HSV-1 and influenza infection induce linear and circular splicing of the long NEAT1 isoform
The herpes simplex virus 1 (HSV-1) virion host shut-off (vhs) protein cleaves both cellular and viral mRNAs but not circular RNAs (circRNAs) without an internal ribosome entry site. Here, we show that vhs activity leads to an accumulation of circRNAs relative to linear mRNAs during HSV-1 infection. Strikingly, we found that circular splicing of the long isoform (NEAT1_2) of the nuclear paraspeckle assembly transcript 1 (NEAT1) was massively induced during HSV-1 infection in a vhs-independent manner while NEAT1_2 was still bound to the chromatin. This was associated with induction of linear splicing of NEAT1_2 both within and downstream of the circRNA. NEAT1_2 splicing was absent in uninfected cells but can be induced by ectopic co-expression of the HSV-1 immediate-early proteins ICP22 and ICP27. Interestingly, NEAT1_2 circular and linear splicing was also up-regulated in influenza infection but absent in stress conditions, which disrupt transcription termination similar to but not in the same manner as HSV-1 and influenza infection. Finally, large-scale analysis of published RNA-seq data uncovered induction of NEAT1_2 splicing in cancer cells upon inhibition or knockdown of cyclin-dependent kinase 7 (CDK7) or the MED1 subunit of the Mediator complex phosphorylated by CDK7. Interestingly, CDK7 inhibition also disrupted transcription termination, highlighting a possible link between disruption of transcription termination and NEAT1_2 splicing.