Abstract-Inflammatory or malignant diseases are associated with elevated levels of cytokines and abnormal low density lipoprotein (LDL) cholesterol metabolism. In the acute-phase response to myocardial injury or other trauma or surgery, total and LDL cholesterol levels are markedly decreased. We investigated the effects of the proinflammatory cytokine interleukin (IL)-6 on LDL receptor (LDL-R) function and gene expression in HepG2 cells. IL-6 dose-dependently increased the binding, internalization, and degradation of 125 I-LDL. IL-6 -stimulated HepG2 cells revealed increased steady-state levels of LDL-R mRNA. In HepG2 cells transiently transfected with reporter gene constructs harboring the sequence of the LDL-R promoter extending from nucleotide Ϫ1563 (or from nucleotide Ϫ234) through Ϫ58 relative to the translation start site, IL-6 dose-dependently increased promoter activity. In the presence of LDL, a similar relative stimulatory effect of IL-6 was observed. Studies using a reporter plasmid with a functionally disrupted sterol-responsive element (SRE)-1 revealed a reduced stimulatory response to IL-6. In gel-shift assays, nuclear extracts of IL-6 -treated HepG2 cells showed an induced binding of SRE binding protein (SREBP)-1a and SRE binding protein(SREBP)-2 to the SRE-1 that was independent of the cellular sterol content and an induced binding of Sp1 and Sp3 to repeat 3 of the LDL-R promoter. Our data indicate that IL-6 induces stimulation of the LDL-R gene, resulting in enhanced gene transcription and LDL-R activity. This effect is sterol independent and involves, on the molecular level, activation of nuclear factors binding to SRE-1 and the Sp1 binding site in repeat 2 and repeat 3 of the LDL-R promoter, respectively.

A major physiological feedback mechanism of cholesterol in transcription of a number of lipid metabolismrelated genes is mediated by sterol regulatory elements (SREs) and their binding proteins (SREBPs). Polyunsaturated free fatty acids alone, as well as synergistically with sterols, decrease SRE-mediated gene expression up to 80% in a dose-dependent manner by decreasing levels of the active transcription factor SREBP. We investigated potential mechanisms for this effect. We hypothesized that free fatty acids reduce SREBP-mediated gene transcription by increasing intracellular cholesterol content through the hydrolysis of cellular sphingomyelin, which has a high affinity for free cholesterol. We also questioned whether the lipid second messenger ceramide, a product of sphingomyelin hydrolysis, can decrease SRE-mediated gene transcription. We found that addition of ceramide analogs alone and additively with fatty acids decreased SRE expression and that ceramide analogs reduced levels of the transcriptionally active forms of SREBP-1 and SREBP-2. Increasing intracellular ceramide levels by exogenous sphingomyelinase or inhibition of ceramidase decreased SREmediated gene expression. None of the above conditions induced apoptosis. Incubation with U18666A, a compound that inhibits intracellular cholesterol movement, increased SRE-mediated gene transcription. C 2 -ceramide abrogated the effect of U18666A on SRE-mediated gene transcription, suggesting cholesterol-independent regulation of SREBP. We provide evidence that sphingomyelin hydrolysis and intermediates of sphingomyelin metabolism (in addition to cholesterol and fatty acids) contribute to regulation of SRE-mediated gene transcription.Fatty acids and cholesterol interact at a number of metabolic levels. Both contribute to the composition of circulating lipoproteins and cellular membranes. Clinically, higher intakes of polyunsaturated free fatty acids are linked to lower levels of low density lipoprotein cholesterol, whereas higher intakes of saturated and trans-fatty acids correlate with increased low density lipoprotein cholesterol and decreased high density lipoprotein cholesterol as well as increased risk for cardiovascular disease (1). At the cellular level, cholesterol and fatty acids are linked to the regulation of intracellular cholesterol levels by activation of acyl-CoA:cholesterol acyltransferase (2, 3). Of relevant interest, genes regulating both cholesterol and fatty acid metabolism contain sterol regulatory elements (SREs) 1 in their promoter regions. Still, little information is available on possible interactions between fatty acids and cholesterol in the regulation of gene transcription.SRE-binding proteins (SREBPs) are transcription factors that are post-transcriptionally regulated. SREBP in its precursor form is located in the endoplasmic reticulum, where it is bound at the C-terminal end to the SREBP cleavage-activating protein. In sterol depletion, both proteins are translocated to the Golgi apparatus (4, 5). Sequential cleavage by two proteas...

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Summary.Genotyping of human platelet alloantigens (HPA) has become an important procedure in the diagnosis and prevention of disorders such as neonatal alloimmune thrombocytopenic purpura, post-transfusion purpura, and refractoriness to platelet transfusion therapy. We present a single-tube method for HPA-1 genotyping that combines rapid-cycle PCR with allele-specific fluorescent probe melting profiles for product genotyping. A fragment covering the polymorphic site is amplified in the presence of two fluorescentlylabelled hybridization probes. During the annealing step of the thermal cycling, both probes bind to their complementary sequences in the amplicon resulting in resonance energy transfer, thus providing real-time fluorescence monitoring of PCR. Continuous aquisition of fluorescence data during a melting curve analysis at the completion of PCR revealed that loss of fluorescence occurred in an allele-specific manner as the detection probe, which was fully complementary to the HPA-1b allele, melted off the template. By determining the temperature at which maximum melting of the hybrids occurred, the two alleles were readily distinguishable. Using this method, genotyping of 32 samples was completed within 30 min without the need for any post-PCR sample manipulation, thereby eliminating the risks of end-product contamination and sample tracking errors. The genotypes determined with the LightCycler TM were identical when compared with a conventional PCR and restriction fragment length polymorphism technique. The genotyping of HPA-1 on the LightCycler is a rapid and reliable method that is suitable for typing both small and large numbers of samples.

In order to identify mutations in the low density lipoprotein receptor (LDLR) gene in primary hypercholesterolemia, we screened 100 unrelated German individuals with elevated plasma LDL-C (LDL-C > 4,7 mmol/l) for mutations in the 18 exons and their flanking intronic sequences including the promoter region of the LDL-R gene using a combination of polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) and direct sequencing. In addition we tested all patients for the presence of mutations in codons 3456 -3553 of the gene encoding apolipoprotein B-100. In 56 individuals we detected 37 different mutations affecting the LDL-R gene, 16 of which, designated C122R, C127Y, C163W, F179L, R236W, E296X, R553C, V618D, T721I, V785D, G1358+2A, 257delTCTGGAGGT, 657delC, 676insACGGTATGGACTGCAdelGACG, C1205delTCT, 2420delTCCTTCT, have not yet been reported. One proband was a compound heterozygote showing two separate sequence variations (E207X and T705I). Seven patients were heterozygous for the mutation R3500Q within the apoB-100 gene. These results demonstrate that there is a broad spectrum of mutations in the LDL-R gene and that the R3500Q mutation is a frequent cause of hypercholesterolemia in the German population.