EXOSC5 and idiopathic pulmonary fibrosis: Furthermore, promoter analysis of the same MIRLET7D targets by chromatin immunoprecipitation (ChIP; Fig. 2c) showed decreased levels of various subunits of the RNA exosome complex (EXOSC10, EXOSC5, and EXOSC1), the heterochromatin mark H3K27me3 (trimethylated Lys-27 of histone 3), and the enzyme mediating this histone modification (EZH2), whereas the levels of transcription initiating S5 phosphorylated RNA polymerase II (POLII) increased in IPF, compared with Ctrl fibroblasts.