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Though RNAi and RNA-splicing machineries are involved in regulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication, their precise roles in coronavirus disease 2019 (COVID-19) pathogenesis remain unclear. Herein, we show that decreased RNAi component (Dicer and XPO5) and splicing factor (SRSF3 and hnRNPA3) expression correlate with increased COVID-19 severity. SARS-CoV-2 N protein induces the autophagic degradation of Dicer, XPO5, SRSF3, and hnRNPA3, inhibiting miRNA biogenesis and RNA splicing and triggering DNA damage, proteotoxic stress, and pneumonia. Dicer, XPO5, SRSF3, and hnRNPA3 knockdown increases, while their overexpression decreases, N protein-induced pneumonia's severity. Older mice show lower expression of Dicer, XPO5, SRSF3, and hnRNPA3 in their lung tissues and exhibit more severe N protein-induced pneumonia than younger mice. PJ34, a poly(ADP-ribose) polymerase inhibitor, or anastrozole, an aromatase inhibitor, ameliorates N protein- or SARS-CoV-2-induced pneumonia by restoring Dicer, XPO5, SRSF3, and hnRNPA3 expression. These findings will aid in developing improved treatments for SARS-CoV-2-associated pneumonia. Here, the authors provide evidence that SARS-CoV-2 N protein leads to autophagic degradation of Dicer, XPO5, SRSF3, and hnRNPA3, inducing DNA damage and proteotoxic stress, eventually causing pneumonia. The small-molecule drug PJ34 or anastrozole alleviates N protein-induced pneumonia. [ABSTRACT FROM AUTHOR]

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is a major mediator of inflammation following stimulation with >45 bp double-stranded DNA (dsDNA). Herein, we identify a class of ∼20–40 bp small cytosolic dsDNA (scDNA) molecules that compete with long dsDNA (200–1,500 bp herring testis [HT]-DNA) for binding to cGAS, thus repressing HT-DNA-induced cGAS activation. The scDNA promotes cGAS and Beclin-1 interaction, releasing Rubicon, a negative regulator of phosphatidylinositol 3-kinase class III (PI3KC3), from the Beclin-1-PI3KC3 complex. This leads to PI3KC3 activation and induces autophagy, causing degradation of STING and long cytosolic dsDNA. Moreover, DNA damage decreases, and autophagy inducers increase scDNA levels. scDNA transfection and treatment with autophagy inducers attenuate DNA damage-induced cGAS activation. Thus, scDNA molecules serve as effective brakes for cGAS activation, preventing excessive inflammatory cytokine production following DNA damage. Our findings may have therapeutic implications for cytosolic DNA-associated inflammatory diseases. [Display omitted] • Small cytosolic dsDNA (scDNA) molecules of 20–40 bp exist in human and mouse cells • scDNA represses cGAS activation by competing with long dsDNA and induces autophagy • Downregulation of scDNA facilitates cGAS-STING activation following DNA damage • Autophagy inducers upregulate scDNA and repress DNA damage-induced cGAS activation Liu et al. identify a class of 20–40 bp small cytosolic dsDNAs that prevent cGAS activation by competing with long dsDNA and induce autophagy. In this way, scDNA prevents excessive inflammatory cytokine production following long cytosolic DNA stimulation. [ABSTRACT FROM AUTHOR]