Regulation of the fatty acid synthase promoter by liver X receptor α through direct and indirect mechanisms in goat mammary epithelial cells

Fatty acid synthase (FASN) is a central enzyme of milk fat synthesis in the ruminant mammary gland. However, the mechanisms regulating goat FASN transcription remain elusive. The objective of this study was to investigate the mechanisms by which liver X receptor α (LXRα) regulates the FASN promoter in goat mammary epithelial cells (GMECs). In this study, T0901317 (T09), an agonist for LXRα, significantly enhanced the mRNA expression and promoter activity of FASN. Cloning of the dairy goat FASN promoter revealed the presence of one LXR response element (LXRE) and two sterol regulatory elements (SREs). Deletion or mutation of the FASN promoter LXRE reduced, but did not eliminate the transcriptional response of FASN to T09. While the LXRE and the SREs were both disrupted, basal transcription was severely reduced and there was no response to T09 treatment. This suggested that a complete response required one LXRE and two SREs. Knockdown of LXRα by siRNA did not alter the basal or T09-induced transcriptional activity of FASN. However, when sterol regulatory binding protein 1 (SREBP1) was knocked down, T09 significantly increased FASN transcription by wild-type GMECs, but had no effect on cells with LXRE-mutant promoters. The results suggested that LXR regulates FASN promoter activity through direct interaction with the LXRE as well as through increasing SREBP1 abundance. The present study provides insight into the transcriptional regulatory mechanisms controlling de novo fatty acid synthesis in GMECs.