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.

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Previous studies suggest a negative relationship between hepatic oxidative stress and productivity in beef cattle. Uncoupling protein 2 (UCP2) is involved in the disappearance of reactive oxygen species, suggesting the defensive role of UCP2 against oxidative stress. The present study examined the relationship between oxidative stress and expression levels of UCP2/Ucp2 in cultured human and mouse liver-derived cells. We also explored factors regulating bovine Ucp2 transcription. As oxidative stress inducers, hydrogen peroxide, ethanol, and cumene hydroperoxide (CmHP) were used. Expression levels of hemoxygenase 1 (HMOX1), a representative gene induced by oxidative stress, were not affected by any oxidative stress inducers in HepG2 human liver-derived cells. The levels of UCP2 mRNA were also unaffected by the oxidative stress inducers. Treatment with CmHP increased expression of Hmox1 in Hepa1-6 mouse liver-derived cells, but Ucp2 expression was not changed. Stimulus screening for regulator of transcription (SSRT) revealed that expression of p50 or p65, transcription factors conferring response to oxidative stress, did not stimulate bovine Ucp2 transcrition in HepG2 cells. SSRT also showed 11 molecules that induced Ucp2 transcription more than 4-fold; among them, endoplasmic reticulum (ER) stress-related transcription factors such as XBP1, c-JUN, JUNB, and C/EBPβ were identified. However, treatment with ER stress inducers did not increase Ucp2 expression in HepG2 and Hepa1-6 cells. The present results suggest that 1) neither oxidative stress nor ER stress induces Ucp2 expression in liver-derived cells, and 2) Ucp2 transcription is stimulated by several transcription factors.

Uncoupling protein 1 (UCP1) is responsible for non-shivering thermogenesis in brown/beige adipocytes in humans and rodents. Previously, we showed unexpected expression of UCP1 in bovine skeletal muscles. Here we evaluated Ucp1 mRNA levels in the muscle tissue of Japanese Black steers. Expression of Ucp1 was higher in 30-month-old cattle than in 26-month-old cattle. Levels of myosin heavy chain (Myh)1, an MYH predominantly expressed in fast-twitch muscles, were also significantly higher in cattle aged 30 months. A similar tendency was observed in the expression of other Myhs that are highly expressed in fast-twitch muscles, Myh2 and Myh4. Ucp1 expression was positively correlated with expression of Myh1, Myh2, and Myh4. Our results indicate the possibility of Ucp1 expression in fast-twitch muscle fibers.