ABSTRACT
Histone H2AX plays a key role in DNA damage signalling in the surrounding regions of DNA double-strand breaks (DSBs). In response to DNA damage, H2AX becomes phosphorylated on serine residue 139 (known as γH2AX), resulting in the recruitment of the DNA repair effectors 53BP1 and BRCA1. Here, by studying resistance to poly(ADP-ribose) polymerase (PARP) inhibitors in BRCA1/2-deficient mammary tumours, we identify a function for γH2AX in orchestrating drug-induced replication fork degradation. Mechanistically, γH2AX-driven replication fork degradation is elicited by suppressing CtIP-mediated fork protection. As a result, H2AX loss restores replication fork stability and increases chemoresistance in BRCA1/2-deficient tumour cells without restoring homology-directed DNA repair, as highlighted by the lack of DNA damage-induced RAD51 foci. Furthermore, in the attempt to discover acquired genetic vulnerabilities, we find that ATM but not ATR inhibition overcomes PARP inhibitor (PARPi) resistance in H2AX-deficient tumours by interfering with CtIP-mediated fork protection. In summary, our results demonstrate a role for H2AX in replication fork biology in BRCA-deficient tumours and establish a function of H2AX separable from its classical role in DNA damage signalling and DSB repair.
Subject(s)
BRCA1 Protein , BRCA2 Protein , DNA Replication , Drug Resistance, Neoplasm , Histones , Poly(ADP-ribose) Polymerase Inhibitors , Animals , Female , Humans , Mice , Ataxia Telangiectasia Mutated Proteins/metabolism , Ataxia Telangiectasia Mutated Proteins/genetics , BRCA1 Protein/metabolism , BRCA1 Protein/deficiency , BRCA1 Protein/genetics , BRCA2 Protein/metabolism , BRCA2 Protein/genetics , BRCA2 Protein/deficiency , Breast Neoplasms/genetics , Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Breast Neoplasms/drug therapy , Carrier Proteins/metabolism , Carrier Proteins/genetics , Cell Line, Tumor , DNA Breaks, Double-Stranded , DNA Damage , DNA Repair , DNA Replication/drug effects , Drug Resistance, Neoplasm/genetics , Histones/metabolism , Poly(ADP-ribose) Polymerase Inhibitors/pharmacology , Rad51 Recombinase/metabolism , Rad51 Recombinase/genetics , Tumor Suppressor p53-Binding Protein 1/metabolism , Tumor Suppressor p53-Binding Protein 1/genetics , Mice, NudeABSTRACT
The persistence of drug-sensitive tumors poses a significant challenge in cancer treatment. The concept of bacterial persisters, which are a subpopulation of bacteria that survive lethal antibiotic doses, is frequently used to compare to residual disease in cancer. Here, we explore drug tolerance of cancer cells and bacteria. We highlight the fact that bacteria, in contrast to cancer cells, have been selected for survival at the population level and may therefore possess contingency mechanisms that cancer cells lack. The precise mechanisms of drug-tolerant cancer cells and bacterial persisters are still being investigated. Undoubtedly, by understanding common features as well as differences, we, in the cancer field, can learn from microbiology to find strategies to eradicate persisting cancer cells.
Subject(s)
Anti-Bacterial Agents , Bacteria , Neoplasms , Humans , Anti-Bacterial Agents/pharmacology , Anti-Bacterial Agents/therapeutic use , Antineoplastic Agents/pharmacology , Antineoplastic Agents/therapeutic use , Bacteria/drug effects , Drug Resistance, Neoplasm/drug effects , Neoplasm, Residual , Neoplasms/drug therapy , Neoplasms/pathologyABSTRACT
In recent years platinum (Pt) drugs have been found to be especially efficient to treat patients with cancers that lack a proper DNA damage response, e.g. due to dysfunctional BRCA1. Despite this knowledge, we are still missing helpful markers to predict Pt response in the clinic. We have previously shown that volume-regulated anion channels, containing the subunits LRRC8A and LRRC8D, promote the uptake of cisplatin and carboplatin in BRCA1-proficient cell lines. Here, we show that the loss of LRRC8A or LRRC8D significantly reduces the uptake of cis- and carboplatin in BRCA1;p53-deficient mouse mammary tumor cells. This results in reduced DNA damage and in vivo drug resistance. In contrast to Lrrc8a, the deletion of the Lrrc8d gene does not affect the viability and fertility of mice. Interestingly, Lrrc8d-/- mice tolerate a two-fold cisplatin maximum-tolerable dose. This allowed us to establish a mouse model for intensified Pt-based chemotherapy, and we found that an increased cisplatin dose eradicates BRCA1;p53-deficient tumors, whereas eradication is not possible in WT mice. Moreover, we show that decreased expression of LRRC8A/D in head and neck squamous cell carcinoma patients, who are treated with a Pt-based chemoradiotherapy, leads to decreased overall survival of the patients. In particular, high cumulative cisplatin dose treatments lost their efficacy in patients with a low LRRC8A/D expression in their cancers. Our data therefore suggest that LRRC8A and LRRC8D should be included in a prospective trial to predict the success of intensified cis- or car-boplatin-based chemotherapy.