These include FOXD1, a transcription factor that regulates IPF-associated genes such as galectin-3 (30), as well as 2 nuclear receptors, the pregnane X receptor and the vitamin D receptor, both of which can bind DNA as heterodimers with retinoic acid receptors (31–34), which are strongly implicated in mucin gene regulation (35, 36). Here, NR1I2 is linked to idiopathic pulmonary fibrosis.