Transcriptional activation of hepcidin by the microphthalmia/transcription factor E family

Abstract

Hepcidin negatively regulates the circulating iron levels by inhibiting the intestinal absorption of iron as well as iron release from macrophages. Hepcidin activity is largely determined by its expression, which is regulated at the transcriptional level. Hepcidin transcription is induced not only by the iron status‐related bone morphogenetic protein (BMP)‐2/6, but also by inflammatory cytokines, such as interleukin (IL)‐1β and IL‐6. The present study reveals that the microphthalmia (MiT)/transcription factor E (TFE) family members are novel regulators of hepcidin transcription. Melanocyte‐inducing transcription factor (MITF)‐A, a member of the MiT/TFE family, was identified as a positive regulator of hepcidin transcription via stimulus screening for transcription regulators. An E‐box (5′‐CATGTG‐3′) spanning nt‐645 to nt‐640 of the murine hepcidin promoter was identified as an MITF‐A‐responsive element. Responsiveness to MITF‐A on hepcidin transcription decreased when the cells were stimulated with BMP2 or IL‐1β. These results suggest a functional interaction between the MITF pathway and BMP‐ or IL‐1β‐mediated signaling. TFEB and TFE3, members of the MiT/TFE family, also stimulated hepcidin transcription, but the main region responsible for hepcidin transcription was distinct from that induced by MITF‐A. The region spanning nt‐581 to nt‐526 was involved in TFEB/TFE3‐mediated hepcidin transcription. Considering that members of the MiT/TFE family act as regulators of starvation‐induced lysosomal biogenesis, hepcidin expression may be controlled by additional pathways apart from those identified so far.

Regulatory mechanisms underlying interleukin‐6 expression in murine brown adipocytes

“…Next, we explored the stimulatory factors for IL‐6 transcription using SSRT, a luciferase‐based screening of modulators of target gene transcription 44,45 . Because the transfection efficiency was low in HB2 brown adipogenic cells (data not shown), SSRT was performed in C2C12 myogenic cells (Figure 5A).…”

“…The murine IL‐6 enhancer region spanning nt ‐2978 to nt +1 (+1: translational initiation site), was cloned into pGL4 to generate IL‐6(‐2978)‐luc. Luciferase‐based SSRT was performed as described previously 44,45 . The expression vectors used in the stimulus SSRT are listed in Supporting Information: Table S6.…”

“…Luciferase-based SSRT was performed as described previously. 44,45 The expression vectors used in the stimulus SSRT are listed in Supporting Information: Table S6. Briefly, C2C12 cells were transfected with the indicated expression vector and reporter plasmid using the polyethylenimine Max reagent.…”

“…Next, we explored the stimulatory factors for IL-6 transcription using SSRT, a luciferase-based screening of modulators of target gene transcription. 44,45 Because the transfection efficiency was low in HB2 brown adipogenic cells (data not shown), SSRT was performed in C2C12 myogenic cells (Figure 5A). The seven molecules, that is, Src, C/EBPβ isoform LAP2, PEBP2-β2, SMAD2, Fyn (an Src family member), constitutively active ALK1, and PGC-1α, increased luciferase activity by more than eightfold compared with luciferase activity in cells transfected with the empty vector (pcDNA3).…”

Upregulation of ATP6V0D2 benefits intracellular survival of Leishmania donovani in erythrocytes-engulfing macrophages

“…Following the internalization process, FPN mainly localizes in early endosome and lysosome ( Sabelli et al., 2017 ) which directly consist or have close contact with Leishmania parasitophorous vacuoles. Furthermore, it is also worthy notice that hepcidin is secreted by macrophages and it shares a common transcription factor TFEB with Atp6v0d2 ( Sow et al., 2007 ; Matsumura et al., 2022 ). It suggests that these molecules are expressed parallelly to facilitate the endosomal/lysosomal transportation of free iron and benefit Leishmania parasites for survival within hemophagocytic macrophages.…”