Dottorato in SCIENZE DELLA VITA

Titolo della tesi: Role of APE1/REF-1 (Apurinic/apyrimidinic endonuclease 1/Redox-factor 1) multifunctional protein in the host cellular response to influenza A virus infection

The Apurinic/apyrimidinic endonuclease 1/Redox-factor 1 (APE1/REF-1) is a multifunctional protein involved in the Base Excision Repair (BER) of DNA damage and in the redox activation of transcription factors involved in the inflammatory response, such as NF-κB and AP-1. Some studies have reported a modulatory role of APE1/REF-1 on NRF2, one of the most important regulators of the antioxidant response, but conflicting conclusions have been reached. The modulation of intracellular redox state and the inflammatory response are some of the most important factors contributing to the pathogenesis of respiratory virus infections; however, the role of APE1/REF-1 in the host response to respiratory virus infections has never been explored. The aim of this research project is, therefore, to study the modulation and role of APE1/REF-1 in the host immune response and virus replication during influenza virus infection. Methods: BEAS-2B cells (derived from normal bronchial epithelium obtained from non-cancerous individuals) and A549 cells (adenocarcinoma human alveolar basal epithelial cells) were infected with two different strains of influenza virus (A/Puerto Rico/8/34 H1N1 PR8 and A/Seal/Massachusetts/1/80 H7N7 SC35M). Cells were silenced for APE1/REF-1 (through small interfering RNA) or treated with a specific inhibitor (E3330) of APE1 redox function. The immune response was assessed by measuring the concentration or gene expression of proinflammatory cytokines and chemokines such as IL-6, IL-1β, TNF-α, CCL5 RANTES, Interferon α and β, and Interferon-stimulated genes (ISGs). The redox response was evaluated by assessing the induction of NRF2-regulated gene HMOX1 expression, the GSH/GSSG ratio, and the nuclear translocation of NRF2. Results and Conclusion: Infection with influenza virus resulted in significant downregulation of both NRF2 and APE1/REF-1 at both the protein and mRNA levels. Additionally, APE1/REF-1 knockdown in BEAS-2B cells led to decreased NRF2 expression, suggesting a mechanistic relationship between these two proteins. Furthermore, APE1/REF-1 downregulation affected the host response to infection, leading to reduced pro-inflammatory cytokine production and increased oxidative stress during infection. Notably, APE1/REF-1 inhibition using the E3330 inhibitor also led to decreased pro-inflammatory cytokine induction and increased oxidative stress. Surprisingly, despite the enhanced oxidative stress, E3330 treatment resulted in reduced virus replication and altered expression of viral proteins. These findings suggest that APE1/REF-1 redox activity plays a complex role in regulating the host response to influenza virus infection, impacting both the inflammation and the redox response.