FANCJ Helicase Defective in Fanconia Anemia and Breast Cancer Unwinds G-Quadruplex DNA to Defend Genomic Stability

Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA; National Institute of Advanced Industrial Science and Technology, Tokyo 135-0064, Japan

^* To whom correspondence should be addressed. Email: BroshR{at}grc.nia.nih.gov.

	Abstract

FANCJ mutations are associated with breast cancer and genetically linked to the bone marrow disease Fanconi Anemia (FA). Genomic instability of FA-J mutant cells suggests FANCJ helicase functions in the replicational stress response. Putative helicases with sequence similarity to FANCJ in C. elegans (DOG-1) and mouse (RTEL) are required for polyG-tract maintenance, suggesting their involvement in resolution of alternate DNA structures that impede replication. Under physiological conditions, guanine-rich sequences spontaneously assemble into four-stranded structures (G4) that influence genomic stability. FANCJ unwound G4 DNA substrates in an ATPase-dependent manner. FANCJ G4 unwinding is specific since another Superfamily 2 helicase, RECQ1, failed to unwind all G4 substrates tested under conditions the helicase unwound duplex DNA. RPA stimulated FANCJ G4 unwinding, whereas the mismatch repair complex MSH2/6 inhibited this activity. FANCJ-depleted cells treated with the G4 interactive compound telomestatin displayed impaired proliferation, elevated apoptosis and DNA damage compared to siRNA control cells, suggesting that G4 DNA represents a physiological substrate of FANCJ. Although the FA pathway has been classically described in terms of interstrand cross-link (ICL) repair, the cellular defects associated with FANCJ mutation extend beyond the reduced ability to repair ICLs and involve other types of DNA structural roadblocks to replication.