HP1 regulates the localization of FANCJ at sites of DNA double‐strand breaks

Abstract

The breast and ovarian cancer predisposition protein BRCA1 forms three mutually exclusive complexes with Fanconi anemia group J protein (FANCJ, also called BACH1 or BRIP1), CtIP, and Abraxas/RAP80 through its BRCA1 C terminus (BRCT) domains, while its RING domain binds to BRCA1‐associated RING domain 1 (BARD1). We recently found that the interaction between heterochromatin protein 1 (HP1) and BARD1 is required for the accumulation of BRCA1 and CtIP at sites of DNA double‐strand breaks. Here, we investigated the importance of HP1 and BARD1–HP1 interaction in the localization of FANCJ together with the other BRCA1–BRCT binding proteins to clarify the separate role of the HP1‐mediated pathway from the RNF8/RNF168‐induced ubiquitin‐mediated pathway for BRCA1 function. FANCJ interacts with HP1γ in a BARD1‐dependent manner, and this interaction was enhanced by ionizing radiation or irinotecan hydrochloride treatment. Simultaneous depletion of all three HP1 isoforms with shRNAs disrupts the accumulation of FANCJ and CtIP, but not RAP80, at double‐strand break sites. Replacement of endogenous BARD1 with a mutant BARD1 that is incapable of binding to HP1 also disrupts the accumulation of FANCJ and CtIP, but not RAP80. In contrast, RNF168 depletion disrupts the accumulation of only RAP80, but not FANCJ or CtIP. Consequently, the accumulation of conjugated ubiquitin was only inhibited by RNF168 depletion, whereas the accumulation of RAD51 and sister chromatid exchange were only inhibited by HP1 depletion or disruption of the BARD1–HP1 interaction. Taken together, the results suggest that the BRCA1–FANCJ and BRCA1–CtIP complexes are not downstream of the RNF8/RNF168/ubiquitin pathway, but are instead regulated by the HP1 pathway that precedes homologous recombination DNA repair.

NBS1 interacts with HP1 to ensure genome integrity

“…These findings suggest that the tandem BRCT domains could contribute, along with the pentapeptide, to the interaction with HP1α. This is reminiscent of what observed in BARD1 in which the conserved HP1α-binding pentapeptide is located within the BRCT domain and allows the interaction with the CSD of HP1α 56,57 . Differently from NBS1 silencing, the interaction of p26- and p70-NBS1 fragments with HP1α results in an accumulation of HP1α through mechanisms that remain unclear.…”

Functional analysis of BARD1 missense variants in homology-directed repair and damage sensitivity

“…The BRCT domain has been shown to interact with the HP1 protein in order to retain both the BRCA1-BARD1 complex and CtIP, which is involved in DNA end resection, at the damage site [26]. The BARD1-HP1 interaction is also necessary for the accumulation of DNA helicase FANCJ at sites of DNA damage [37]. BARD1 L570E/V571E and L570A/V571A variants have been shown to inhibit the interaction between BARD1 and HP1 [26].…”

Effects of Sepantronium Bromide (YM-155) on the Whole Transcriptome of MDA-MB-231 Cells: Highlight on Impaired ATR/ATM Fanconi Anemia DNA Damage Response

“…Not only this, but YM-155 also adversely affects the partner and localizer of BRCA2 (PALB2 [-2.33, p<0.001]), which is required for protein linking BRCA1, BRCA2 and RAD51 at the site of a DNA double-strand break. This is pivotal because a combined reduction of BRCA1 interacting protein C-terminal helicase 1, BRIP1 [-6.37, p=6.43E-07] (FANCJ) at both time points would prevent its role as a major helicase needed to interact with BRCA1 to oversee homologous recombination DNA repair and cell response to replication stresses (64). Although many more targets are centered around YM-155 mediated impairment to the DNA damage response pathway, as a last example, we see reduction in exonuclease 1 (EXO1 [-4.57, p<0.001]) which is required for 5' resection in DNA mismatch repair processes involving homologous recombination repair at stalled replication forks (65)(66)(67).…”