Maintenance of proper “labile iron” levels is a critical component in preserving homeostasis. Iron is a vital element that is a constituent of a number of important macromolecules, including those involved in energy production, respiration, DNA synthesis, and metabolism; however, excess “labile iron” is potentially detrimental to the cell or organism or both because of its propensity to participate in oxidation–reduction reactions that generate harmful free radicals. Because of this dual nature, elaborate systems tightly control the concentration of available iron. Perturbation of normal physiologic iron concentrations may be both a cause and a consequence of cellular damage and disease states. This review highlights the molecular mechanisms responsible for regulation of iron absorption, transport, and storage through the roles of key regulatory proteins, including ferroportin, hepcidin, ferritin, and frataxin. In addition, we present an overview of the relation between iron regulation and oxidative stress and we discuss the role of functional iron overload in the pathogenesis of hemochromatosis, neurodegeneration, and inflammation. Antioxid. Redox Signal. 10, 997–1030.

Clostridium butyricum MIYAIRI 588 (CBM 588) is a probiotic bacterium that has previously been used to prevent antibiotic-associated diarrhea. However, the underlying mechanism by which CBM 588 protects the gut epithelial barrier remains unclear. Here, we show that CBM 588 increased the abundance of Bifidobacterium, Lactobacillus, and Lactococcus species in the gut microbiome and also enhanced the intestinal barrier function of mice with antibiotic-induced dysbiosis. Additionally, CBM 588 significantly promoted the expansion of IL-17A-producing γδT cells and IL-17A-producing CD4 cells in the colonic lamina propria (cLP), which was closely associated with changes in the intestinal microbial composition. Additionally, CBM 588 plays an important role in controlling antibiotic-induced gut inflammation through upregulation of anti-inflammatory lipid metabolites such as palmitoleic acid, 15d-prostaglandin J2, and protectin D1. This study reveals a previously unrecognized mechanism of CBM 588 and provides new insights into gut epithelial barrier protection with probiotics under conditions of antibiotic-induced dysbiosis.

An effective utilization of intracellular iron is a prerequisite for erythroid differentiation and hemoglobinization. Ferritin, consisting of 24 subunits of H and L, plays a crucial role in iron homeostasis. Here, we have found that the H subunit of the ferritin gene is activated at the transcriptional level during hemin-induced differentiation of K562 human erythroleukemic cells. Transfection of various 5′ regions of the human ferritin H gene fused to a luciferase reporter into K562 cells demonstrated that hemin activates ferritin H transcription through an antioxidant-responsive element (ARE) that is responsible for induction of a battery of phase II detoxification genes by oxidative stress. Gel retardation and chromatin immunoprecipitation assays demonstrated that hemin induced binding of cJun, JunD, FosB, and Nrf2 b-zip transcription factors to AP1 motifs of the ferritin H ARE, despite no significant change in expression levels or nuclear localization of these transcription factors. A Gal4-luciferase reporter assay did not show activation of these b-zip transcription factors after hemin treatment; however, redox factor 1 (Ref-1), which increases DNA binding of Jun/Fos family members via reduction of a conserved cysteine in their DNA binding domains, showed induced nuclear translocation after hemin treatment in K562 cells. Consistently, Ref-1 enhanced Nrf2 binding to the ARE and ferritin H transcription. Hemin also activated ARE sequences of other phase II genes, such as GSTpi and NQO1. Collectively, these results suggest that hemin activates the transcription of the ferritin H gene during K562 erythroid differentiation by Ref-1-mediated activation of these b-zip transcription factors to the ARE.

Coordinated regulation of PI3-kinase (PI3K) and the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) plays a pivotal role in various cell functions. PTEN is deficient in many cancer cells, including Jurkat human leukemia. Here, we demonstrate that the status of PTEN determines cellular susceptibility to oxidative stress through antioxidant-responsive element (ARE)-mediated transcription of detoxification genes. We found that ferritin H transcription was robustly induced in tert-butylhydroquinone (t-BHQ)-treated Jurkat cells via an ARE, and it was due to PTEN deficiency. Chromatin immunoprecipitation assays revealed that p300/CREB-binding protein (CBP) histone acetyltransferases and Nrf2 recruitment to the ARE and Bach1 release were blocked by the PI3K inhibitor LY294002, along with the partial inhibition of Nrf2 nuclear accumulation. Furthermore, acetylations of histone H3 Lys9 and Lys18, and deacetylation of Lys14 were associated with the PI3K-dependent ARE activation. Consistently, PTEN restoration in Jurkat cells inhibited t-BHQ–mediated expression of ferritin H and another ARE-regulated gene NAD(P)H:quinone oxidoreductase 1. Conversely, PTEN knockdown in K562 cells enhanced the response to t-BHQ. The PTEN status under t-BHQ treatment affected hydrogen peroxide-mediated caspase-3 cleavage. The PI3K-dependent ferritin H induction was observed by treatment with other ARE-activating agents ethoxyquin and hemin. Collectively, the status of PTEN determines chromatin modifications leading to ARE activation.

Recent development of immunosuppressive therapy has provided a platform for clinical human leukocyte antigen (HLA)- and ABO-incompatible kidney transplantation. However, the prognosis seems to be different between the two. Accommodation, the condition of no injury even in the presence of antidonor antibody, is one of the key factors for successful transplantation with antidonor antibody. The purpose of this study was to compare signal transduction between anti-A/B and anti-HLA antibody reaction and to elucidate the mechanisms underlying accommodation. Blood type A- or B-transferase gene was transfected into human EA.hy926 endothelial cells. After cell sorting, A- or B-expressing cells at high levels were obtained. The effects of anti-HLA and anti-A/B antibody binding on complement-mediated cytotoxicity and signal transduction were examined. Preincubation with anti-HLA antibodies only at low levels (<10% of saturation level) or anti-A/B antibodies at high levels (even at near saturation levels) for 24 hr resulted in resistance to complement-mediated cytotoxicity. Anti-A/B antibody ligation inactivated ERK1/2 pathway and increased complement regulatory proteins such as CD55 and CD59, whereas anti-HLA ligation activated PI3K/AKT pathway and increased cytoprotective genes such as hemeoxygenase-1 and ferritin H. Complement inhibition by upregulation of CD55 and CD59 through ERK1/2 inactivation might play a substantial role in accommodation after ABO-incompatible transplantation, which could also explain the intriguing finding of C4d deposition in the graft without rejection.