Regulation of MHC class II gene expression.
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Gene Expression Regulation↗
Biomedical subjects
W Reith
Publications and source records attributed to W Reith.
Decompressive craniectomy for cerebral infarction. An experimental study in rats.
BACKGROUND AND PURPOSE: Acute ischemia in the territory of the carotid artery can lead to massive cerebral edema with raised intracranial pressure and progression to coma and death due to uncal, cingulate, or tonsillar herniation. Thus far, only anecdotal experience with supratentorial ischemia treated by decompressive craniectomy has been reported; and there are no published experimental data dealing with this kind of therapy in acute supratentorial stroke. In this study, we present our results on the effect of decompressive craniectomy in an endovascular model of cerebral infarction in rats. METHODS: Focal cerebral ischemia was induced in 50 rats using an endovascular occlusion technique of the middle cerebral artery. Decompressive craniectomy was performed in 30 animals: in 15 animals after 1 hour and in the remaining 15 animals 24 hours after vessel occlusion. Twenty animals were not treated by decompressive craniectomy (control group). RESULTS: Mortality in the nontreated group was 35%, whereas none of the animals treated by decompressive craniectomy died. Neurological behavior, weight loss, and infarction size were all significantly better in the animals treated by decompressive craniectomy, regardless of whether they had been treated after 1 or 24 hours (P < .01). CONCLUSIONS: Our results suggest that decompressive craniectomy for cerebral ischemia not only reduces mortality but also significantly improves outcome and reduces infarction size, probably because of increased perfusion pressure through leptomeningeal collaterals. This experimental study suggests that a controlled study of decompressive craniectomy in patients with acute internal carotid or middle cerebral artery occlusion would be worthwhile. By performing decompressive craniectomy in a small, selected group of patients, neurosurgeons may play an important role in the management of these patients.
Acute Disease↗
Multislice diffusion mapping for 3-D evolution of cerebral ischemia in a rat stroke model.
Diffusion-weighted magnetic resonance imaging (DWI) can quantitatively demonstrate cerebral ischemia within minutes after the onset of ischemia. The use of a DWI echo-planar multislice technique in this study and the mapping of the apparent diffusion coefficient (ADC) of water, a reliable indicator of ischemic regions, allow for the detection of the three-dimensional (3-D) evolution of ischemia in a rat stroke model. We evaluated 13 time points from 5 to 180 minutes after occlusion of the middle cerebral artery (MCA) and monitored the 3-D spread of ischemia. Within 5 minutes after the onset of ischemia, regions with reduced ADC values occurred. The core of the lesion, with the lowest absolute ADC values, first appeared in the lateral caudoputamen and frontoparietal cortex, then spread to adjacent areas. The volume of ischemic tissue was 224 +/- 48.5 mm3 (mean +/- SEM) after 180 minutes, ranging from 92 to 320 mm3, and this correlated well with the corrected infarct volume at postmortem (194 +/- 23.1 mm3, r = 0.72, p < 0.05). This experiment demonstrated that 3-D multislice diffusion mapping can detect ischemic regions noninvasively 5 minutes after MCA occlusion and follow the development of ischemia. The distribution of changes in absolute ADC values within the ischemic region can be followed over time, giving important information about the evolution of focal ischemia.
Animals↗
Early MR detection of experimentally induced cerebral ischemia using magnetic susceptibility contrast agents: comparison between gadopentetate dimeglumine and iron oxide particles.
PURPOSE: To evaluate early patterns of MR changes in a rat model of cerebral ischemia using the first pass of two magnetic susceptibility contrast agents. METHODS: One hours after endovascular middle cerebral artery occlusion, all animals were examined in an experimental MR unit. After bolus application of gadopentetate dimeglumine and, 10 minutes later, of iron oxide particles, the MR changes of the first pass of these contrast agents were followed using a T2*-weighted fast low-angle shot sequence. Time-density curves of both contrast agents were analyzed and compared. RESULTS: After bolus injection of either (paramagnetic) gadopentetate dimeglumine or superparamagnetic particles, nonischemic brain parenchyma decreased markedly in signal, whereas the ischemic brain area remained relatively hyperintense (and thus became clearly delineated). Only after application of gadopentetate dimeglumine did a mild reduction in signal occur in the ischemic hemisphere, although the main artery was occluded. An explantation for this phenomenon might be residual capillary perfusion (plasma flow), which is detectable only when the smaller (paramagnetic) contrast molecules are being used. CONCLUSIONS: Cerebral perfusion deficits can be detected 1 hour after vascular occlusion with T2*-weighted fast low-angle shot sequences and bolus injection of paramagnetic or superparamagnetic MR contrast agents. Gadopentetate dimeglumine may be used as a marker of microcirculatory plasma flow.
Animals↗
Developmental extinction of major histocompatibility complex class II gene expression in plasmocytes is mediated by silencing of the transactivator gene CIITA.
Constitutive major histocompatibility complex (MHC) class II gene expression is tightly restricted to antigen presenting cells and is under developmental control. Cells of the B cell lineage acquire the capacity to express MHC class II genes early during ontogeny and lose this property during terminal differentiation into plasma cells. Cell fusion experiments have suggested that the extinction of MHC class II expression in plasma cells is due to a dominant repression, but the underlying mechanisms are not understood. CIITA was recently identified as an MHC class II transactivator that is essential for MHC class II expression in B lymphocytes. We show here that inactivation of MHC class II genes in plasmocytes is associated with silencing of the CIITA gene. Moreover, experimentally induced expression of CIITA in plasmocytes leads to reexpression of MHC class II molecules to the same level as that observed on B lymphocytes. We therefore conclude that the loss of MHC class II expression observed upon terminal differentiation of B lymphocytes into plasmocytes results from silencing of the transactivator gene CIITA.
B-Lymphocytes↗
Cooperative binding between factors RFX and X2bp to the X and X2 boxes of MHC class II promoters.
Transcription of major histocompatibility complex (MHC) class II genes is controlled primarily by the promoter, which contains several conserved cis-acting elements, including the X, X2, and Y boxes. We show here that RFX, the X box-binding protein that is deficient in certain MHC class II regulatory mutants, binds cooperatively with an X2 box-binding protein (X2bp) to form an RFX.X2bp.DNA complex in which the interaction of the two factors with their target sites is strongly stabilized. A functional role of this RFX.X2bp complex is consistent with mutational analysis of the X and X2 boxes of the DRA and DRB1 class II promoters. Together with previous results demonstrating cooperative binding between RFX and the Y box-binding protein NF-Y, our results indicate that RFX plays a central role in promoting cooperative binding interactions required for stable occupation of the MHC class II promoter. This may explain why the highly specific defect in binding of RFX observed in certain MHC class II regulatory mutants is associated in vivo with a bare promoter in which all of the cis-acting elements, including the X, X2, and Y boxes, are unoccupied.
Base Sequence↗
Function of major histocompatibility complex class II promoters requires cooperative binding between factors RFX and NF-Y.
Transcription of major histocompatibility complex (MHC) class II genes is controlled largely by the conserved promoter elements called the X and Y boxes. We show here that RFX, the X box-binding protein deficient in certain MHC class II-deficient immunodeficiency patients (CID), and the Y box-binding protein NF-Y bind cooperatively. Functional relevance of this protein-protein interaction is suggested by the fact that promoter activity correlates with cooperative binding of RFX and NF-Y rather than with binding of RFX or NF-Y alone. Stability of the RFX/NF-Y complex is affected by alterations in X-Y box spacing. These results are consistent with the fact that MHC class II promoter function is dependent on correct stereospecific alignment of the X and Y boxes. Cooperative binding involving RFX, NF-Y, and perhaps other MHC class II promoter-binding proteins may explain why the highly specific defect in binding of RFX observed in CID cells is associated in vivo with a bare promoter in which all of the cis-acting elements, including the X and Y boxes, are unoccupied.
Base Sequence↗
MRI monitoring of experimental cerebral ischaemia: comparison of two models.
In experimental stroke research one of the key questions is whether animals models truly reflect human disease. One important reason for modelling stroke is to produce tissue changes that can be used to validate the correlation between the results of advanced radiological imaging and pathology. The aim of this study was to compare two minimally invasive rat models of focal ischaemic stroke as to their ability to simulate clinical stroke reproducibly. In one model a focal infarct was induced using the photochemical Rose Bengal technique. The second model was based on transvascular occlusion of the middle cerebral artery using a cervical approach. In all animals we performed MRI at different times with two different paramagnetic contrast agents. The time course of blood-brain-barrier disruption in the Rose Bengal model differed entirely from that in human brain ischaemia. The experimental stroke showed marked contrast enhancement in the first hour after the onset of ischaemia. On the other hand, the MRI changes in the suture occlusion model were very similar to the changes observed in human brain ischaemia: no early disruption of the blood-brain-barrier and increased T2-signal 4-6 h after the onset of stroke. We hope that the suture occlusion model will be used for research not only by basic and clinical scientists but also by radiologists, who, using modern imaging methods, may greatly influence the diagnosis as well as the management of this devastating disease.
Animals↗
MRI in acute cerebral ischaemia: perfusion imaging with superparamagnetic iron oxide in a rat model.
An imaging technique capable of detecting ischaemic cerebral injury at an early stage could improve diagnosis in acute or transient cerebral ischaemia. We compared the ability of superparamagnetically contrast-enhanced MRI and conventional T2-weighted MRI to detect ischaemic injury early after unilateral occlusion of the middle cerebral artery in 12 male Wistar rats. Permanent vessel occlusion was achieved by a transvascular approach, which has the advantage of not requiring a craniectomy. At 45-60 min after the procedure, the animals had conventional T2-weighted MRI before and after administration of a superparamagnetic contrast agent (iron oxide particles). Unenhanced images were normal in all animals. After administration of iron oxide particles, the presumed ischaemic area was clearly visible, as relatively increased signal, in all animals; this high signal area corresponded to the area of ischaemic brain infarction seen on histological studies. Magnetic susceptibility effects of iron particles cause low signal in normally perfused cerebral tissue, whereas tissue with reduced or absent blood flow continues to give relatively high signal. Our results suggest that superparamagnetic iron particles may significantly reduce the interval between an ischaemic insult and the appearance of parenchymal changes on MRI.
Acute Disease↗
Laser Doppler flowmetry of focal ischaemia and reperfusion in deep brain structures in rats.
Monitoring cerebral blood flow during focal ischaemia and reperfusion with established techniques such as hydrogen clearance and autoradiography is difficult. Laser Doppler flowmetry is a new technique, it allows one to continuously measure blood flow in small tissue samples. The objective of this study was to compare laser Doppler flowmetry with hydrogen clearance using a new single fiber probe to obtain measurements in deep brain structures and then to show the temporal profile of cerebral blood flow during focal ischaemia and after reperfusion. First, the single fiber laser Doppler method was compared with the hydrogen clearance method in ten Wistar rats. Second, focal cerebral ischaemia was induced in fifteen Wistar rats using a model of middle cerebral artery occlusion based on the intravascular insertion of a nylon suture; reperfusion occurred after withdrawal of the suture. The laser Doppler probe was placed in the lateral caudatoputamen, and local cerebral blood flow was measured continuously before and during occlusion as well as after reperfusion. The relative blood flow values obtained by the laser Doppler method and the hydrogen clearance method showed a good correlation (r = 0.76) and a linear relationship. A rapid decrease in laser Doppler flowmetry to 42 +/- 16% of former baseline values was seen with occlusion of the middle cerebral artery; during occlusion cerebral blood flow remained at this level. Reperfusion resulted in a heterogeneous pattern of cerebral blood flow as laser Doppler flowmetry values ranged from 25% to 134% of baseline values. The effects of middle cerebral artery occlusion and reperfusion on cerebral blood flow can be monitored on-line with laser Doppler flowmetry.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
MHC class II-deficient combined immunodeficiency: a disease of gene regulation.
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Base Sequence↗
Functional complementation of major histocompatibility complex class II regulatory mutants by the purified X-box-binding protein RFX.
Major histocompatibility complex (MHC) class II deficiency, or bare lymphocyte syndrome (BLS), is a disease of gene regulation. Patients with BLS have been classified into at least three complementation groups (A, B, and C) believed to correspond to three distinct MHC class II regulatory genes. The elucidation of the molecular basis for this disease will thus clarify the mechanisms controlling the complex regulation of MHC class II genes. Complementation groups B and C are characterized by a lack of binding of RFX, a nuclear protein that normally binds specifically to the X box cis-acting element present in the promoters of all MHC class II genes. We have now purified RFX to near homogeneity by affinity chromatography. Using an in vitro transcription system based on the HLA-DRA promoter, we show here that extracts from RFX-deficient cells from patients with BLS (BLS cells) in groups B and C, which are transcriptionally inactive in this assay, can be complemented to full transcriptional activity by the purified RFX. As expected, purified RFX also restores a completely normal pattern of X box-binding complexes in these mutant extracts. This provides the first direct functional evidence that RFX is an activator of MHC class II gene transcription and that its absence is indeed responsible for the regulatory defect in MHC class II gene expression in patients with BLS.
Base Sequence↗
RFX1, a transactivator of hepatitis B virus enhancer I, belongs to a novel family of homodimeric and heterodimeric DNA-binding proteins.
RFX1 is a transactivator of human hepatitis B virus enhancer I. We show here that RFX1 belongs to a previously unidentified family of DNA-binding proteins of which we have cloned three members, RFX1, RFX2, and RFX3, from humans and mice. Members of the RFX family constitute the nuclear complexes that have been referred to previously as enhancer factor C, EP, methylation-dependent DNA-binding protein, or rpL30 alpha. RFX proteins share five strongly conserved regions which include the two domains required for DNA binding and dimerization. They have very similar DNA-binding specificities and heterodimerize both in vitro and in vivo. mRNA levels for all three genes, particularly RFX2, are elevated in testis. In other cell lines and tissues, RFX mRNA levels are variable, particularly for RFX2 and RFX3. RFX proteins share several novel features, including new DNA-binding and dimerization motifs and a peculiar dependence on methylated CpG dinucleotides at certain sites.
Alternative Splicing↗
[Radiology of cerebrovascular malformations].
Cerebral vascular malformations are, after hypertension, the second most frequent cause of non-traumatic, intracerebral hemorrhage. A reliable intravital diagnosis only became possible with radiological diagnostic methods which also contributed significantly to the development of therapeutic concepts. Diagnostic and therapeutic possibilities for the various forms of cerebral vascular malformations are surveyed in the present review. Since radiology occupies a central position in the diagnosis and (in the meantime also) therapy of cerebral vascular malformations, epidemiological and prognostic factors are also discussed in detail.
Brain Neoplasms↗
Clathrin-coated pit-mediated receptor internalization. Role of internalization signals and receptor mobility.
Most signals controlling receptor-mediated endocytosis have been identified by alteration of sequences present in receptors normally internalized via clathrin-coated pits. In the present work we have reconsidered the factors that control internalization the other way around: i.e. by introducing potential internalization sequences in complement receptor 1 (CR1) which does not preferentially associate with clathrin-coated pits. The analysis of the internalization efficiency of NPxY related motifs generated by substituting His2010 and/or Glu2015 by either Phe or Tyr indicates that FxNPxY is the stronger promoter of endocytosis and that the signal efficiency depends on the presence of aromatic residues (including a tyrosine) at both ends of the -xNPx- motif. Moreover, CR1-tyr (substitution of Glu2015 for Tyr) internalization was superposable to that of a receptor composed of the extracellular and transmembrane domains of CR1 fused to the intracytoplasmic tail of the low density lipoprotein (LDL) receptor (including the FxNPxY motif) (CR1-LDL). When analyzed by fluorescence recovery after photobleaching, the surface mobility of CR1-LDL was decreased as compared with that of either CR1-tyr or CR1-wt, despite a similar association with clathrin-coated pits. The role of receptor mobility in internalization was confirmed by the observation that CR1-tl, with a deletion of the cytoplasmic tail, was more mobile and more efficiently internalized than CR1-wt.
Amino Acid Sequence↗
The different level of expression of HLA-DRB1 and -DRB3 genes is controlled by conserved isotypic differences in promoter sequence.
HLA-DRB1 and -DRB3 are two genes encoding two distinct HLA-DR beta chains in the DRw52 family of haplotypes (DR3, DR5, DR13, and DR14). These beta chains determine the structural and functional identity of the two kinds of HLA-DR molecules expressed. The highly polymorphic HLA-DRB1 locus is always expressed at a higher level than the HLA-DRB3 locus, and functional assays indicate that the proximal promoter of DRB1 is indeed more active than that of DRB3. The DNA sequence of the two promoters in nine different DRw52 haplotypes has revealed a stricking allelic conservation as well as characteristic, isotype-specific, conserved-sequence motifs. These isotype-specific differences concern the functionally essential X and Y box motifs of HLA class II promoters, and they do indeed affect binding of specific nuclear factors to the X and Y boxes of DRB1 or DRB3 promoters. Finally, analysis of the activity of various normal and mutated DRB1 or DRB3 promoters indicates that the X box region of these promoters plays a dominant role in controlling the relative levels of HLA-DRB1 and -DRB3 gene expression.
Alkaline Phosphatase↗
RFX1 is identical to enhancer factor C and functions as a transactivator of the hepatitis B virus enhancer.
Hepatitis B virus gene expression is to a large extent under the control of enhancer I (EnhI). The activity of EnhI is strictly dependent on the enhancer factor C (EF-C) site, an inverted repeat that is bound by a ubiquitous nuclear protein known as EF-C. Here we report the unexpected finding that EF-C is in fact identical to RFX1, a novel transcription factor previously cloned by virtue of its affinity for the HLA class II X-box promoter element. This finding has allowed us to provide direct evidence that RFX1 (EF-C) is crucial for EnhI function in HepG2 hepatoma cells; RFX1-specific antisense oligonucleotides appear to inhibit EnhI-driven expression of the hepatitis B virus major surface antigen gene, and in transfection assays, RFX1 behaves as a potent transactivator of EnhI. Interestingly, transactivation of EnhI by RFX1 (EF-C) is not observed in cell lines that are not of liver origin, suggesting that the ubiquitous RFX1 protein cooperates with liver-specific factors.
Animals↗
[Radiology of stroke].
Today radiologic methods play an important role in the diagnosis of cerebral stroke. The aim of the radiologist, however, should not only be to classify the stroke into the four main categories (ischemic stroke, intracerebral bleeding, subarachnoid hemorrhage, sinovenous thrombosis), but also to interpret the findings with regard to the etiology of the disease. The pattern of lesions gives information about the etiology of ischemic stroke; the correct interpretation of these lesion patterns allows one to optimize therapeutic decisions. This paper additionally focuses on the differential diagnosis of intracerebral hemorrhage and the CT and MR signs of sinovenous thrombosis. New developed concepts in the field of stroke therapy and prophylaxis call for authority and continuous education of the radiologist on this topic. Pure descriptions of radiologic findings without an understanding of the pathogenesis of the disease will be ignored by the clinician. On the other hand, the radiologist can turn the therapeutic decisions in the right direction by combining morphological descriptions with pathogenetic orientated interpretations. In this way, the radiologist can contribute to the reduction of costs in the public health system.
Cerebrovascular Disorders↗