NR4A1 is a HIF-dependent repressor of SLC30A10 transcription that controls manganese homeostasis

The primary mechanism that controls manganese (Mn) homeostasis in mammals is the activation of hypoxia-inducible factor (HIF) transcription factors by elevated Mn, which transcriptionally upregulates expression of the Mn efflux transporter SLC30A10 to reduce cellular/organismal Mn levels. Here, we identify an additional unexpected component of the Mn-induced and HIF-dependent homeostatic response that represses SLC30A10 expression. In cells, (1) Mn treatment upregulated expression of the transcription factor NR4A1 (also called Nur77); (2) NR4A1 knockdown increased SLC30A10 expression and reduced the sensitivity of wildtype, but not ΔSLC30A10, cells to Mn toxicity; and (3) overexpression of NR4A1 reduced SLC30A10 expression and increased sensitivity to Mn toxicity. Thus, NR4A1 is a Mn-responsive gene that contributes to the control of Mn homeostasis by repressing SLC30A10 expression. In addition, (1) in cells, the Mn-induced upregulation of NR4A1 was attenuated by knockdown of both HIF1α and HIF2α and (2) in mice, Mn exposure upregulated expression of NR4A1 in the liver of control or tissue-specific HIF1α but not tissue-specific HIF2α knockout mice. Thus, the induction of NR4A1 by elevated Mn is HIF2 dependent. Collectively, current and prior results imply that the activation of HIF1/HIF2 during elevated Mn exposure has two opposing effects on SLC30A10 expression, direct transcriptional upregulation and indirect repression via NR4A1, that together set SLC30A10 expression to the level necessary to restore cellular Mn to the physiological range. The repressive arm of the HIF-mediated transcriptional cascade that controls SLC30A10 expression may be designed to prevent Mn deficiency, which may otherwise occur from prolonged or excessive upregulation of SLC30A10.