A KDM6 inhibitor potently induces ATF4 and its target gene expression through HRI activation and by UTX inhibition.

UTX/KDM6A encodes a major histone H3 lysine 27 (H3K27) demethylase, and is frequently mutated in various types of human cancers. Although UTX appears to play a crucial role in oncogenesis, the mechanisms involved are still largely unknown. Here we show that a specific pharmacological inhibitor of H3K27 demethylases, GSK-J4, induces the expression of transcription activating factor 4 (ATF4) protein as well as the ATF4 target genes (e.g. PCK2, CHOP, REDD1, CHAC1 and TRIB3). ATF4 induction by GSK-J4 was due to neither transcriptional nor post-translational regulation. In support of this view, the ATF4 induction was almost exclusively dependent on the heme-regulated eIF2α kinase (HRI) in mouse embryonic fibroblasts (MEFs). Gene expression profiles with UTX disruption by CRISPR-Cas9 editing and the following stable re-expression of UTX showed that UTX specifically suppresses the expression of the ATF4 target genes, suggesting that UTX inhibition is at least partially responsible for the ATF4 induction. Apoptosis induction by GSK-J4 was partially and cell-type specifically correlated with the activation of ATF4-CHOP. These findings highlight that the anti-cancer drug candidate GSK-J4 strongly induces ATF4 and its target genes via HRI activation and raise a possibility that UTX might modulate cancer formation by regulating the HRI-ATF4 axis.

Supplementation of all trans retinoic acid ameliorates ethanol-induced endoplasmic reticulum stress.

CONTEXT: Molecular pathogenesis of chronic alcoholism is linked to increased endoplasmic reticulum stress. Ethanol is a competitive inhibitor of vitamin A metabolism and vitamin A supplementation aggravates existing liver problems. Hence, we probed into the impact of supplementation of all trans retinoic acid (ATRA), the active metabolite of vitamin A on ethanol-induced endoplasmic reticulcum stress. METHODS: Male Sprague-Dawley rats were divided into four groups - I: Control; II: Ethanol; III: ATRA; IV: ATRA + Ethanol. After 90 days the animals were sacrificed to study markers of lipid peroxidation in hepatic microsomal fraction and expression of ER stress proteins and apoptosis in liver. RESULTS AND CONCLUSION: Ethanol caused hepatic hyperlipidemia, enhanced microsomal lipid peroxidation, upregulated expression of unfolded protein response associated proteins and that of apoptosis. Ethanol also led to downregulation of retinoid receptors. ATRA supplementation reversed all these alterations indicating the decrease in ethanol-induced endoplasmic reticulum stress.

Tetracyclines cause cell stress-dependent ATF4 activation and mTOR inhibition.

Tetracyclines have long been used as valuable broad-spectrum antibiotics. The high antibacterial activity of tetracyclines, combined with their good tolerability, has led to their widespread use in treating various infectious diseases. However, similar to other antibiotics, tetracyclines are also known for their adverse effects on different human tissues, including hepatic steatosis. We observed that tetracyclines, including doxycycline and minocycline, caused enhanced expression of the liver chalone inhibin ßE in HepG2 cells, mediated by the cell stress-regulated transcription factor ATF4. ATF4 and its target genes ATF3, CHOP, and inhibin ßE are involved in cell cycle control, cell survival, cell metabolism, and modulation of cytokine expression. Furthermore, we observed that long term tetracycline incubation also caused inhibition of the mTOR complex, a central regulator of cell metabolism, further contributing to the observed cell-cycle arrest and autophagy in doxycycline- and minocycline-treated cell lines. ATF4 activation and mTOR inhibition link two crucial regulators of the cellular stress response and cell metabolism to the effects of tetracyclines on eukaryotic cell metabolism, and may help to understand the antibiotic-independent influence of these drugs on human tissues. Since the observed effects of tetracyclines on human cells were also found to be dependent on the magnesium ion concentrations supplied, the data further indicate the importance of magnesium supplementation to reduce or prevent side effects of long term treatment with tetracyclines.

Concentrated bovine milk whey active proteins facilitate osteogenesis through activation of the JNK-ATF4 pathway.

Concentrated fractions of low molecular weight whey proteins (1-30 kDa), that is concentrated bovine milk whey active proteins (CBP), have been found to enhance bone formation in both in vivo and clinical studies, but the underlying mechanisms are poorly understood. In this study, we found that CBP promoted osteoblastic differentiation in normal human osteoblasts, and determined the involvement of the c-jun NH2-terminal kinase (JNK)-activating transcription factor 4 (ATF4) pathway. We observed that alkaline phosphatase activity and mineralization were significantly induced by CBP treatment. In addition, mRNA expression of ATF4 was intensely elevated in CBP-treated osteoblasts, indicating that the late-phase events of differentiation were promoted. We found that CBP activated the phosphorylation of JNK and extracellular signal-regulated kinase (ERK). Furthermore, pathway analyses using the various signaling pathway-specific inhibitors revealed that JNK activation, but not ERK activation, is essential for CBP-induced mineralization and ATF4 expression. Our results indicate that the JNK-mediated ATF4 pathway is required for CBP-promotive osteogenesis.