Biomedical subjects

T Langmann

Publications and source records attributed to T Langmann.

At least 19 recordsLinked to original sources

PubMed2006

Metabolic learning in the intestine: adaptation to nutrition and luminal factors.

There is increasing evidence that the magnitude and potential of intestinal nutrient absorption (sugars, fatty acids, cholesterol and triglycerides) and intestinal defense function are regulated by metabolic learning phenomena, and are influenced by dietary energy content and exercise. Metabolic overload syndromes, mainly obesity, and chronic malabsorption disorders such as inflammatory bowel disease and celiac disease have been defined as extreme phenotypes. Metabolic learning processes depend on developmental and transcriptional control systems of intestinal epithelial cell differentiation. The physiological differentiation zone of enterocytes is linked to the beta-catenin system, apolipoprotein apoA-IV and the master transcription factors Cdx2, HNF1alpha, and GATA4. In addition to these developmental regulatory transcription factors, nuclear receptors including RXR, LXR, PPAR, PXR, and CAR have been implicated in the generation of more absorptive enterocytes with a more differentiated phenotype on the one hand, and dedifferentiated cells with reduced capacity of detoxification and defense causing loss of junction control and barrier defects on the other. Large-scale analysis of gene expression profiles and identification of key pathways and master regulatory transcription factors will help dissect the role of nutritional and environmental factors as well as pharmacological intervention on mucosal homeostasis and disease, with potential applications for diagnosis and therapy.

Adaptation, Physiological↗

PubMed2002

Identification of regulatory elements in the human adipose most abundant gene transcript-1 ( apM-1) promoter: role of SP1/SP3 and TNF-alpha as regulatory pathways.

AIMS/HYPOTHESIS: The human adipocyte-specific apM-1 (adipose most abundant gene transcript-1) gene encodes for a secretory protein of the adipose tissue that seems to play a role in the pathogenesis of obesity-related insulin resistance and its expression is inhibited by TNF-alpha. Our aim was to characterize the tissue-specific regulation of the recently cloned apM-1 promoter and the mechanisms of TNF-alpha-induced downregulation of the apM-1 gene. METHODS: We characterised the apM-1 gene by electrophoretic mobility shift assays (EMSA) and luciferase reporter gene assays (LRA). RESULTS: Although several putative binding sites for transcription factors known to be involved in adipogenesis such as C/EBP and PPARgamma are present in the promoter, we could not detect any binding of these nuclear proteins from differentiated adipocytes. However, a proximal SP1 binding site specifically binds both, recombinant SP1 protein and SP1 derived from adipocyte nuclear extracts. Since the expression of SP1 during adipocyte differentiation has not yet been analysed, we could show by using EMSA, that binding activity of SP1 is increased during adipocyte differentiation. The stimulatory activity of SP1 was confirmed in LRA by cotransfection experiments in S2 Schneider cells lacking endogenous SP factors. An inhibitory activity of SP3 on the stimulatory effect of SP1 could be confirmed in LRA by contransfection experiments in adipocytes. Nuclear extracts from adipocytes incubated with TNF-alpha showed a reduced binding activity of SP1. CONCLUSION/INTERPRETATION: SP1 is expressed and its binding activity is enhanced during adipocyte differentiation. SP1 has stimulatory effects, SP3 has inhibitory effects on apM-1 promoter activity, mediated by a proximal SP1 binding site. The mechanism of TNF-alpha-induced inhibition of apM-1 gene expression is, at least in part, due to a decrease of transcriptional SP1 binding activity caused by TNF-alpha and thus provides a new mechanism of TNF-alpha-dependent signalling.

3T3 Cells↗

PubMed2001

Characterization of the ATPase cycle of human ABCA1: implications for its function as a regulator rather than an active transporter.

ABCA1 plays a key role in cellular cholesterol and phospholipid traffic. To explore the biochemical properties of this membrane protein we applied a Baculovirus-insect cell expression system. We found that human ABCA1 in isolated membranes showed a specific, Mg(2+)-dependent ATP binding but had no measurable ATPase activity. Nevertheless, conformational changes in ABCA1 could be demonstrated by nucleotide occlusion, even without arresting the catalytic cycle by phosphate-mimicking anions. Addition of potential lipid substrates or lipid acceptors (apolipoprotein A-I) did not modify the ATPase activity or nucleotide occlusion by ABCA1. Our data indicate that ATP hydrolysis by ABCA1 occurs at a very low rate, suggesting that ABCA1 may not function as an effective active transporter as previously assumed. In the light of the observed conformational changes we propose a regulatory function for human ABCA1.

ATP Binding Cassette Transporter 1↗

PubMed2001

ABCA6, a novel a subclass ABC transporter.

Here we report the cDNA cloning of a novel member of the ABC A transporter subfamily from human macrophages. The identified coding sequence is of 5.0 kb size and contains an open reading frame which encodes a 1617 amino acid polypeptide. Structurally, the putative ABC transporter protein product consists of two tandemly oriented subunits, each composed of a transmembrane domain followed by a nucleotide binding fold, and thus conforms to the group of full-size ABC transporters. We also demonstrate the existence of an alternative transcript that codes for a 637 amino acid protein variant bearing the features of a truncated half-size transporter. Among the human ABC transporter subfamily A the novel transporter shows highest protein sequence homology with ABCA8 (60%), followed by ABCA2 (32%) and ABCA1 (32%), respectively. In agreement with the proposed classification, the novel transporter was designated ABCA6. The ABCA6 gene is ubiquitously expressed with highest mRNA levels in liver, lung, heart and brain. Analysis of the genomic organization demonstrated that the ABCA6 gene is composed of 38 exons which extend across a region of 62 kb size on chromosome 17q24.2. Based on its structural features and its cholesterol-responsive regulation ABCA6 is potentially involved in macrophage lipid homeostasis.

ATP Binding Cassette Transporter 1↗

PubMed2001

The zinc finger protein 202 (ZNF202) is a transcriptional repressor of ATP binding cassette transporter A1 (ABCA1) and ABCG1 gene expression and a modulator of cellular lipid efflux.

The zinc finger gene 202 (ZNF202) located within a hypoalphalipoproteinemia susceptibility locus on chromosome 11q23 is a transcriptional repressor of various genes involved in lipid metabolism. To provide further evidence for a functional linkage between ZNF202 and hypoalphalipoproteinemia, we investigated the effect of ZNF202 expression on ATP binding cassette transporter A1 (ABCA1) and ABCG1. ABCA1 is a key regulator of the plasma high density lipoprotein pool size, whereas ABCG1 is another mediator of cellular cholesterol and phospholipid efflux in human macrophage. We demonstrate here that the full-length ZNF202m1 isoform binds to GnT repeats within the promotors of ABCA1 (-229/-210) and ABCG1 (-572/-552). ZNF202m1 expression in HepG2 cells dose-dependently repressed the promotor activities of ABCA1 and ABCG1. This transcriptional effect required the presence of the SCAN domain in ZNF202 and the functional integrity of a TATA box at position -24 of ABCA1, whereas the presence of GnT binding motifs was nonessential. The state of ZNF202 SCAN domain oligomerization affected the ability of the adjacent ZNF202 Krüppel-associated box domain to recruit the transcriptional corepressor KAP1. Overexpression of ZNF202m1 in RAW264.7 macrophages prevented the induction of ABCA1 gene expression by 20(S)OH-cholesterol and 9-cis-retinoic acid, further substantiating the interference of ZNF202 in critical elements of transcriptional activation. Finally, HDL and apoAImediated lipid efflux was significantly reduced in RAW264.7 cells stably expressing ZNF202m1. In conclusion, we have identified ABCA1 and ABCG1 as target genes for ZNF202-mediated repression and thus, provide evidence for a functional linkage between ZNF202 and hypoalphalipoproteinemia.

ATP Binding Cassette Transporter 1↗

PubMed2001

Structure, function and regulation of the ABC1 gene product.

The role of the ATP-binding cassette transporter 1 (ABCA1) in cellular lipid efflux and high density lipoprotein metabolism has been recently documented by mutations in genetic HDL deficiency syndromes such as classical Tangier disease. Analysis of ABCA1 knockout mice and overexpression studies have established the importance of ABCA1 as a major determinant of HDL cholesterol in plasma. These studies also indicate that ABCA1 is critically involved in cellular trafficking of cholesterol and choline-phospholipids and in total body lipid homeostasis, such as intestinal cholesterol and fat-soluble vitamin absorption and in the modulation of steroidogenesis. First insights into the upregulation of ABCA1 gene expression by cellular cholesterol and cAMP have identified critical ABCA1 promoter elements, which bind the transcription factors liver X receptor, retinoid X receptor, Sp1 and E-box proteins. The finding that a lipid sensitive subgroup of ABC transporters is able to translocate cholesterol and phospholipids supports the concept that in ABCA1 deficiency, compensatory mechanisms possibly involving MDR1, MDR3 and MRP-family members could be active. This suggests that a network of ABC transporters involved in cellular lipid transport exists, which is under the tight control of energy pathways directly linked to high density lipoprotein metabolism and atherogenesis.

ATP Binding Cassette Transporter 1↗

PubMed2001

Role of ABCG1 and other ABCG family members in lipid metabolism.

The molecular cloning and identification of mutations in ATP-binding cassette transporters in hereditary diseases have greatly expanded our knowledge of the normal physiology of intracellular lipid transport processes. In addition to the well-known ATP-binding cassette transporter A1 (ABCA1) molecule, ABC transporters belonging to the ABCG (White) subfamily (ABCG1, ABCG5, and ABCG8) have been shown to be critically involved in the regulation of lipid-trafficking mechanisms in macrophages, hepatocytes, and intestinal mucosa cells. ABCG1, the product of a sterol-induced gene, participates in cholesterol and phospholipid efflux. The ABCG5 and ABCG8 transporters, defective in beta-sitosterolemia, are also now considered interesting targets in the control and influence of total body sterol homeostasis. In this review, advances referring to the regulation and function of ABCG half-size transporters are summarized and discussed. In addition, new implications for the transcriptional control, as well as the intracellular routing and localization, of these proteins are presented.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2001

Rapid quantification of human ABCA1 mRNA in various cell types and tissues by real-time reverse transcription-PCR.

BACKGROUND: The ABCA1 gene encodes for a member of subfamily A of the ATP-binding cassette transporters that plays an important role in cellular export of cholesterol and phospholipids; therefore, quantification of the ABCA1 mRNA is critical in many studies related to its expression and regulation by metabolic factors, nutritional status, and new antiatherogenic drug candidates. We developed a rapid, sensitive, specific, and reproducible real-time reverse transcription-PCR (RT-PCR) method for detection and quantification of ABCA1 transcripts in total RNA isolated from cultured human cells and tissues. METHODS: To quantify ABCA1 mRNA, we generated a calibration curve from serial dilutions of in vitro-transcribed RNA corresponding to an amplified ABCA1 cDNA 205-bp fragment (homologous calibrator). Two pairs of fluorescent hybridization probes were used to detect the ABCA1 and porphobilinogen deaminase (PBGD) mRNAs; the latter served as an internal control. PCR was performed as real-time amplification of ABCA1 mRNA in 100 ng of total RNA isolated from various human tissues, and cultured cells were calculated from the calibration curve. In addition, normalized values of target (ABCA1/PBGD ratio) were calculated. RESULTS: Using this method, we quantified ABCA1 transcripts in various human tissue samples as well as in monocytes, THP-1 cells, fibroblasts, and adipocytes. We demonstrated ABCA1 mRNA up-regulation during human adipocyte and monocyte differentiation. In addition, we examined the effect of cholesterol loading and deloading on ABCA1 expression in monocytes, THP-1 cells, and fibroblasts. CONCLUSIONS: Our RT-PCR assay allows the specific and highly reproducible detection and quantification of minute amounts of human ABCA1 mRNA. This new method is more accurate, more informative, and less laborious than the classic RT-PCR methods and Northern blot; it therefore could simplify all studies on ABCA1 mRNA expression.

ATP Binding Cassette Transporter 1↗

PubMed2000

Genomic organization and characterization of the promoter of the human ATP-binding cassette transporter-G1 (ABCG1) gene.

The ATP-binding cassette transporter G1 (ABCG1) was recently identified as a regulator of macrophage cholesterol and phospholipid transport. This transporter together with ABCA1 belongs to a group of sterol-sensitive ABC proteins which are induced by lipid loading or specific oxysterols. We report here the genomic structure of ABCG1 along with the 5' flanking sequence using library screening and BLAST search analysis. The ABCG1 gene spans more than 70 kb and contains 15 exons. The exon size is between 30 and 1081 bp and the introns range in size from 137 bp to more than 45 kb. All exon-intron boundaries display the canonical GT/AG sequences. Using promoter-luciferase reporter assays in the myeloid cell lines THP-1 and RAW246.7 and the hepatoma cell line HepG2 we could demonstrate the functionality of the ABCG1 promoter and the minimal sequence requirements for gene expression. The TATA-less proximal promoter contains multiple Sp1 binding sites and a consensus sequence for sterol regulatory element binding protein.

ATP-Binding Cassette Transporters↗

PubMed2000

Transport of lipids from golgi to plasma membrane is defective in tangier disease patients and Abc1-deficient mice.

Mutations in the gene encoding ATP-binding cassette transporter 1 ( ABC1) have been reported in Tangier disease (TD), an autosomal recessive disorder that is characterized by almost complete absence of plasma high-density lipoprotein (HDL), deposition of cholesteryl esters in the reticulo-endothelial system (RES) and aberrant cellular lipid trafficking. We demonstrate here that mice with a targeted inactivation of Abc1 display morphologic abnormalities and perturbations in their lipoprotein metabolism concordant with TD. ABC1 is expressed on the plasma membrane and the Golgi complex, mediates apo-AI associated export of cholesterol and phospholipids from the cell, and is regulated by cholesterol flux. Structural and functional abnormalities in caveolar processing and the trans-Golgi secretory pathway of cells lacking functional ABC1 indicate that lipid export processes involving vesicular budding between the Golgi and the plasma membrane are severely disturbed.

ATP Binding Cassette Transporter 1↗

PubMed2000

Regulation of scavenger receptor CD163 expression in human monocytes and macrophages by pro- and antiinflammatory stimuli.

CD163, also referred to as M130, a member of the scavenger receptor cysteine-rich family (SRCR) is exclusively expressed on cells of the monocyte lineage. In freshly isolated monocytes the CD14bright CD16+ monocyte subset revealed the highest expression of CD163 among all monocyte subsets. CD163 mRNA and protein expression is up-regulated during macrophage colony-stimulating factor (M-CSF)-dependent phagocytic differentiation of human blood monocytes. In contrast, monocytic cells treated with GM-CSF and interleukin-4 (IL-4) for dendritic differentiation down-regulate this antigen. CD163 expression is also suppressed by proinflammatory mediators like lipopolysaccharide (LPS), interferon-gamma (IFN-gamma), and tumor necrosis factor alpha, whereas IL-6 and the antiinflammatory cytokine interleukin-10 (IL-10) strongly up-regulate CD163 mRNA in monocytes and macrophages. The effects of the immunosuppressants dexamethasone, cyclosporin A (CA), and cortisol differ in their capacity to influence CD163 mRNA levels. Our results demonstrate that CD163 expression in monocytes/macrophages is regulated by proinflammatory and antiinflammatory mediators. This expression pattern implies a functional role of CD 163 in the antiinflammatory response of monocytes.

Antigens, CD↗

PubMed1999

Genomic organization and chromosomal localization of the human CD163 (M130) gene: a member of the scavenger receptor cysteine-rich superfamily.

The human protein CD163 (M130) is a member of the scavenger receptor cysteine-rich (SRCR) superfamily, which is exclusively expressed by monocytes and macrophages. Here, we investigated the genomic organization and the chromosomal localization of the human CD163 gene. The CD163 gene is composed of 17 exons and 16 introns and spans over 35 kb. Each of its nine SRCR domains is encoded by a separate exon, which is similar to other members of the group B SRCR subfamily. Two cytoplasmic variants of CD163 arise from alternative splicing of intron 15, while a truncated and an extracellular variant results from alternative splicing of intron 5 or intron 7, respectively. Using fluorescence in situ hybridization we mapped this gene to the human chromosome 12p13. The transcription initiation sites of the CD163 gene were determined and the 5'-flanking region was sequenced. The nucleotide analysis revealed several putative binding sites for transcription factors, which have been shown to play an important role in myeloid specific gene expression. In addition, we identified a L1 element located 1.4 kb upstream of the major transcription initiation site.

Alternative Splicing↗

PubMed1999

Molecular cloning of the human ATP-binding cassette transporter 1 (hABC1): evidence for sterol-dependent regulation in macrophages.

We have cloned the full-length cDNA for the human ATP binding cassette transporter 1 (hABC1). The 6603-bp open reading frame encodes a polypeptide of 2201 amino acids resulting in a deduced molecular weight of 220 kDa. The hABC1 cDNA is highly homologous (62%) to the human rim ABC transporter (ABCR). hABC1 is expressed in a variety of human tissues with highest expression levels found in placenta, liver, lung, adrenal glands, and fetal tissues. We demonstrate that the hABC1 expression is induced during differentiation of human monocytes into macrophages in vitro. In macrophages, both the hABC1 mRNA and protein expression are upregulated in the presence of acetylated low-density lipoprotein (AcLDL). The AcLDL-induced increase in hABC1 expression is reversed by cholesterol depletion mediated by the addition of high-density lipoprotein (HDL3). Our data, demonstrating sterol-dependent regulation of hABC1 in human monocytes/macrophages, suggest a novel role for this transporter molecule in membrane lipid transport.

ATP Binding Cassette Transporter 1↗

PubMed1999

The gene encoding ATP-binding cassette transporter 1 is mutated in Tangier disease.

Tangier disease (TD) is an autosomal recessive disorder of lipid metabolism. It is characterized by absence of plasma high-density lipoprotein (HDL) and deposition of cholesteryl esters in the reticulo-endothelial system with splenomegaly and enlargement of tonsils and lymph nodes. Although low HDL cholesterol is associated with an increased risk for coronary artery disease, this condition is not consistently found in TD pedigrees. Metabolic studies in TD patients have revealed a rapid catabolism of HDL and its precursors. In contrast to normal mononuclear phagocytes (MNP), MNP from TD individuals degrade internalized HDL in unusual lysosomes, indicating a defect in cellular lipid metabolism. HDL-mediated cholesterol efflux and intracellular lipid trafficking and turnover are abnormal in TD fibroblasts, which have a reduced in vitro growth rate. The TD locus has been mapped to chromosome 9q31. Here we present evidence that TD is caused by mutations in ABC1, encoding a member of the ATP-binding cassette (ABC) transporter family, located on chromosome 9q22-31. We have analysed five kindreds with TD and identified seven different mutations, including three that are expected to impair the function of the gene product. The identification of ABC1 as the TD locus has implications for the understanding of cellular HDL metabolism and reverse cholesterol transport, and its association with premature cardiovascular disease.

ATP Binding Cassette Transporter 1↗

PubMed1999

The scavenger receptor CD163: regulation, promoter structure and genomic organization.

CD163 is a recently identified member of the scavenger receptor cysteine-rich superfamily expressed on peripheral blood monocytes and most tissue macrophages. We demonstrate that in vitro culture of human blood monocytes with recombinant M-CSF induces CD163 transcription. In contrast, dendritic differentiation in the presence of GM-CSF and IL-4 suppresses CD163 mRNA and protein levels. Because an important function of CD163 in inflammation has been suggested, we investigated the influence of pro- and anti-inflammatory stimuli on CD163 expression and found a significant suppression by lipoposaccharide and IFN-gamma, whereas IL-10 or dexamethasone strongly induced the expression of CD163. The induction of CD163 mRNA by dexamethasone is suggested to be mediated by several glucocorticoid receptor binding sites located in the proximal promoter region. In addition, this sequence contains potential binding sites for the transcription factors Sp1, C/EBPalpha, Ets-2, PU.1 and AP-1, which have been shown to play an important role in myeloid-specific gene expression. We also identified an L1-transposable element 1.4 kb upstream of the transcription start site that might influence the promoter activity. The function of CD163 may also depend on the use of different isoforms. Several variants of CD163 mRNA have been described that encode proteins with altered cytoplasmic or extracellular domains and thus may differ in their functional properties. We analyzed the genomic organization of the CD163 gene and could demonstrate that these isoforms result from alternative splicing. Further characterization of the isoforms may help to understand the complete function of CD163.

Alternative Splicing↗

PubMed1999

Transcription factors Sp1 and AP-2 mediate induction of acid sphingomyelinase during monocytic differentiation.

Cells from the human monocytic leukemia cell line THP-1 differentiate towards a macrophage-like phenotype when stimulated with phorbol 12-myristate -13- acetate (PMA), 1,25-dihydroxy-vitamin D3, and various other agents. We demonstrate here that the expression of the lysosomal enzyme acid sphingomyelinase (ASM; E.C. 3.1.4.12) is induced during this process and is strongly elevated in differentiated THP-1 cells, as well as in differentiated human mononuclear phagocytes. Using Northern blotting, RNase protection assay, and nuclear run-on analyses, we show that the up-regulation of ASM expression is regulated mainly at the level of transcription and that new protein synthesis is required for enhanced ASM activity. This cell-type specific induction by PMA treatment was further investigated with respect to transcriptional control. A series of 5' deletion derivatives of the upstream regulatory region were used in transient transfection assays to identify promoter elements required for basal and inducible gene expression. A PMA responsive element was localized to a region between -319 and -219 bp upstream of the initiation codon and co-transfections with transcription factor expression plasmids for AP-2 and Sp1 resulted in augmented ASM promoter activity, which was abolished when the binding sites for these two factors were deleted. Using electrophoretic mobility shift assays and supershift assays we demonstrate that this region is specifically bound by Sp1 and AP-2. These factors are present in nuclear extracts prepared from both induced and uninduced THP-1 cells. However, the intensity of the complex formed appeared to increase when nuclear extracts from PMA-treated cells were used. From these studies, we conclude that a concerted action of the transcription factors AP-2 and Sp1 is essential for the up -regulation of ASM expression during the process of macrophage differentiation.

Base Sequence↗

PubMed1998

Identification and characterization of the human adipocyte apM-1 promoter.

The human adipocyte-specific apM-1 gene encodes a secretory protein of the adipose tissue and seems to play a role in the pathogenesis of obesity. A 1.3 kb amount of the proximal promoter region has been cloned and analyzed for the presence of putative transcription factor binding sites. Several binding sites known to be involved in adipogenesis and regulation of adipocyte-specific genes (C/EBP, SREBP) are present. No TATA box, but a classical CCAAT box could be identified. To confirm functionality and cell specificity of the 1.3 kb promoter, a series of 5'-deleted fragments were ligated in front of the luciferase gene and the constructs were transfected into 3T3-L1 adipocytes. The reporter gene was effectively transcribed, as demonstrated by the expression of enzyme activity. The 5'-end of the human cDNA was completed by 5'-RACE-PCR. Several alternative transcription start sites were detected by RNase protection assay and primer extension analysis. In addition, an exon/intron boundary was mapped at the extreme 5'-end of the cDNA sequence. Genomic Southern blotting suggests that the human apM-1 gene is a single copy gene.

Adipocytes↗

PubMed1998

Transcriptional regulation of lysosomal acid lipase in differentiating monocytes is mediated by transcription factors Sp1 and AP-2.

Human lysosomal acid lipase (LAL) is a hydrolase required for the cleavage of cholesteryl esters and triglycerides derived from plasma lipoproteins. It is shown here that during monocyte to macrophage differentiation, the expression of LAL-mRNA is induced. This induction is dependent on protein kinase C activity and protein synthesis. The cell type-specific increase in LAL expression is further investigated in the THP-1 cell line with respect to transcriptional regulation. The human monocytic leukemia cell line THP-1 differentiates into macrophage-like cells when treated with phorbol esters. In order to determine the cis-acting elements necessary for both basal and phorbol 12-myristate-13 acetate (PMA)-enhanced promoter activity, we performed deletion analysis and reporter gene assays. A PMA responsive element has been identified between -182 bp and -107 bp upstream of the major transcription start site. Gel mobility shift assays demonstrated that binding of Sp1 and AP-2 to the LAL promoter is increased by PMA in THP-1 cells. Co-transfections with expression plasmids for Sp1 and AP-2 further emphasized the important role of these transcription factors in both basal and PMA-enhanced LAL expression. Our data suggest that differentiation dependent increase of lysosomal acid lipase (LAL) expression in THP-1 cells is mediated by a concerted action of Sp1 and AP-2.

Cell Differentiation↗