Biology subjects

Cantor, S.

Publications and source records attributed to Cantor, S..

5 recordsLinked to original sources

bioRxiv2024

FANCJ promotes PARP1 activity during DNA replication that is essential in BRCA1 deficient cells

Single-stranded DNA gaps are postulated to be fundamental to the mechanism of anti-cancer drugs. Gaining insights into their induction could therefore be pivotal for advancing therapeutic strategies. For poly (ADP-ribose) polymerase inhibitors (PARPi) to be effective, the presence of FANCJ helicase is required. However, the relationship between FANCJ dependent gaps and PARP1 catalytic inhibition or trapping--both linked to PARPi toxicity in BRCA deficient cells--is yet to be elucidated. Here, we find that the efficacy of PARPi is contingent on S-phase PARP1 activity, which is compromised in FANCJ deficient cells because PARP1, along with MSH2, is "sequestered" by G-quadruplexes. PARP1s replication activity is also diminished in cells missing a FANCJ-MLH1 interaction, but in such cells, depleting MSH2 can release sequestered PARP1, restoring PARPi-induced gaps and sensitivity. Our observations indicate that sequestered and trapped PARP1 are different chromatin-bound forms, with FANCJ loss increasing PARPi resistance in cells susceptible to canonical PARP1 trapping. However, in BRCA1 null cells, the loss of FANCJ mirrors the effects of PARP1 loss or inhibition, with the common detrimental factor being the loss of PARP1 activity during DNA replication, not trapping. These insights underline the crucial role of PARP1 activity during DNA replication in BRCA deficient cells and emphasize the importance of understanding drug mechanisms for enhancing precision medicine.

molecular biology↗

bioRxiv2021

Loss of Nuclear DNA ligase III Can Revert PARP Inhibitor Resistance in BRCA1-deficient Cells by Increasing DNA Replication Stress

Inhibitors of poly(ADP-ribose) (PAR) polymerase (PARPi) have entered the clinic for the treatment of homologous recombination (HR)-deficient cancers. Despite the success of this approach, preclinical and clinical research with PARPi has revealed multiple resistance mechanisms, highlighting the need for identification of novel functional biomarkers and combination treatment strategies. Functional genetic screens performed in cells and organoids that acquired resistance to PARPi by loss of 53BP1 identified loss of LIG3 as an enhancer of PARPi toxicity in BRCA1-deficient cells. Enhancement of PARPi toxicity by LIG3 depletion is dependent on BRCA1 deficiency but independent of the loss of 53BP1 pathway. Mechanistically, we show that LIG3 loss promotes formation of MRE11-mediated post-replicative ssDNA gaps in BRCA1-deficient and BRCA1/53BP1 double-deficient cells exposed to PARPi, leading to an accumulation of chromosomal abnormalities. LIG3 depletion also enhances efficacy of PARPi against BRCA1-deficient mammary tumors in mice, suggesting LIG3 as a potential therapeutic target.

cancer biology↗

bioRxiv2019

Replication gaps underlie BRCA-deficiency and therapy response

Cancers that are deficient in BRCA1 or BRCA2 are hypersensitive to genotoxic agents, including platinums and other first-line chemotherapeutics. The established models propose that these cancers are hypersensitive because the chemotherapies block or degrade DNA replication forks and thereby create DNA double strand breaks, both of which require functional BRCA proteins to prevent or resolve by mechanisms termed fork protection (FP) or homologous recombination (HR). However, recent findings challenge this dogma because genotoxic agents do not initially cause DNA double strand breaks or stall replication forks. Here, we propose a new model for genotoxic chemotherapy in which ssDNA replication gaps underlie the hypersensitivity of BRCA deficient cancer, and we propose that defects in HR or FP do not. Specifically, we observed that ssDNA gaps develop in BRCA deficient cells because DNA replication is not effectively restrained in response to genotoxic stress. Moreover, we observe gap suppression (GS) by either restored fork restraint or by gap filling, both of which conferred resistance to therapy in tissue culture and BRCA patient tumors. In contrast, restored HR and FP were not sufficient to prevent hypersensitivity if ssDNA gaps were not eliminated. Together, these data suggest that ssDNA replication gaps underlie the BRCA cancer phenotype, \"BRCAness,\" and we propose are fundamental to the mechanism of action of genotoxic chemotherapies.

cancer biology↗

bioRxiv2019

PARPi synthetic lethality derives from replication-associated single-stranded DNA gaps

BRCA1 or BRCA2 (BRCA)-deficient tumor cells have defects in DNA double strand break repair by homologous recombination (HR) and fork protection (FP) that are thought to underlie the sensitivity to poly(ADP-ribose) polymerase inhibitor (PARPi). Given the recent finding that PARPi accelerates DNA replication, it was proposed that high speed DNA replication leads to DNA double strand breaks (DSBs). Here, we tested the alternative hypothesis that PARPi sensitivity in BRCA deficient cells results from combined replication dysfunction that causes a lethal accumulation of replication-associated single-stranded DNA (ssDNA) gaps. In support of a gap toxicity threshold, PARPi-induced ssDNA gaps accumulate more excessively in BRCA deficient cells and are suppressed in de novo and genetic models of PARPi resistance while defects in HR or FP often lack this correlation. We also uncouple replication speed from lethality. The clear link between PARPi sensitivity and ssDNA gaps provides a new paradigm for understanding synthetic lethal interactions.

cancer biology↗

bioRxiv2019

Replication gaps are a cancer vulnerability counteracted by translesion synthesis

The replication stress response which serves as an anti-cancer barrier is activated not only by DNA damage and replication obstacles, but also oncogenes, mystifying how cancer evolves. Here, we identify that oncogene expression, similar to cancer therapies, induces single stranded DNA (ssDNA) gaps that reduce cell fitness, unless suppressed by translesion synthesis (TLS). DNA fiber analysis and electron microscopy reveal that TLS restricts replication fork slowing, reversal, and fork degradation without inducing replication fork gaps. Evidence that TLS gap suppression is fundamental to cancer, a small molecule inhibitor targeting the TLS factor, REV1, not only disrupts DNA replication and cancer cell fitness, but also synergizes with gap-inducing therapies. This work illuminates that gap suppression during replication is critical for cancer cell fitness and therefore a targetable vulnerability.

cancer biology↗