insights.
The Fanconi anemia (FA) molecular network consists of 15 "FANC" proteins, of which 13 are associated with mutations in patients with this cancer-prone chromosome instability disorder. Whereas historically the common phenotype associated with FA mutations is marked sensitivity to DNA interstrand crosslinking agents, the literature supports a more global role for FANC proteins in coping with diverse stresses encountered by replicative polymerases. We have attempted to reconcile and integrate numerous observations into a model in which FANC proteins coordinate the following physiological events during DNA crosslink repair: (a) activating a FANCM-ATR-dependent S-phase checkpoint, (b) mediating enzymatic replication-fork breakage and crosslink unhooking, (c) filling the resulting gap by translesion synthesis (TLS) by error-prone polymerase(s), and (d) restoring the resulting one-ended double-strand break by homologous recombination repair (HRR). The FANC core subcomplex (FANCA, B, C, E, F, G, L, FAAP100) promotes TLS for both crosslink and non-crosslink damage such as spontaneous oxidative base damage, UV-C photoproducts, and alkylated bases. TLS likely helps prevent stalled replication forks from breaking, thereby maintaining chromosome continuity. Diverse DNA damages and replication inhibitors result in monoubiquitination of the FANCD2-FANCI complex by the FANCL ubiquitin ligase activity of the core subcomplex upon its recruitment to chromatin by the FANCM-FAAP24 heterodimeric translocase. We speculate that this translocase activity acts as the primary damage sensor and helps remodel blocked replication forks to facilitate checkpoint activation and repair. Monoubiquitination of FANCD2-FANCI is needed for promoting HRR, in which the FANCD1/BRCA2 and FANCN/PALB2 proteins act at an early step. We conclude that the core subcomplex is required for both TLS and HRR occurring separately for non-crosslink damages and for both events during crosslink repair. The FANCJ/BRIP1/BACH1 helicase functions in association with BRCA1 and may remove structural barriers to replication, such as guanine quadruplex structures, and/or assist in crosslink unhooking.
Thompson
Larry H
LH
Biology and Biotechnology Division, L452, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, United States. thompson14@llnl.gov
Hinz
John M
JM
D000818:Animals; D016466:CHO Cells; D043171:Chromosomal Instability; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004260:DNA Repair; D004261:DNA Replication; D005199:Fanconi Anemia / Q000235:genetics*; D051856:Fanconi Anemia Complementation Group Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008957:Models, Genetic; D009154:Mutation; D018384:Oxidative Stress; D012854:Sister Chromatid Exchange
D051856:Fanconi Anemia Complementation Group Proteins