Hereditary haemochromatosis (HH), which affects some 1 in 400 and has an estimated carrier frequency of 1 in 10 individuals of Northern European descent, results in multi-organ dysfunction caused by increased iron deposition, and is treatable if detected early. Using linkage-disequilibrium and full haplotype analysis, we have identified a 250-kilobase region more than 3 megabases telomeric of the major histocompatibility complex (MHC) that is identical-by-descent in 85% of patient chromosomes. Within this region, we have identified a gene related to the MHC class I family, termed HLA-H, containing two missense alterations. One of these is predicted to inactivate this class of proteins and was found homozygous in 83% of 178 patients. A role of this gene in haemochromatosis is supported by the frequency and nature of the major mutation and prior studies implicating MHC class I-like proteins in iron metabolism.

We recently reported the positional cloning of a candidate gene for hereditary hemochromatosis called HFE. The gene product, a member of the major histocompatibility complex class I-like family, was found to have a mutation, Cys-282 3 Tyr (C282Y), in 85% of patient chromosomes. This mutation eliminates the ability of HFE to associate with ␤ 2 -microglobulin (␤ 2 m) and prevents cellsurface expression. A second mutation that has no effect on ␤ 2 m association, H63D, was found in eight out of nine patients heterozygous for the C282Y mutant. In this report, we demonstrate in cultured 293 cells overexpressing wild-type or mutant HFE proteins that both the wild-type and H63D HFE proteins form stable complexes with the transferrin receptor (TfR). The C282Y mutation nearly completely prevents the association of the mutant HFE protein with the TfR. Studies on cell-associated transferrin at 37°C suggest that the overexpressed wild-type HFE protein decreases the affinity of the TfR for transferrin. The overexpressed H63D protein does not have this effect, providing the first direct evidence for a functional consequence of the H63D mutation. Addition of soluble wild-type HFE͞␤ 2 m heterodimers to cultured cells also decreased the apparent affinity of the TfR for its ligand under steady-state conditions, both in 293 cells and in HeLa cells. Furthermore, at 4°C, the added soluble complex of HFE͞␤ 2 m inhibited binding of transferrin to HeLa cell TfR in a concentration-dependent manner. Scatchard plots of these data indicate that the added heterodimer substantially reduced the affinity of TfR for transferrin. These results establish a molecular link between HFE and a key protein involved in iron transport, the TfR, and raise the possibility that alterations in this regulatory mechanism may play a role in the pathogenesis of hereditary hemochromatosis.

HFE is an MHC-related protein that is mutated in the iron-overload disease hereditary hemochromatosis. HFE binds to transferrin receptor (TfR) and reduces its affinity for iron-loaded transferrin, implicating HFE in iron metabolism. The 2.6 A crystal structure of HFE reveals the locations of hemochromatosis mutations and a patch of histidines that could be involved in pH-dependent interactions. We also demonstrate that soluble TfR and HFE bind tightly at the basic pH of the cell surface, but not at the acidic pH of intracellular vesicles. TfR:HFE stoichiometry (2:1) differs from TfR:transferrin stoichiometry (2:2), implying a different mode of binding for HFE and transferrin to TfR, consistent with our demonstration that HFE, transferrin, and TfR form a ternary complex.

During Drosophila neurogenesis, differential segregation of Numb is necessary for daughter cells of asymmetric divisions to adopt distinct fates, at least partly by biasing the Notch-mediated cell-cell interaction. We have isolated a highly conserved mammalian homolog of Drosophila numb, m-numb. During mouse cortical neurogenesis, m-Numb is asymmetrically localized to the apical membrane of dividing ventricular neural progenitors. Depending upon the orientation of the cleavage plane, m-Numb may be distributed into one or both of the daughter cells. When expressed in Drosophila embryos, m-Numb is localized asymmetrically in dividing neural precursors and rescues the numb mutant phenotype. Furthermore, m-Numb can physically interact with mouse Notch1. We propose that some shared molecular mechanisms, both cell-intrinsic and cell-extrinsic, generate asymmetric cell divisions during neurogenesis of vertebrates and invertebrates.

We recently reported the positional cloning of a candidate gene for hereditary hemochromatosis (HH), called HLA-H, which is a novel member of the major histocompatibility complex class I family. A mutation in this gene, cysteine 282 3 tyrosine (C282Y), was found to be present in 83% of HH patient DNAs, while a second variant, histidine 63 3 aspartate (H63D), was enriched in patients heterozygous for C282Y. The functional relevance of either mutation has not been described. Coimmunoprecipitation studies of cell lysates from human embryonic kidney cells transfected with wild-type or mutant HLA-H cDNA demonstrate that wild-type HLA-H binds ␤ 2 -microglobulin and that the C282Y mutation, but not the H63D mutation, completely abrogates this interaction. Immunofluorescence labeling and subcellular fractionations demonstrate that while the wild-type and H63D HLA-H proteins are expressed on the cell surface, the C282Y mutant protein is localized exclusively intracellularly. This report describes the first functional significance of the C282Y mutation by suggesting that an abnormality in protein trafficking and/or cell-surface expression of HLA-H leads to HH disease.Hereditary hemochromatosis (HH) 1 is an autosomal recessive disorder of iron metabolism and represents one of the most common inherited disorders in individuals of Northern European descent with an estimated carrier frequency between 1 in 8 and 1 in 10 (1, (2). In patients with HH, excessive iron deposition in a variety of organs leads to multi-organ dysfunction. Recently, we reported a mutation in a novel MHC class I-like gene, called HLA-H (3). Eighty-three percent of HH patient DNAs were found to be homozygous for this mutation, which consists of a single base transition of G to A and results in a change of cysteine 282 3 tyrosine (C282Y). Subsequent reports have confirmed the high frequency of this founder mutation in other HH patients (4 -6), providing further support that HLA-H is the primary HH locus. A second missense mutation, histidine 63 3 aspartate (H63D), was also reported that was enriched in heterozygotes with the C282Y mutation (eight of nine cases) (3). The specific role that either of these mutations in HLA-H play in the etiology of HH disease has not been elucidated.The HLA-H protein is similar to MHC class I family molecules including HLA-A2, nonclassical class I molecules such as HLA-G, and the human neonatal Fc receptor (FcRn). All four of the invariant cysteine residues that form disulfide bridges in the ␣ 2 and ␣ 3 domains of MHC class I family members are present in the HLA-H protein. One of these conserved cysteine residues is altered in the C282Y mutation. The integrity of the conserved disulfide linkages has been suggested to be critical for proper maintenance of the secondary and tertiary structure of the protein allowing interactions with accessory molecules such as ␤ 2 -microglobulin (7). Importantly, the functional significance of an interaction between ␤ 2 -microglobulin and an unknown class I-like molecule in HH disease was s...

Hereditary hemochromatosis (HH) is the most common autosomal recessive disorder known in humans. A candidate gene for HH called HFE has recently been cloned that encodes a novel member of the major histocompatibility complex class I family. Most HH patients are homozygous for a Cys-2823Tyr (C282Y) mutation in HFE gene, which has been shown to disrupt interaction with ␤ 2 -microglobulin; a second mutation, His-633Asp (H63D), is enriched in HH patients who are heterozygous for C282Y mutation. The aims of this study were to determine the effects of the C282Y and H63D mutations on the cellular trafficking and degradation of the HFE protein in transfected COS-7 cells. The results indicate that, while the wild-type and H63D HFE proteins associate with ␤ 2 -microglobulin and are expressed on the cell surface of COS-7 cells, these capabilities are lost by the C282Y HFE protein. We present biochemical and immunof luorescence data that indicate that the C282Y mutant protein: (i) is retained in the endoplasmic reticulum and middle Golgi compartment, (ii) fails to undergo late Golgi processing, and (iii) is subject to accelerated degradation. The block in intracellular transport, accelerated turnover, and failure of the C282Y protein to be presented normally on the cell surface provide a possible basis for impaired function of this mutant protein in HH.Hereditary hemochromatosis (HH) is a common autosomal recessive disorder characterized by iron overload of parenchymal cells in many organs including the liver, pancreas, heart, joints, and endocrine organs due to increased iron absorption in the gastrointestinal tract (1-4). Clinical consequences of iron accumulation in these organs include cirrhosis of the liver, hepatocellular carcinoma, diabetes, heart failure, arthritis, and hypogonadism. Within the Caucasian population, 1 in 300-400 individuals is homozygous and 1 in 8-10 individuals is heterozygous for HH (3,5). Recently, Feder et al. (6) reported that 83% of 178 American HH patients were homozygous for the same missense mutation (C282Y) in a novel major histocompatibility complex (MHC) class I-like gene, originally called HLA-H, but now designated HFE (7). [Although Feder et al. (6) originally designated the HH candidate gene HLA-H, this designation had already been assigned to a pseudogene and the HH locus had already been assigned the name HFE by the nomenclature committee (7).] Eight of nine patients with HH who were heterozygous for this mutation were found to have a different missense mutation (H63D) on the other HFE allele, although 17% of the normal population also carried one H63D allele. These findings were confirmed by Beutler et al. (8), who found that 82% of 147 HH patients were homozygous for the C282Y mutation and 10 were compound heterozygotes for C282Y and H63D alleles. Subsequent studies reported that 72-91% of French patients (9, 10), 64% of Italian patients (11), and 100% of Australian patients (12) were homozygous for the C282Y mutation. Independent support for HFE as the HH gene comes ...

The achaete-scute genes encode essential transcription factors in normal Drosophila and vertebrate nervous system development. Human achaete-scute homolog-1 (hASH1) is constitutively expressed in a human lung cancer with neuroendocrine (NE) features, small cell lung cancer (SCLC), and is essential for development of the normal pulmonary NE cells that most resemble this neoplasm. Mechanisms regulating achaete-scute homolog expression outside of Drosophila are presently unclear, either in the context of the developing nervous system or in normal or neoplastic cells with NE features. We now provide evidence that the protein hairy-enhancer-of-split-1 (HES-1) acts in a similar manner as its Drosophila homolog, hairy, to transcriptionally repress achaete-scute expression. HES-1 protein is detected at abundant levels in most non-NE human lung cancer cell lines which lack hASH1 but is virtually absent in hASH1-expressing lung cancer cells. Moreover, induction of HES-1 in a SCLC cell line down-regulates endogenous hASH1 gene expression. The repressive effect of HES-1 is directly mediated by binding of the protein to a class C site in the hASH1 promoter. Thus, a key part of the process that determines neural fate in Drosophila is conserved in human lung cancer cells. Furthermore, modulation of this pathway may underlie the constitutive hASH1 expression seen in NE tumors such as SCLC, the most virulent human lung cancer.Basic helix-loop-helix transcription factors homologous to the Drosophila achaete-scute complex (AS-C) are critical to nervous system development in multiple organisms (1-9). Specifically, mouse transgenic knockout studies indicate that transient expression of achaete-scute homolog-1 (termed MASH1) in neural precursor cells is necessary for establishment of a subset of autonomic, olfactory, and enteric neurons, and adrenal chromaffin cells (1, 6). Recently, we have shown that human achaete-scute homolog-1 (hASH1) is constitutively expressed in an important tumor, small cell lung cancer (SCLC) (10), which accounts for 25% of over 150,000 new cases of lung cancer each year. In this extremely virulent and metastatic cancer where the 5-year survival is less than 5%, hASH1 expression appears tightly linked to the neuroendocrine (NE) properties that characterize SCLC (11-13). The possibility that this transcription factor could be integral to the process of NE differentiation is underscored by our recent finding that pulmonary NE cells, the normal bronchial cells that most resemble the SCLC phenotype, fail to develop in transgenic mice homozygous for MASH1 deletion (13). Furthermore, depletion of hASH1 in classic SCLC lines results in a significant reduction of NE marker expression (13). These data indicate that delineating the molecular events which lead to constitutive hASH1 expression may prove essential for understanding the establishment of the NE phenotype in SCLC.

SGLT2 (for “Sodium GLucose coTransporter” protein 2) is the major protein responsible for glucose reabsorption in the kidney and its inhibition has been the focus of drug discovery efforts to treat type 2 diabetes. In order to better clarify the human tissue distribution of expression of SGLT2 and related members of this cotransporter class, we performed TaqMan™ (Applied Biosystems, Foster City, CA, USA) quantitative polymerase chain reaction (PCR) analysis of SGLT2 and other sodium/glucose transporter genes on RNAs from 72 normal tissues from three different individuals. We consistently observe that SGLT2 is highly kidney specific while SGLT5 is highly kidney abundant; SGLT1, sodium-dependent amino acid transporter (SAAT1), and SGLT4 are highly abundant in small intestine and skeletal muscle; SGLT6 is expressed in the central nervous system; and sodium myoinositol cotransporter is ubiquitously expressed across all human tissues.Electronic Supplementary MaterialSupplementary material is available for this article at 10.1007/s13300-010-0006-4 and is accessible for authorized users.