A role of SMAD4 in iron metabolism through the positive regulation of hepcidin expression

Genetics of Development and Disease Branch, 10/9N105, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Cell Metabolism (Impact Factor: 16.75). 01/2006; 2(6):399-409. DOI: 10.1016/j.cmet.2005.10.010
Source: PubMed

ABSTRACT Hereditary hemochromatosis, characterized by iron overload in multiple organs, is one of the most common genetic disorders among Caucasians. Hepcidin, which is synthesized in the liver, plays important roles in iron overload syndromes. Here, we show that a Cre-loxP-mediated liver-specific disruption of SMAD4 results in markedly decreased hepcidin expression and accumulation of iron in many organs, which is most pronounced in liver, kidney, and pancreas. Transcript levels of genes involved in intestinal iron absorption, including Dcytb, DMT1, and ferroportin, are significantly elevated in the absence of hepcidin. We demonstrate that ectopic overexpression of SMAD4 activates the hepcidin promoter and is associated with epigenetic modification of histone H3 to a transcriptionally active form. Moreover, transcriptional activation of hepcidin is abrogated in SMAD4-deficient hepatocytes in response to iron overload, TGF-beta, BMP, or IL-6. Our study uncovers a novel role of TGF-beta/SMAD4 in regulating hepcidin expression and thus intestinal iron transport and iron homeostasis.

  • Source
    • "In particular, post-translational modification of Histone H3, one of the core proteins of the nucleosome, regulates transcription and chromatin condensation [48]. Transfection of Smad4 into Smad4-null hepatocytes increases binding of Histone 3 acetylated at lysine 9 (H3K9) to the Hepcidin promoter [4]. Histone acetylation also appears to affect Stat3 binding to the Hepcidin promoter. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Hepcidin, a peptide hormone produced in the liver, decreases intestinal iron absorption and macrophage iron release via effects on ferroportin. Bone morphogenic protein and Stat3 signaling regulate Hepcidin's transcription. Hepcidin is a potential drug target for patients with iron overload syndromes because its levels are inappropriately low in these individuals. To generate a tool for identifying small molecules that modulate Hepcidin expression, we stably transfected human hepatocytes (HepG2) cells with a reporter construct containing 2.7 kb of the human Hepcidin promoter upstream of a firefly reporter gene. We used high throughput methods to screen 10,169 chemicals in duplicate for their effect on Hepcidin expression and cell viability. Regulators were identified as chemicals that caused a change > 3 standard deviations above or > 1 standard deviation below the mean of the other chemicals (z-score > 3 or < 1), while not adversely affecting cell viability, quantified by fluorescence assay. Following validation assays, we identified 16 chemicals in a broad range of functional classes that promote Hepcidin expression. All of the chemicals identified increased expression of bone morphogenic protein-dependent and/or Stat3-dependent genes, however none of them strongly increased phosphorylation of Smad1,5,8 or Stat3.
    Blood Cells Molecules and Diseases 12/2014; 53(4). DOI:10.1016/j.bcmd.2014.06.002 · 2.33 Impact Factor
  • Source
    • "This pathway can be activated by other cytokines including IL22 and Oncostatin-M which also increase hepcidin transcription, (Chung et al., 2010; Armitage et al., 2011). This inflammatory signaling relies on the BMPs/SMAD pathway to trigger hepcidin expression; in fact SMAD4-KO mice do not respond to the stimulation of IL6 (Wang et al., 2005). Activin-B, which belongs to the TGF-beta family, was shown to be stimulated by inflammation and to induce hepcidin via the BMP/SMAD pathway, thus it may cooperate and enhance the IL6-dependent stimulation and it could represent a connecting component between iron status and inflammation (Besson-Fournier et al., 2012; Figure 2B). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The discovery of hepcidin clarified the basic mechanism of the control of systemic iron homeostasis. Hepcidin is mainly produced by the liver as a propeptide and processed by furin into the mature active peptide. Hepcidin binds ferroportin, the only cellular iron exporter, causing the internalization and degradation of both. Thus hepcidin blocks iron export from the key cells for dietary iron absorption (enterocytes), recycling of hemoglobin iron (the macrophages) and the release of storage iron from hepatocytes, resulting in the reduction of systemic iron availability. The BMP/HJV/SMAD pathway is the major regulator of hepcidin expression that responds to iron status. Also inflammation stimulates hepcidin via the IL6/STAT3 pathway with a support of an active BMP/HJV/SMAD pathway. In some pathological conditions hepcidin level is inadequately elevated and reduces iron availability in the body, resulting in anemia. These conditions occur in the genetic iron refractory iron deficiency anemia and the common anemia of chronic disease (ACD) or anemia of inflammation. Currently, there is no definite treatment for ACD. Erythropoiesis-stimulating agents and intravenous iron have been proposed in some cases but they are scarcely effective and may have adverse effects. Alternative approaches aimed to a pharmacological control of hepcidin expression have been attempted, targeting different regulatory steps. They include hepcidin sequestering agents (antibodies, anticalins, and aptamers), inhibitors of BMP/SMAD or of IL6/STAT3 pathway or of hepcidin transduction (siRNA/shRNA) or ferroportin stabilizers. In this review we summarized the biochemical interactions of the proteins involved in the BMP/HJV/SMAD pathway and its natural inhibitors, the murine and rat models with high hepcidin levels currently available and finally the progresses in the development of hepcidin antagonists, with particular attention to the role of heparins and heparin sulfate proteoglycans in hepcidin expression and modulation of the BMP6/SMAD pathway.
    Frontiers in Pharmacology 04/2014; 5:86. DOI:10.3389/fphar.2014.00086 · 3.80 Impact Factor
  • Source
    • "Recent findings indicate that HFE-dependent signals function together with signals induced by the binding of bone morphogenetic proteins (BMPs) to the BMP receptor and the coreceptor hemojuvelin (HJV) (Andriopoulos et al 2009; Babitt et al 2006; Meynard et al 2009). These signals lead to activation of the SMAD4 (similar to mothers against decapentaplegic 4) transcription factor, which acts directly on the hepcidin promoter (Wang et al 2005). Pro-inflammatory cytokines, including interleukin-6 (IL-6), tumor necrosis factor α (TNFα) and IL-1, constitute another important stimulus for the transcriptional upregulation of hepcidin (Lee et al 2004; Lee et al 2005; Nemeth et al 2004a). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of iron on immune function has been long appreciated. However, the molecular basis for this interaction is less well understood. Recently, there have been several important advances that have shed light on the mechanisms that regulate mammalian iron metabolism. The new insights provide a conceptual framework for understanding and manipulating the cross-talk between iron homeostasis and the immune system. This article will review what is currently known about how disturbances of iron metabolism can affect immunity and how activation of the immune system can lead to alterations in iron balance.
    Archivum Immunologiae et Therapiae Experimentalis 09/2010; 58(6):407-15. DOI:10.1007/s00005-010-0095-9 · 2.82 Impact Factor
Show more