DNA polymerase beta expression in head & neck cancer modulates the poly(ADP-ribose)-mediated replication checkpoint

Abstract

Head and Neck Squamous Cell Carcinoma (HNSCC) imposes a significant health burden, necessitating innovative therapeutic strategies to enhance treatment efficacy. Current treatments, such as surgery, radiation, and chemotherapy, have limited effectiveness and yield severe side effects, emphasizing the need for targeted therapies. We have focused on DNA polymerase beta (Polβ) and its roles in replication stress, cellular responses to DNA damaging-therapies, and DNA damage response modifiers. Our investigations reveal a regulatory role for base excision repair (BER) proteins, including Polβ, in the cellular response to inhibitors of poly(ADP-ribose) glycohydrolase (PARG), an enzyme involved in poly(ADP-ribose) (PAR) degradation. The inhibition of PARG, in HNSCC cells, elicits replication stress and activates the PAR-induced S-phase/ATR checkpoint, leading to a block to replication, cell cycle arrest, and the onset of apoptosis. However, Polβ overexpression mitigates this response, reducing replication-stress-induced PAR foci formation, suggesting a modulation of replication checkpoint activation. We found that PARG inhibitor treatment is ineffective on HNSCC cells that overexpress Polβ, implying that the PARG inhibitor-induced PAR and apoptotic response is dependent on the level of Polβ. Further, our in vitro experiments demonstrate that combining PARG and ATR/CHK1 inhibitors overcomes Polβ-mediated treatment resistance in HNSCC cells, producing synergistic effects compared to the individual treatment conditions. Our findings suggest a possible treatment paradigm for HNSCC, employing ATR or CHK1 inhibitors in combination with PARG inhibitors. This strategy offers a promising path for more effective HNSCC treatments, potentially overcoming Polβ-related resistance.