The BRCA1-associated FANCJ helicase is among those helicases able to unwind G4 DNA in vitro, and FANCJ mutations are associated with breast cancer and linked to Fanconi anemia.
Using targeted capture and massively parallel genomic sequencing, 151 subjects with USC were assessed for germline mutations in 30 tumor suppressor genes, including BRCA1 (breast cancer 1, early onset), BRCA2, the DNA mismatch repair genes (MLH1 [mutL homolog 1], MSH2 [mutS homolog 2], MSH6, PMS2 [postmeiotic segregation increased 2]), TP53 (tumor protein p53), and 10 other genes in the Fanconi anemia-BRCA pathway.
BACH1 (BRCA1-associated C-terminal helicase 1), the product of the BRIP1 {BRCA1 [breast cancer 1, early onset]-interacting protein C-terminal helicase 1; also known as FANCJ [FA-J (Fanconi anaemia group J) protein]} gene mutated in Fanconi anaemia patients from complementation group J, has been implicated in DNA repair and damage signalling.
Genes mutated in patients with Fanconi anemia (FA) interact with the DNA repair genes BRCA1 and BRCA2/FANCD1 to suppress tumorigenesis, but the molecular functions ascribed to them cannot fully explain all of their cellular roles.
Crosslinking agents and ionizing radiation induce damage in cancer cells that requires the FA/BRCA pathway to be resolved; thus cancers that are deficient in BRCA1, BRCA2, or any other component of the FA/BRCA pathway are hypersensitive to these agents.
The link between BRCA1 dysfunction and basal-like breast cancer or triple-negative breast cancer (TNBC) has been suggested; however, the associations of other factors involved in the Fanconi anemia (FA)/BRCA pathway with the pathogenesis of basal-like breast cancer remain unidentified.
One of the more recently identified FA proteins, shown to be responsible for complementation of the FA complementation group J, is the BRCA1 Associated C-terminal Helicase (BACH1, designated FANCJ), originally identified as a protein associated with breast cancer.
Epigenetic silencing of essential components of DNA repair pathways is a common event in many tumor types, and comprise O6-methylguanine-DNA methyltransferase (MGMT), human mut L homolog 1 (hMLH1), Werner syndrome gene (WRN), breast cancer susceptibility gene 1 (BRCA1), and genes of the Fanconi anemia pathway.
Inactivating and truncating mutations of the nuclear BRCA1-interacting protein 1 (BRIP1) have been shown to be the major cause of Fanconi anaemia and, due to subsequent alterations of BRCA1 function, predispose to breast cancer (BC).
The BRCA1 associated C-terminal helicase (BACH1, designated FANCJ) is implicated in the chromosomal instability genetic disorder Fanconi anemia (FA) and hereditary breast cancer.
We showed that BRCA1 mediates the recruitment of FANCD2 by gammaH2AX to damaged chromatin and cells deficient or depleted of H2AX exhibit an FA-like phenotype, including an excess of chromatid-type chromosomal aberrations and hypersensitivity to MMC.
Several components of the Fanconi anaemia (FA) family of proteins allow the formation of the DNA repair complex foci formed by proteins such as BRCA1/2 and RAD51.
Therefore, the ATR- and BRCA1-mediated FA pathway is required for the activation of a G2/M checkpoint and for DNA damage repair in response to the endogenous signal of rereplication.
The proteins involved in FA act coordinately in the cellular response to DNA cross-links in a pathway that has been shown to interact physically or functionally with a variety of other proteins involved in DNA repair or cell cycle control, notably BRCA1, Rad51,ATM,ATR, and Nbs1.
Because brip1 mutant cells are proficient for ubiquitination of FANCD2 protein, our data indicate that BRIP1 has a function in the Fanconi anemia pathway that is independent of BRCA1 and downstream of FANCD2 activation.
Fanconi anemia (FA) and cells lacking functional BRCA1 and BRCA2 proteins are hypersensitive to interstrand crosslinking (ICL) agents and show increased numbers of chromosomal breaks and radials.
Using chromosomal stability after ICL damage as the end point, we find that BRCA1 functions in more than just the FA pathway for genome maintenance, whereas BRCA2 appears to act predominantly in the FA pathway.
Other diseases combining the phenotype of chromosomal instabilities and neoplastic development are Fanconi anemia and breast cancers associated with mutant BRCA1 and BRCA2 genes.
A previously reported molecular interaction between BRCA1 and the FA protein, FANCD2, supports the hypothesis that both breast-cancer-susceptibility genes are components of the FA pathway, functioning in DNA-damage response.
FANCD2, a downstream component of the FA pathway, has recently been shown to be ubiquitinated in response to DNA damage and to translocate to nuclear foci containing BRCA1, a breast cancer susceptibility gene product, suggesting a role for this protein in DNA repair functions.