STAT2-dependent induction of RNA adenosine deaminase ADAR1 by type I interferon differs between mouse and human cells in the requirement for STAT1

- We examined the induction of RNA adenosine deaminase ADAR1 by interferon.
- ADAR1 induction was STAT1-independent but STAT2- and IRF9-dependent in mouse cells.
- ADAR1 induction was dependent on both STAT1 and STAT2 in human cells.
- STAT2 bound at the inducible promoter in the absence of STAT1 in Stat1−/− MEFs.
- ADAR1 induction in STAT1-sufficient MEFs was greater than in STAT1 null MEFs.

Expression of adenosine deaminase acting on RNA1 (ADAR1) is driven by alternative promoters. Promoter PA, activated by interferon (IFN), produces transcripts that encode the inducible p150 ADAR1 protein, whereas PB specifies the constitutively expressed p110 protein. We show using Stat1−/−, Stat2−/− and IRF9−/− MEFs that induction of ADAR1 p150 occurs by STAT2- and IRF9-dependent signaling that is enhanced by, but not obligatorily dependent upon, STAT1. Chromatin immunoprecipitation analysis demonstrated STAT2 at the PA promoter in IFN-treated Stat1−/− cells, whereas IFN-treated wild-type cells showed both STAT1 and STAT2 bound at PA. By contrast, with human 2fTGH cells and mutants U3A or U6A, ADAR1 induction by IFN was dependent upon both STAT1 and STAT2. These results suggest that transcriptional activation of Adar1 by IFN occurs in the absence of STAT1 by a non-canonical STAT2-dependent pathway in mouse but not human cells.