The hepatic
hormone hepcidin is a key regulator of systemic
iron metabolism. Its expression is largely regulated by 2 signaling pathways: the "
iron-regulated"
bone morphogenetic protein (BMP) and the inflammatory JAK-STAT pathways. To obtain broader insights into cellular processes that modulate
hepcidin transcription and to provide a resource to identify novel genetic modifiers of systemic
iron homeostasis, we designed an RNA interference (RNAi) screen that monitors
hepcidin promoter activity after the knockdown of 19 599 genes in hepatocarcinoma cells. Interestingly, many of the putative
hepcidin activators play roles in signal transduction,
inflammation, or transcription, and affect
hepcidin transcription through BMP-responsive elements. Furthermore, our work sheds light on new components of the transcriptional machinery that maintain steady-state levels of
hepcidin expression and its responses to the BMP- and interleukin-6-triggered signals. Notably, we discover
hepcidin suppression mediated via components of Ras/RAF MAPK and mTOR signaling, linking
hepcidin transcriptional control to the pathways that respond to
mitogen stimulation and nutrient status. Thus using a combination of RNAi screening, reverse phase
protein arrays, and small molecules testing, we identify links between the control of systemic
iron homeostasis and critical liver processes such as regeneration, response to injury,
carcinogenesis, and nutrient metabolism.