Endoplasmic Reticulum Aminopeptidase 1 (ERAP1) is a multifunctional enzyme belonging to the M1 family of aminopeptidases and shown to be associated with various autoimmune diseases. Human ERAP1 protein has two isoforms produced by alternative splicing of the 3' terminal exon, although their functional differences have not yet been fully clarified. In this study, we showed that the isoforms undergo different posttranscriptional regulation mechanisms via their respective 3' untranslated regions. Using a reporter system, we identified several cis-elements that are important for the regulation of alternative splicing. Finally, we revealed a close relationship between the transcriptional induction of the ERAP1 gene by interferon-gamma and the alternative splicing. These results suggest that the two ERAP1 isoforms function under different pathophysiological conditions. (C) 2018 Published by Elsevier Inc.