VDR and idiopathic pulmonary fibrosis: 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).