TY - JOUR
T1 - Replication gaps underlie BRCA deficiency and therapy response
AU - Panzarino, Nicholas J.
AU - Krais, John J.
AU - Cong, Ke
AU - Peng, Min
AU - Mosqueda, Michelle
AU - Nayak, Sumeet U.
AU - Bond, Samuel M.
AU - Calvo, Jennifer A.
AU - Doshi, Mihir B.
AU - Bere, Matt
AU - Ou, Jianhong
AU - Deng, Bin
AU - Zhu, Lihua J.
AU - Johnson, Neil
AU - Cantor, Sharon B.
N1 - Publisher Copyright:
©2020 American Association for Cancer Research.
PY - 2021/3/1
Y1 - 2021/3/1
N2 - Defects in DNA repair and the protection of stalled DNA replication forks are thought to underlie the chemosensitivity of tumors deficient in the hereditary breast cancer genes BRCA1 and BRCA2 (BRCA). Challenging this assumption are recent findings that indicate chemotherapies, such as cisplatin used to treat BRCA-deficient tumors, do not initially cause DNA double-strand breaks (DSB). Here, we show that ssDNA replication gaps underlie the hypersensitivity of BRCA-deficient cancer and that defects in homologous recombination (HR) or fork protection (FP) do not. In BRCA-deficient cells, ssDNA gaps developed because replication was not effectively restrained in response to stress. Gap suppression by either restoration of fork restraint or gap filling conferred therapy resistance in tissue culture and BRCA patient tumors. In contrast, restored FP and HR could be uncoupled from therapy resistance when gaps were present. Moreover, DSBs were not detected after therapy when apoptosis was inhibited, supporting a framework in which DSBs are not directly induced by genotoxic agents, but rather are induced from cell death nucleases and are not fundamental to the mechanism of action of genotoxic agents. Together, these data indicate that ssDNA replication gaps underlie the BRCA cancer phenotype, “BRCAness,” and we propose they are fundamental to the mechanism of action of genotoxic chemotherapies. Significance: This study suggests that ssDNA replication gaps are fundamental to the toxicity of genotoxic agents and underlie the BRCA-cancer phenotype “BRCAness,” yielding promising biomarkers, targets, and opportunities to resensitize refractory disease.
AB - Defects in DNA repair and the protection of stalled DNA replication forks are thought to underlie the chemosensitivity of tumors deficient in the hereditary breast cancer genes BRCA1 and BRCA2 (BRCA). Challenging this assumption are recent findings that indicate chemotherapies, such as cisplatin used to treat BRCA-deficient tumors, do not initially cause DNA double-strand breaks (DSB). Here, we show that ssDNA replication gaps underlie the hypersensitivity of BRCA-deficient cancer and that defects in homologous recombination (HR) or fork protection (FP) do not. In BRCA-deficient cells, ssDNA gaps developed because replication was not effectively restrained in response to stress. Gap suppression by either restoration of fork restraint or gap filling conferred therapy resistance in tissue culture and BRCA patient tumors. In contrast, restored FP and HR could be uncoupled from therapy resistance when gaps were present. Moreover, DSBs were not detected after therapy when apoptosis was inhibited, supporting a framework in which DSBs are not directly induced by genotoxic agents, but rather are induced from cell death nucleases and are not fundamental to the mechanism of action of genotoxic agents. Together, these data indicate that ssDNA replication gaps underlie the BRCA cancer phenotype, “BRCAness,” and we propose they are fundamental to the mechanism of action of genotoxic chemotherapies. Significance: This study suggests that ssDNA replication gaps are fundamental to the toxicity of genotoxic agents and underlie the BRCA-cancer phenotype “BRCAness,” yielding promising biomarkers, targets, and opportunities to resensitize refractory disease.
UR - http://www.scopus.com/inward/record.url?scp=85099370335&partnerID=8YFLogxK
U2 - 10.1158/0008-5472.CAN-20-1602
DO - 10.1158/0008-5472.CAN-20-1602
M3 - Article
C2 - 33184108
AN - SCOPUS:85099370335
SN - 0008-5472
VL - 81
SP - 1388
EP - 1397
JO - Cancer research
JF - Cancer research
IS - 5
ER -