Mitsuaki Sobajima, Masato Miyake, Yoshimasa Hamada, Kazue Tsugawa, Miho Oyadomari, Ryota Inoue, Jun Shirakawa, Hiroshi Arima and Seiichi Oyadomari : The multifaceted role of ATF4 in regulating glucose-stimulated insulin secretion., Biochemical and Biophysical Research Communications, Vol.611, 165-171, 2022.
(Summary)
Stress-inducible transcription factor ATF4 is essential for survival and identity of β-cell during stress conditions. However, the physiological role of ATF4 in β-cell function is not yet completely understood. To understand the role of ATF4 in glucose-stimulated insulin secretion (GSIS), β-cell-specific Atf4 knockout (βAtf4KO) mice were phenotypically characterized. Insulin secretion and mechanistic analyses were performed using islets from control Atf4f/f and βAtf4KO mice to assess key regulators for triggering and amplifying signals for GSIS. βAtf4KO mice displayed glucose intolerance due to reduced insulin secretion. Moreover, βAtf4KO islets exhibited a decrease in both the insulin content and first-phase insulin secretion. The analysis of βAtf4KO islets showed that ATF4 is required for insulin production and glucose-stimulated ATP and cAMP production. The results demonstrate that ATF4 contributes to the multifaceted regulatory process in GSIS even under stress-free conditions.
Tetsuya Bando, Misa Okumura, Yuki Bando, Marou Hagiwara, Yoshimasa Hamada, Yoshiyasu Ishimaru, Taro Mito, Eri Kawaguchi, Takeshi Inoue, Kiyokazu Agata, Sumihare Noji and Hideyo Ohuchi : Toll signalling promotes blastema cell proliferation during cricket leg regeneration via insect macrophages., Development, Vol.149, No.8, 2022.
(Summary)
Hemimetabolous insects, such as the two-spotted cricket Gryllus bimaculatus, can recover lost tissues, in contrast to the limited regenerative abilities of human tissues. Following cricket leg amputation, the wound surface is covered by the wound epidermis, and plasmatocytes, which are insect macrophages, accumulate in the wound region. Here, we studied the function of Toll-related molecules identified by comparative RNA sequencing during leg regeneration. Of the 11 Toll genes in the Gryllus genome, expression of Toll2-1, Toll2-2 and Toll2-5 was upregulated during regeneration. RNA interference (RNAi) of Toll, Toll2-1, Toll2-2, Toll2-3 or Toll2-4 produced regeneration defects in more than 50% of crickets. RNAi of Toll2-2 led to a decrease in the ratio of S- and M-phase cells, reduced expression of JAK/STAT signalling genes, and reduced accumulation of plasmatocytes in the blastema. Depletion of plasmatocytes in crickets using clodronate also produced regeneration defects, as well as fewer proliferating cells in the regenerating legs. Plasmatocyte depletion also downregulated the expression of Toll and JAK/STAT signalling genes in the regenerating legs. These results suggest that Spz-Toll-related signalling in plasmatocytes promotes leg regeneration through blastema cell proliferation by regulating the Upd-JAK/STAT signalling pathway.
Keisuke Kitakaze, Miho Oyadomari, Jun Zhang, Yoshimasa Hamada, Yasuhiro Takenouchi, Kazuhito Tsuboi, Mai Inagaki, Masanori Tachikawa, Yoshio Fujitani, Yasuo Okamoto and Seiichi Oyadomari : ATF4-mediated transcriptional regulation protects against β-cell loss during endoplasmic reticulum stress in a mouse model., Molecular Metabolism, Vol.54, 2021.
(Summary)
We conclude that transcriptional regulation by ATF4 maintains β-cell identity via ISR modulation. This mechanism provides a promising target for the treatment of diabetes.
The integrated stress response (ISR) is one of the most important cytoprotective mechanisms and is integrated by phosphorylation of the α subunit of eukaryotic translation initiation factor 2 (eIF2α). Four eIF2α kinases, heme-regulated inhibitor (HRI), double-stranded RNA-dependent protein kinase (PKR), PKR-like endoplasmic reticulum kinase (PERK), and general control nonderepressible 2 (GCN2), are activated in response to several stress conditions. We previously reported that nanosecond pulsed electric fields (nsPEFs) are a potential therapeutic tool for ISR activation. In this study, we examined which eIF2α kinase is activated by nsPEF treatment. To assess the responsible eIF2α kinase, we used previously established eIF2α kinase quadruple knockout (4KO) and single eIF2α kinase-rescued 4KO mouse embryonic fibroblast (MEF) cells. nsPEFs 70 ns in duration with 30 kV/cm electric fields caused eIF2α phosphorylation in wild-type (WT) MEF cells. On the other hand, nsPEF-induced eIF2α phosphorylation was completely abolished in 4KO MEF cells and was recovered by HRI overexpression. CM-H2DCFDA staining showed that nsPEFs generated reactive oxygen species (ROS), which activated HRI. nsPEF-induced eIF2α phosphorylation was blocked by treatment with the ROS scavenger N-acetyl-L-cysteine (NAC). Our results indicate that the eIF2α kinase HRI is responsible for nsPEF-induced ISR activation and is activated by nsPEF-generated ROS.
M Alexandra Stevens, Michael Xiang, N Lisa Heppler, Isidora Tošić, Kevin Jiang, O Jaime Munoz, S Amos Gaikwad, M Terzah Horton, Xin Long, Padmini Narayanan, L Elizabeth Seashore, C Maci Terrell, Raushan Rashid, J Michael Krueger, E Alicia Mangubat-Medina, T Zachary Ball, Pavel Sumazin, R Sarah Walker, Yoshimasa Hamada, Seiichi Oyadomari, S Michele Redell and A David Frank : Atovaquone is active against AML by upregulating the integrated stress pathway and suppressing oxidative phosphorylation., Blood Advances, Vol.3, No.24, 4215-4227, 2019.
(Summary)
Atovaquone, a US Food and Drug Administration-approved antiparasitic drug previously shown to reduce interleukin-6/STAT3 signaling in myeloma cells, is well tolerated, and plasma concentrations of 40 to 80 µM have been achieved with pediatric and adult dosing. We conducted preclinical testing of atovaquone with acute myeloid leukemia (AML) cell lines and pediatric patient samples. Atovaquone induced apoptosis with an EC50 <30 µM for most AML lines and primary pediatric AML specimens. In NSG mice xenografted with luciferase-expressing THP-1 cells and in those receiving a patient-derived xenograft, atovaquone-treated mice demonstrated decreased disease burden and prolonged survival. To gain a better understanding of the mechanism of atovaquone, we performed an integrated analysis of gene expression changes occurring in cancer cell lines after atovaquone exposure. Atovaquone promoted phosphorylation of eIF2α, a key component of the integrated stress response and master regulator of protein translation. Increased levels of phosphorylated eIF2α led to greater abundance of the transcription factor ATF4 and its target genes, including proapoptotic CHOP and CHAC1. Furthermore, atovaquone upregulated REDD1, an ATF4 target gene and negative regulator of the mechanistic target of rapamycin (mTOR), and caused REDD1-mediated inhibition of mTOR activity with similar efficacy as rapamycin. Additionally, atovaquone suppressed the oxygen consumption rate of AML cells, which has specific implications for chemotherapy-resistant AML blasts that rely on oxidative phosphorylation for survival. Our results provide insight into the complex biological effects of atovaquone, highlighting its potential as an anticancer therapy with novel and diverse mechanisms of action, and support further clinical evaluation of atovaquone for pediatric and adult AML.
Keisuke Kitakaze, Shusuke Taniuchi, Eri Kawano, Yoshimasa Hamada, Masato Miyake, Miho Oyadomari, Hirotatsu Kojima, Hidetaka Kosako, Tomoko Kuribara, Suguru Yoshida, Takamitsu Hosoya and Seiichi Oyadomari : Cell-based HTS identifies a chemical chaperone for preventing ER protein aggregation and proteotoxicity., eLife, Vol.8, e43302, 2019.
(Summary)
]benzothiazole derivatives (IBTs) as chemical chaperones in a cell-based high-throughput screen. Biochemical and chemical biology approaches revealed that IBT21 directly binds to unfolded or misfolded proteins and inhibits protein aggregation. Finally, IBT21 prevented cell death caused by chemically induced ER stress and by a proteotoxin, an aggression-prone prion protein. Taken together, our data show the promise of IBTs as potent chemical chaperones that can ameliorate diseases resulting from protein aggregation under ER stress.
Yoshimasa Hamada, Atsushi Tokuoka, Tetsuya Bando, Hideyo Ohuchi and Kenji Tomioka : Enhancer of zeste plays an important role in photoperiodic modulation of locomotor rhythm in the cricket, Gryllus bimaculatus., Zoological Letters, Vol.2, 2016.
(Summary)
These results suggest that histone modification by Gb'E(z) is involved in photoperiodic modulation of the G. bimaculatus circadian rhythm.
Akira Izutani, Yuji Furumoto, Yoshimasa Hamada, Masato Miyake, Kenji Teranishi, Naoyuki Shimomura and Seiichi Oyadomari : The Influence of Applying High Electrical Field Pulses on Unfolded Protein Response of cells, The 2019 IEEE Pulsed Power and Plasma Science Conference, 4-pages, Orlando, Jun. 2019.