Intronic SNP rs3811647 of the human transferrin gene modulates its expression in hepatoma cells (original) (raw)
Related papers
2012
Introducción: La transferrina (Tf) ejerce una función crucial en el mantenimiento de la homeostasis sistémica del hierro. La expresión del gen de la transferrina es controlada a nivel transcripcional, aunque la posible influencia de factores genéticos todavía se desconoce. Objetivo: Estudiar el papel del rs3811647 en la expresión de la transferrina mediante un ensayo in-vitro en células de hepatoma. Diseño y métodos: Células Hep3B fueron co-transfectadas con vectores que contenían las variantes A (VarA-Tfluc) y G (VarG-Tf-luc) del rs3811647, utilizandose la luciferasa como marcador de la expresión del gen Tf. Resultados: Los ensayos con la luciferasa mostraron un mayor aumento de la expresión del gen Tf en presencia de la variante A comparada con la G (p < 0,05). El análisis in silico del SNP rs3811647 mostró que la presencia del alelo A puede constituir un sitio de unión del receptor de glucocorticoides (GR). Conclusión: El alelo A del SNP rs3811647 incrementa la expresión del gen Tf de modo que podría modular la variación interindividual en los niveles de transferrina sérica observados en diferentes poblaciones.
The Journal of biological chemistry, 1991
We present a comparative study of the cis- and trans-acting elements governing the expression of the human transferrin (Tf) gene in two tissues, liver and testis, where Tf is expressed at various levels. We have previously identified the elements of the promoter, negative, and enhancer regions involved in the liver-specific expression of the gene. By transfection experiments of primary cultured rat Sertoli cells compared with hepatoma cells, DNase I footprinting, and gel retardation studies, we have analyzed 3.6 kilobase pairs of the Tf regulatory region. The far upstream enhancer functional in Hep3B cells is inactive in Sertoli cells; in the two cell types, different nuclear factors appear to bind to a DNA domain crucial for enhancer activity. Similar negative- and positive-acting elements are present in the distal promoter in both tissues. However different combinations of proximal promoter elements control tissue-specific expression. Liver-specific transcription is governed by th...
Stoichiometries of transferrin receptors 1 and 2 in human liver
Blood Cells, Molecules, and Diseases, 2010
Mutations in either the hereditary hemochromatosis protein, HFE, or transferrin receptor 2, TfR2, result in a similarly severe form of the most common type of iron overload disease called hereditary hemochromatosis. Models of the interactions between HFE, TfR1, and TfR2 imply that these proteins are present in different molar concentrations in the liver, where they control expression of the iron regulatory hormone, hepcidin, in response to body iron loading. The aim of this study was to determine in vivo levels of mRNA by quantitative RT-PCR and concentrations of these proteins by quantitative immunoblotting in human liver tissues. The level of TfR2 mRNA was 21-and 63-fold higher than that of TfR1 and HFE, respectively. Molar concentration of TfR2 protein was the highest and determined to be 1.95 nmoles/g protein in whole cell lysates and 10.89 nmoles/g protein in microsomal membranes. Molar concentration of TfR1 protein was 4.5-and 6.1-fold lower than that of TfR2 in whole cell lysates and membranes, respectively. The level of HFE protein was below 0.53 nmoles/g of total protein. HFE is thus present in substoichiometric concentrations with respect to both TfR1 and TfR2 in human liver tissue. This finding supports a model, in which availability of HFE is limiting for formation of complexes with TfR1 or TfR2.
Gene, 1986
Transferrin is a major plasma protein that transports iron to proliferating cells throughout the body. A clone containing the 5' region of the human transferrin gene has been isolated and characterized. A 14 kb EcoRI fragment was identified that contained the first 8 exons of the transfer+ gene and 3.6 kb of its 5' flanking region. Conserved sequences identical or homologous to regulatory elements responding to heavy metals, glucocorticoid receptor and a putative acute phase reaction signal were identified in the 5' flanking region and intron 1. Also, the regulatory region of the transferrin gene contains a 14-bp sequence which closely matches sequences found in the interleukin-2 and y-interferon genes. All three genes are expressed by T lymphocytes before proliferation. A secondary loop structure similar to that proposed for the ovotransferrin gene can be formed by sequences in the 5' untranslated region of the transferrin mRNA.
The Journal of biological chemistry, 1993
We have previously identified the functional regions involved in the regulation of human transferrin (Tf) gene expression in the liver and in Sertoli cells of the testis. Here, we show that a different cellular distribution of transcription factors, interacting with the same proximal promoter regions (PRI and PRII), modulates cell type-specific transcription. In the liver, hepatocyte nuclear factor 4 (HNF-4) and the chicken ovalbumin upstream promoter transcription factor (COUP-TF) act at the PRI site, while CCAAT/enhancer-binding proteins (C/EBPs) act at the PRII site. In the testis, distinct combinations of Sertoli proteins SP-A and SP-D and COUP-TF bind to the PRI site, while SP-alpha and SP-beta bind to the PRII site. Cotransfection experiments in Hep3B cells revealed that mostly HNF-4, C/EBP-alpha, C/EBP-delta, and, to a lesser extent, COUP-TF stimulated transcription driven by the -125/+39 region. In Sertoli cells, HNF-4 and COUP-TF appeared to repress, while the C/EBP factors...
Virchows Archiv B Cell …, 1988
The expression of transferrin receptors (TfR's) has been investigated in eight liver biopsy specimens (four from patients without demonstrable iron and four from patients with iron storage due to primary hemochromatosis (HC)) using immunoelectron microscopy to demonstrate TfR's by the simultaneous application of two specific monoclonal antibodies (OKT9 and B3/25) to tissue chopper sections. In the four specimens without iron overload, hepatocytes, but not sinusoidal lining cells, stained positively and immunoreactivity was mainly localized in the cytoplasm. Positively stained cisternae of the endoplasmic reticulum indicated synthesis of the TfR. The presence of TfR's on segments and coated invaginations of the sinusoidal membrane and in small, but otherwise unidentified vesicles in the cytoplasm is compatible with endo-/exocytotic transport and recycling of TfR's as demonstrated by biochemical studies. Occasional positively stained material in canalicular lumina together with positively stained canalicular microvilli and pericanalicular vesicles suggest that transcellular transport may be an additional pathway for TfR's. In three biopsies showing severe iron overload due to HC, TfR immunoreactivity was completely absent. The remaining specimen showing HC, exhibited relatively mild iron overload and showed only a few positively stained hepatocytes. This supports the previously reported disappearance of hepatic TfR expression in HC when iron overload is severe.
Targeted Disruption of the Hepatic Transferrin Receptor 2 Gene in Mice Leads to Iron Overload
Gastroenterology, 2007
Transferrin receptor 2 (TfR2) plays a key role in the regulation of iron metabolism. Mutations of TfR2 in humans cause type 3 hereditary hemochromatosis. Although highly expressed in liver, several studies have reported TfR2 expression in other tissues. To determine the contribution of liver expressed TfR2 in iron homeostasis, we have generated and characterized a liver-specific TfR2-knockout (KO) mouse. Methods: Liver-specific TfR2-KO mice were generated by crossing TfR2-floxed mice with transgenic albumin-Cre mice. Tissue and serum from homozygous TfR2-floxed mice with and without albumin-Cre were analyzed. Serum transferrin saturation, hepatic, and splenic iron concentrations were determined. The expression of iron-related mRNA transcripts was analyzed by real-time PCR. Levels of the iron-related proteins TfR1, TfR2, ferritin, and prohepcidin were analyzed by immunoblotting. Results: Liver-specific TfR2-KO mice develop significant iron overload comparable to complete TfR2-KO mice. At all ages studied, transferrin saturation, hepatic iron concentration, and hepatic ferritin were significantly elevated. Hepatic TfR2 mRNA and protein were absent in the livers of liver-specific TfR2-KO mice, and TfR1 expression was reduced consistent with liver iron loading. At 5 weeks of age, hepcidin1 mRNA, and prohepcidin protein were decreased in liver-specific TfR2-KO compared to control mice. Conclusions: The significant iron loading and modulation of expression of iron-related genes in liver-specific TfR2-KO mice demonstrates that the liver is the primary site for TfR2 expression and activity and that liver-expressed TfR2 is required for the regulation of hepcidin1.