Cyclosporin A triggers a RIG-I-mediated interferon response through multiple cellular processes.

The development of broad-spectrum antiviral agents is essential for preparedness against emerging viruses with pandemic potential. Cyclosporin A (CsA), a clinically approved immunosuppressant, has been shown to exert antiviral activity against a wide range of viruses. Recent evidence suggests that this effect is partially mediated through the induction of interferon lambda (IFN-λ), which in turn stimulates a set of interferon-stimulated genes (ISGs) that establish an antiviral cellular state. However, the molecular mechanisms underlying IFN-λ induction by CsA have remained poorly understood. Here, we demonstrate that CsA triggers a retinoic acid-inducible gene I (RIG-I)-dependent activation of the IFN-λ/ISG signaling axis. This is accompanied by the upregulation of mitochondrial double-stranded RNA (dsRNA). Importantly, we show that CsA causes pronounced alterations in the mitochondrial cristae network. CsA also impairs autophagy, as evidenced by reduced autophagosomal membrane formation and increased levels of the autophagy marker p62. Supporting a functional link, treatment with the autophagy inducer Torin-1 reverses CsA-induced dsRNA accumulation, IFN-λ expression and ISG transcription. Together, our data indicate that the antiviral activity of CsA is partially driven by converging cellular processes involving mitochondrial remodeling, dsRNA accumulation, and impaired autophagy, which collectively activate the RIG-I/IFN-λ/ISG axis, offering mechanistic insights with therapeutic implications.