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. 2013 May 13;23(5):693-704.
doi: 10.1016/j.ccr.2013.03.025.

Function of BRCA1 in the DNA damage response is mediated by ADP-ribosylation

Mo Li  1 , Xiaochun Yu
Affiliations

Function of BRCA1 in the DNA damage response is mediated by ADP-ribosylation

Mo Li et al. Cancer Cell. .

Abstract

Carriers of BRCA1 germline mutations are predisposed to breast and ovarian cancers. Accumulated evidence shows that BRCA1 is quickly recruited to DNA lesions and plays an important role in the DNA damage response. However, the mechanism by which BRCA1 is recruited to DNA damage sites remains elusive. BRCA1 forms a Ring-domain heterodimer with BARD1, a major partner of BRCA1 that contains tandem BRCA1 C-terminus (BRCT) motifs. Here, we identify the BRCTs of BARD1 as a poly(ADP-ribose) (PAR)-binding module. The binding of the BARD1 BRCTs to PAR targets the BRCA1/BARD1 heterodimer to DNA damage sites. Thus, our study uncovers a PAR-dependent mechanism of rapid recruitment of BRCA1/BARD1 to DNA damage sites.

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Figures

Figure 1
Figure 1. The recruitments of BRCA1 and BARD1 to DNA damage sites
(A) The relocation kinetics of BRCA1 to DNA damage sites. GFP-BRCA1 was expressed in WT or H2AX−/− MEFs. The relocation kinetics was monitored in a time course following laser microirradiation (the same for below). (B) The relocation kinetics of the S1655A or K1702A mutants of BRCA1 to DNA damage sites. GFP-WT BRCA1, S1655A or K1702A mutants were expressed in U2OS cells. (C) The relocation kinetics of the BRCA1 BRCTs to DNA damage sites. The GFP-BRCA1 BRCTs was expressed in WT or H2AX−/− MEFs. (D) The relocation kinetics of the C61G mutant of BRCA1 to DNA damage sites. The GFP-BRCA1 C61G mutant was expressed in WT or H2AX−/− MEFs. (E) The relocation kinetics of BARD1 to DNA damage sites. GFP-BARD1 was expressed in WT or H2AX−/− MEFs. (F) The relocation kinetics of the BARD1 BRCTs and the K619A mutant to DNA damage sites. GFP-WT BARD1 BRCTs or the K619A mutant was expressed in WT or H2AX−/− MEFs. (G) The effect of the BARD1 K619A mutant on the recruitment of BRCA1 to DNA damage sites. U2OS cells stably expressing siRNA-resistant WT BARD1 or the K619A mutant were transfected with BARD1 siRNA to deplete endogenous BARD1. GFP-BRCA1 was expressed in these stable cell lines. GFP fluorescence at the laser line was converted into a numerical value (relative fluorescence intensity) using Axiovision software (version 4.5). Normalized fluorescent curves from 20 cells from three independent experiments were averaged. The error bars represent the standard deviation. Scale bar = 10 µm. See also Figure S1.
Figure 2
Figure 2. The BARD1 BRCTs directly bind PAR
(A) The interaction between GST (negative control), GST-CHFR (positive control), GST-BARD1 BRCTs, GST-BARD1 BRCTs K619A mutant, or GST-BRCA1 BRCTs and PAR was examined by dot blot using anti-PAR antibody. PAR was blotted and shown as the input. (B) The interaction between the recombinant proteins in (A) and biotin-PAR was examined by the reciprocal pull-down assay with anti-GST antibody. Recombinant proteins were blotted and shown as the input. (C) The affinity between GST-BARD1 BRCTs or GST-BRCA1 BRCTs and PAR was measured by ITC. Titration of PAR was injected into a solution containing the purified protein. The inset shows the fit of the data to an equilibrium binding isotherm. The fit provides an equilibrium dissociation constant (KD) for the binding of PAR to the protein. (D) The affinity between GST-BARD1 BRCTs or GST-BARD1 BRCTs K619A mutant and ADP-ribose was measured by ITC (left). Affinities between the BRCA1 BRCTs, BARD1 BRCTs, or BARD1 BRCTs mutants and ADP ribose or PAR are summarized in the table (right). (E) The in vivo interaction between BARD1 or the mutants and PAR was measured by co-IP and reciprocal co-IP. (F) The in vivo interaction between BARD1 and PAR with or without the treatment of PJ34 was measured by co-IP and reciprocal co-IP. (G) The in vivo interaction between BARD1 and PAR with or without the treatment of GLTN was measured by co-IP and reciprocal co-IP. (H) The in vivo interaction between WT BRCA1, BRCA1 C61G, or WT BRCA1 with the indicated BARD1 mutants and PAR was measured by co-IP and reciprocal co-IP. Whole cell lysates were blotted and shown as the input (E)-(H). See also Figure S2.
Figure 3
Figure 3. The effect of PARP inhibitor on the recruitment of the BRCA1/BARD1 heterodimer to DNA lesions during early DNA damage response
(A) Representative staining of PAR and γH2AX in cells pretreated by PJ34, GLTN, or PARG knockdown at 1 min or 10 min after laser microirradiation (left). Cells pretreated by PJ34, GLTN, or PARG knockdown were fixed at the indicated time points after laser microirradiation, and the kinetics of PAR staining was examined and summarized in the panel graph (right). (B) The effects of PJ34, GLTN and PARG knockdown on the recruitment of BARD1 BRCTs to DNA damage sites. GFP-BARD1 BRCTs was expressed in U2OS cells pretreated by PJ34, GLTN or PARG knockdown. The relocation of GFP-BARD1 BRCTs was monitored in a time course following laser microirradiation. (C) The effects of PJ34, GLTN and PARG knockdown on the recruitment of BRCA1 to DNA damage sites. GFP-BRCA1 was expressed in U2OS cells pretreated by PJ34, GLTN or PARG knockdown. The relocation of BRCA1 to DNA damage sites was monitored in a time course following laser microirradiation. GFP fluorescence at the laser line was converted into a numerical value (relative fluorescence intensity) using Axiovision software (version 4.5). Normalized fluorescent curves from 20 cells from three independent experiments were averaged. The error bars represent the standard deviation. Scale bar = 10 µm. See also Figure S3.
Figure 4
Figure 4. The recruitment of BRCA1/BARD1 complex to DSB
(A) Schematics of the inducible I-SceI system. TA treatment induces the translocation of RFP-I-SceI-GR fusion protein (red) from the cytoplasm to the nucleus (left). A time course shows the translocation kinetics of RFP-I-SceI-GR from the cytoplasm to the nucleus after TA addition (right). (B) The localization of BRCA1 or BARD1 and PAR before and after TA induction. The DSB (focus) was also marked by γH2AX. Magnified boxes denote the co-localization of BRCA1 or BARD1 with PAR or γH2AX at the DSB. (C) Real time images of the recruitments of GFP-BRCA1, GFP-BARD1 and their GFP-mutants in the inducible I-SceI system. Magnified boxes denote the GFP-fusion proteins at focus. The error bars represent the standard deviation. Scale bar = 10 µm.
Figure 5
Figure 5. Efficacy of PARP inhibitor on cancer-associated BRCA1 and BARD1 mutants
(A) The effect of PJ34 on the recruitment of the P1749R and M1775R mutants of BRCA1 to DNA damage sites. GFP-BRCA1 mutants were expressed in U2OS cells with or without the treatment of PJ34. The relocation of BRCA1 mutants to DNA damage sites was monitored in a time course following laser microirradiation. (B) The effect of PJ34 on the recruitment of the C645R and V695L mutants of BARD1 to DNA damage sites. GFP-BARD1 mutants were expressed in U2OS cells with or without the treatment of PJ34. The relocation of BARD1 mutants to DNA damage sites was monitored in a time course following laser microirradiation. Scale bar = 10 µm. (C) The sensitivities of cells bearing cancer-associated BRCA1 or BARD1 mutants to low dose of IR in the presence or absence of PJ34. (D) The effect of different doses of PJ34 on the cells bearing the P1749R mutant treated by IR. The error bars represent the standard deviation.
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Comment in

References

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