Inam Ullah KHAN, Gabriel BROOKS, Abdus Saboor SHAH, Yutao ZHANG, Fang GUO
Turkish Journal of Immunology - 2026;14(1):15-23
Objective: Fine-tuned control of interferon (IFN) induction is crucial for triggering an effective immune response that can resolve infection without causing host pathology. Apoptotic caspases (caspase-3 and caspase-9) negatively regulate virus-induced cytokine production and maintain immune homeostasis against viral infection by cleaving cyclic GMP-AMP synthase (cGAS) and interferon regulatory factor 3 (IRF3) in the cGAS-STING pathway. However, continuous unchecked suppression of interferons by these caspases would compromise innate immunity against infection. Here, we report that caspase-3 and caspase-9 themselves are regulated by asparagine endopeptidase (AEP) to maintain basal IFN levels. Materials and Methods: We investigated the expression of IFN- beta, cGAS, and IRF3, and the activity of caspase-3 and caspase-9, in vitro in wild-type (WT) and AEP-/- RAW 264.7 cells in response to vaccinia virus (VACV) infection. Results: AEP-/- RAW 264.7 cells showed significantly diminished levels of IFN- beta, cGAS, and IRF3, and higher caspase-3 and caspase-9 activity in vitro in response to VACV infection. AEP-null mice were more susceptible to VACV, and all (n=7) AEP-deficient mice succumbed to VACV on day 4, compared to WT mice, which died on day 7. This was associated with higher viral loads in the lungs (p=0.0042) and the spleen (p=0.001), and with significantly lower IFN-beta levels ( p=0.0018) in sera from AEP-null mice. Conclusion: We conclude that AEP suppresses the expression and activity of caspase-3 and caspase-9 and protects cGAS and IRF3 from being completely cleaved by these apoptotic caspases. This mechanism maintains basal type I IFN production.
