apoB and apobec1, two genes key to lipid metabolism, are transcriptionally regulated by p53.

p53 is an established tumor suppressor gene activating the transcription of multiple target genes. Apolipoprotein B (apo B), a dietary lipid transporter, occurs as apo B-100 and apoB-48, created by a premature stop codon by apo B mRNA-editing enzyme complex 1 (apobec1). We have identified p53 response elements (p53RE) in the genes encoding for apoB and apobec1, cloned these novel p53RE and by performing functionality, chromatin immunoprecipitation (ChIP) and expression assays in cancer cell lines, confirmed that these genes are transcriptionally regulated by p53. In C57bl/6 mice treated with adriamycin, a potent p53 inducer, intestinal/liver mRNA expression of apoB and apobec1 and liver apoB editing levels were elevated. In irradiated wild type C57bl6 mice but not p53 knockout mice, liver and intestine apoB but not apobec1 mRNA expression was elevated. In this work, we have identified that p53 regulates the transcription of two central lipid metabolism players. We further show, for the first time, an involvement of p53 in the RNA editing process, through the transcription of apobec1. Our findings may reveal a previously unknown role for p53 in the direct regulation of atherogenic lipoproteins and a possible role for these genes in classical p53 activities.

Hepcidin in acute iron toxicity.

BACKGROUND: Hepcidin regulates extracellular iron concentration by inhibiting iron release from macrophages and preventing iron absorption in the intestine. Our objective was to evaluate the expression of hepcidin in the liver in acute iron poisoning in a rat model. METHODS: Male Wistar rats were assigned to group 1, who received 750 mg/kg elemental iron (LD(50)) by gavage, and group 2 (control), who received distilled water. Iron concentrations and liver transaminases were measured in the serum. Hepcidin messenger RNA levels were measured in the liver. RESULTS: Mean serum iron levels, aspartate aminotransferase, alanine aminotransferase, and uric acid were significantly higher in group 1 compared to group 2 (P < .0001, P = .01, P < .0001, and P = 0.0001, respectively). Hepcidin messenger RNA levels in the liver were significantly higher in the study group (P = .005). CONCLUSIONS: In acute iron intoxication, hepcidin expression in the liver significantly increased. Further studies are needed to determine whether hepcidin levels correlate with the severity of the intoxication.

Hepcidin, a key regulator of iron metabolism, is transcriptionally activated by p53.

Hepcidin is an iron-regulatory protein that is upregulated in response to increased iron or inflammatory stimuli. Hepcidin reduces serum iron and induces iron sequestration in the reticuloendothelial macrophages - the hallmark of anaemia of inflammation. Iron deprivation is used as a defense mechanism against infection, and it also has a beneficial effect on the control of cancer. The tumour-suppressor p53 transcriptionally regulates genes involved in growth arrest, apoptosis and DNA repair, and perturbation of p53 pathways is a hallmark of the majority of human cancers. This study inspected a role of p53 in the transcriptional regulation of hepcidin. Based on preliminary bioinformatics analysis, we identified a putative p53 response-element (p53RE) contained in the hepcidin gene (HAMP) promoter. Chromatin immunoprecipitation (ChIP), reporter assays and a temperature sensitive p53 cell-line system were used to demonstrate p53 binding and activation of the hepcidin promoter. p53 bound to hepcidin p53RE in vivo, andthis p53RE could confer p53-dependent transcriptional activation. Activation of p53 increased hepcidin expression, while silencing of p53 resulted in decreased hepcidin expression in human hepatoma cells. Taken together, these results define HAMP as a novel transcriptional target of p53. We hypothesise that hepcidin upregulation by p53 is part of a defence mechanism against cancer, through iron deprivation. Hepcidin induction by p53 might be involved in the pathogenesis of anaemia accompanying cancer.

Downregulation of hepcidin and haemojuvelin expression in the hepatocyte cell-line HepG2 induced by thalassaemic sera.

Beta-thalassaemia represents a group of diseases, in which ineffective erythropoiesis is accompanied by iron overload. In a mouse model of beta-thalassaemia, we observed that the liver expressed relatively low levels of hepcidin, which is a key factor in the regulation of iron absorption by the gut and of iron recycling by the reticuloendothelial system. It was hypothesised that, despite the overt iron overload, a putative plasma factor found in beta-thalassaemia might suppress liver hepcidin expression. Sera from beta-thalassaemia and haemochromatosis (C282Y mutation) patients were compared with those of healthy individuals regarding their capacity to induce changes the expression of key genes of iron metabolism in human HepG2 hepatoma cells. Sera from beta-thalassaemia major patients induced a major decrease in hepcidin (HAMP) and lipocalin2 (oncogene 24p3) (LCN2) expression, as well as a moderate decrease in haemojuvelin (HFE2) expression, compared with sera from healthy individuals. A significant correlation was found between the degree of downregulation of HAMP and HFE2 induced by beta-thalassaemia major sera (r = 0.852, P < 0.0009). Decreased HAMP expression was also found in HepG2 cells treated with sera from beta-thalassaemia intermedia patients. In contrast, the majority of sera from hereditary haemochromatosis patients induced an increase in HAMP expression, which correlated with transferrin (Tf) saturation (r = 0.765, P < 0.0099). Our results suggest that, in beta-thalassaemia, serum factors might override the potential effect of iron overload on HAMP expression, thereby providing an explanation for the failure to arrest excessive intestinal iron absorption in these patients.

mRNA expression of iron regulatory genes in beta-thalassemia intermedia and beta-thalassemia major mouse models.

beta-Thalassemia is an inherited anemia in which synthesis of the hemoglobin beta-chain is decreased. The excess unmatched alpha-globin chains accumulate in the growing erythroid precursors, causing their premature death (ineffective erythropoiesis). Clinical features of beta-thalassemia include variably severe anemia and iron accumulation due to increased intestinal iron absorption. The most anemic patients require regular blood transfusions, which exacerbate their iron overload and result in damage to vital organs. The hepatic peptide hepcidin, a key regulator of iron metabolism in mammals, was recently found to be low in the urine of beta-thalassemia patients, compared with healthy controls, despite their iron overload. In our work, we measured by RQ-PCR the liver mRNA expression of hepcidin and other iron regulatory genes in beta-thalassemia major mouse model (C57Bl/6 Hbb(th3/th3)), and compared it with beta-thalassemia intermedia mouse model (C57Bl/6 Hbb(th3/+)) and control mice. We found decreased expression of hepcidin and TfR2 and increased expression of TfR1 and NGAL in the beta-thalassemia mouse models, compared with the control mice. Significant down-regulation of hepcidin expression in beta-thalassemia major, despite iron overload, might explain the increased iron absorption typically observed in thalassemia.

Role of iron in inducing oxidative stress in thalassemia: Can it be prevented by inhibition of absorption and by antioxidants?

The pathophysiology of thalassemia is, to a certain extent, associated with the generation of labile iron in the pathological red blood cell (RBC). The appearance of such forms of iron at the inner and outer cell surfaces exposes the cell to conditions whereby the labile metal promotes the formation of reactive oxygen species (ROS) leading to cumulative cell damage. Another source of iron accumulation results from increased absorption due to decreased expression of hepcidin. The presence of labile plasma iron (LPI) was carried out using fluorescent probes in the FACS. RNA expression of hepcidin was measured in two models of thalassemic mice. Hepcidin expression was also measured in human hepatoma HepG2 cells following incubation with thalassemic sera. LPI was identified and could be quantitatively measured and correlated with other parameters of iron overload. Hepcidin expression was downregulated in the livers of thalassemic mice, in major more than in intermedia. Thalassemic sera down regulated hepcidin expression in HepG2 liver cells. A possible way to decrease iron absorption could be by modulating hepcidin expression pharmacologically, by gene therapy or by its administration. Treatment with combination of antioxidants such as N-acetylcysteine for proteins and vitamin E for lipids in addition to iron chelators could neutralize the deleterious effects of ROS and monitored by quantitation of LPI.

Exploring the role of hepcidin, an antimicrobial and iron regulatory peptide, in increased iron absorption in beta-thalassemia.

To develop new treatments for beta-thalassemia, it is essential to identify the genes involved in the relevant pathophysiological processes. Iron metabolism in thalassemia mice being investigated, focusing on the expression of a gene called hepcidin (Hamp), which is expressed in the liver and whose product (Hamp) is secreted into the bloodstream. In mice, iron overload leads to overexpression of Hamp, while Hamp-knockout mice suffer from hemochromatosis. The aim of this study is to investigate Hamp in the mouse model of beta-thalassemia and to address the potential gene transfer of Hamp to prevent abnormal iron absorption.