Multiple genes encode nuclear factor 1-like proteins that bind to the promoter for 3-hydroxy-3-methylglutaryl-coenzyme A reductase

DNA-binding proteins of the nuclear factor 1 (NF1) family recognize sequences containing TGG. Two of these proteins, termed reductase promoter factor (RPF) proteins A and B, bind to the promoter for hamster 3-hydroxy-3-methylglutaryl-coenzyme A reductase, a negatively regulated enzyme in cholesterol biosynthesis. In the current study, we determined the sequences of peptides derived from hamster RPF proteins A and B and used this information to isolate a cDNA, designated pNF1/Red1, that encodes RPF protein B. The peptide sequence of RPF protein A, the other reductase-related protein, suggests that it is the hamster equivalent of NF1/L, which was previously cloned from rat liver. We also isolated a hamster cDNA for an additional member of the NF1 family, designated NF1/X. Thus, the hamster genome contains at least three genes for NF1-like proteins. It is likely to contain a fourth gene, corresponding to NF1/CTF, which was previously cloned from the human. The NH2-terminal sequences of all four NF1-like proteins (NF1/Red1, NF1/L, NF1/X, and NF1/CTF), which are virtually identical, contain the DNA-binding domain that recognizes TGG. Functional diversity may arise from differences in the COOH-terminal sequences. We hypothesize that the COOH-terminal domain interacts with adjacent DNA-binding proteins, thereby stabilizing the binding of a particular NF1-like protein to a particular promoter. This protein-protein interaction confers specificity to a class of proteins whose DNA-recognition sequence is widespread in the genome. Sterols may repress transcription of the reductase gene by disrupting this protein-protein interaction.

Localization of mRNA for low density lipoprotein receptor and a cholesterol synthetic enzyme in rabbit nervous system by in situ hybridization

The low density lipoprotein receptor and one of its ligands, apoprotein E, are known to be synthesized in the central nervous system. In the current study, we used in situ hybridization to localize the receptor mRNA in selected neurons and glia throughout the nervous system of 9-day-old rabbits. Particularly high levels were found in sensory ganglia, sensory nuclei, and motor-related nuclei. The same regions contained high levels of mRNA for 3-hydroxy-3-methylglutaryl-coenzyme A synthase, a regulated enzyme in cholesterol biosynthesis. The distribution of low density lipoprotein receptor mRNA was similar in mature and immature rabbits. The data suggest that certain cells in the nervous system have high requirements for cholesterol, which they satisfy through cholesterol synthesis and through receptor-mediated uptake of cholesterol-carrying lipoproteins. The latter originate in astrocytes which synthesize and secrete apoprotein E. These data suggest that the nervous system of mammals contains an active system for continuous redistribution and recycling of cholesterol that is physically distinct from the lipoprotein transport system in plasma.

Prevention of accidental extubation in newborns

Maintaining endotracheal intubation is critical to treating respiratory failure in newborns. To reduce accidental extubations in our neonatal intensive care unit, a prospective comparison of rates of extubation was made between two taping methods and whether or not a head restraint was used. One tape method was significantly better at preventing accidental extubations. Head restraint was not a benefit when used prospectively. Factors that preceded or were associated with accidental extubation included the time intubated, infant agitation, endotracheal tube suctioning, the infant turning its head, chest physiotherapy, loose tape, too short a tube between lip and adapter, weighing, and endotracheal tube taping. This information and the study design are valuable in developing strategies to minimize accidental endotracheal extubation and the subsequent risks of airway injury and subglottic stenosis in sick newborns.

A pilot outreach program for small quantity generators of hazardous waste

The Massachusetts Department of Environmental Management initiated a pilot project to improve compliance with hazardous waste regulations and management of hazardous wastes with auto body shops around the state. The program consisted of mass mailings, a series of workshops throughout the state, a coordinated inspection program by the state regulatory agency, and technology transfer. At the start of the program in January 1986, approximately 650 of the estimated 2,350 auto body shops in the state had notified EPA of their waste generating activities; by January 1987, approximately 1,200 shops had done so. Suggestions for improving program efforts include tailoring the outreach effort to the industry, government-sponsored research and development directed at the needs of small firms, mandatory participation in hazardous waste transportation programs, and better coordination by EPA of its information collection and distribution program.

Detection of neonatal hypoglycemia--a comparison of three reagent strips

This article reports two studies that replicate previous investigations of the effectiveness of Chemstrip bG, Dextrostix and Visidex for making nursing assessments of hypoglycemia in the newborn. The article also describes a third study that combines results of the first two studies with results of previous studies in the literature in an attempt to improve the reliability and validity of the findings. In the first study, 102 blood samples were tested using either Chemstrip bG or Dextrostix and then compared with laboratory blood glucose levels. Because of the small number of hypoglycemic samples, a second study was devised in which six samples of cord blood were artificially titrated to known levels of glucose. In this study, Visidex as well as Chemstrip bG and Dextrostix were used. Eighty-five percent, 50 percent and 90.4 percent of the hypoglycemic samples were detected by Chemstrip bG, Dextrostix and Visidex, respectively. Data available in the literature from previous studies investigating the same question were then compiled and analyzed. The composite sample of 402 infants for Dextrostix and 484 for Chemstrip bG resulted in the finding that less than half of the hypoglycemic infants tested with Dextrostix were detected whereas Chemstrip bG detected 90 percent of them. The conclusion reached is that both Chemstrip bG and Visidex can be considered adequate screening techniques for nursing assessment of hypoglycemia in the newborn, while visually read Dextrostix is unacceptable in clinical practice.

Mutational analysis of the ligand binding domain of the low density lipoprotein receptor

The ligand binding domain of the low density lipoprotein (LDL) receptor contains seven imperfect repeats of a 40-amino acid cysteine-rich sequence. Each repeat contains clustered negative charges that have been postulated as ligand-binding sites. The adjacent region of the protein, the growth factor homology region, contains three cysteine-rich repeats (A-C) whose sequence differs from those in the ligand binding domain. To dissect the contribution of these different cysteine-rich repeats to ligand binding, we used oligonucleotide-directed mutagenesis to alter expressible cDNAs for the human LDL receptor which were then introduced into monkey COS cells by transfection. We measured the ability of the mutant receptors to bind LDL, which contains a single protein ligand for the receptor (apoB-100), and beta-migrating very low density lipoprotein (beta-VLDL), which contains apoB-100 plus multiple copies of another ligand (apoE). The results show that repeat 1 is not required for binding of either ligand. Repeats 2 plus 3 and repeats 6 plus 7 are required for maximal binding of LDL, but not beta-VLDL. Repeat 5 is required for binding of both ligands. Repeat A in the growth factor homology region is required for binding of LDL, but not beta-VLDL. Repeat B is not required for ligand binding. These results support a model for the LDL receptor in which various repeats play additive roles in ligand binding, each repeat making a separate contribution to the binding event.

Multivalent control of 3-hydroxy-3-methylglutaryl coenzyme A reductase. Mevalonate-derived product inhibits translation of mRNA and accelerates degradation of enzyme

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) is subject to multivalent feedback suppression mediated by sterols and non-sterol substances derived from mevalonate, the product of the enzyme. To dissect the mechanism for this multivalent effect, Chinese hamster ovary cells were incubated with sterols contained in plasma lipoproteins and with a high concentration (100 microM) of compactin, an inhibitor of the reductase. Under these conditions, the amounts of HMG-CoA reductase protein and catalytic activity were high, although the cells were saturated with sterols, as reflected by active synthesis of cholesteryl esters. The amount of enzyme fell by 99% when the cells received excess mevalonate in addition to sterols. This decline was not associated with a fall in levels of reductase messenger RNA (mRNA). Rather, it was attributable to an 80% decline in translation of the mRNA, coupled with a 5-fold increase in the rate of degradation of reductase protein, as revealed by pulse-chase experiments with [35S]methionine. Considered together with previous data, these findings suggest a multilevel mechanism for multivalent regulation of HMG-CoA reductase. We suggest that sterols suppress the enzyme incompletely by partially repressing transcription of the gene and that nonsterol products derived from mevalonate further reduce the enzyme by inhibiting translation of the mRNA. Sterols and non-sterol products, acting together, accelerate the degradation of reductase protein. This combination of transcriptional and posttranscriptional controls can regulate the amount of reductase protein over a several hundred-fold range in animal cells.

Human low density lipoprotein receptor expressed in Xenopus oocytes. Conserved signals for O-linked glycosylation and receptor-mediated endocytosis

The human low density lipoprotein (LDL) receptor is shown to carry out efficient receptor-mediated endocytosis in Xenopus laevis oocytes. Microinjection of mRNAs encoding the human receptor led to synthesis of a 120-kDa precursor possessing high mannose N-linked sugars and core O-linked sugars. During its transport to the cell surface, the protein increased in apparent size to 160 kDa, which is similar to the change that occurs in human cells. This increase was not seen when the receptor lacked the serine/threonine-rich region that undergoes O-linked glycosylation. The surface receptors bound 125I-LDL at 0 degrees C and internalized it with a half-time of 2 min when the cells were warmed to 19 degrees C. The rate of internalization was slowed by 7-fold when a single residue in the cytoplasmic domain (Tyr807) was changed to a cysteine, an alteration that slows incorporation into coated pits in mammalian cells. Deletion of the cytoplasmic domain abolished rapid internalization. We conclude that the signals for O-linked glycosylation and receptor-mediated endocytosis of the LDL receptor have been conserved throughout vertebrate evolution.

Immunocytochemical localization of mutant low density lipoprotein receptors that fail to reach the Golgi complex

In the low density lipoprotein (LDL) receptor system, blocks in intracellular movement of a cell surface receptor result from naturally occurring mutations. These mutations occur in patients with familial hypercholesterolemia. One class of mutant LDL receptor genes (class 2 mutations) produces a receptor that is synthesized and glycosylated in the endoplasmic reticulum (ER) but does not reach the cell surface. These receptors contain serine/threonine-linked (O-linked) carbohydrate chains with core N-acetylgalactosamine residues and asparagine-linked (N-linked) carbohydrate chains of the high mannose type that are only partially trimmed. To determine the site of blockage in transport, we used electron microscope immunohistochemistry to compare the intracellular location of LDL receptors in normal human fibroblasts with their location in class 2 mutant fibroblasts. In normal cells, LDL receptors were located in coated pits, coated vesicles, endosomes, multivesicular bodies, and portions of the Golgi complex. In contrast, the mutant receptors in class 2 cells were almost entirely confined to rough ER and irregular extensions of the rough ER. Metabolic labeling studies with [3H]glucosamine confirmed that these mutant receptors contain core O-linked sugars, suggesting that the enzymes that attach these residues are located in the rough ER or the transitional zone of the ER. These studies establish that naturally occurring mutations in cell surface receptors can cause the receptors to remain trapped in the ER, thereby preventing their normal function and producing a genetic disease.

Type A behavior and cardiovascular responsivity in preschoolers

Type A behavior was investigated in preschool children in relation to cardiovascular reactivity. One hundred forty-four children from 3 1/2 to 6 1/2 years of age were categorized by their teachers according to the Matthews Youth Test for Health as Type A, Mixed, or Type B. The children's pulse, pulse rate variability, and blood pressure were then measured at rest and during a challenging situation. Analysis of covariance indicated that Type A children showed a significantly greater systolic rise to challenge than did Type B children, a finding similar to that of Type A adults, college students, and adolescents.

The Glycine-Glomus-Rhizobium Symbiosis : VII. Photosynthetic Nutrient-Use Efficiency in Nodulated, Mycorrhizal Soybeans

Four consecutive trifoliate leaves of 56-day-old symbiotic or nonsymbiotic soybean plants were evaluated individually for CO(2) exchange rates (CER), leaf area and dry weight, and leaf N, P, and starch concentrations. Plants had been inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae and Rhizobium japonicum, with either of the endophytes alone, or with neither at time of planting. Plants lacking one or both endophytes received N and/or P fertilizers to produce plants of equal total leaf dry weight in all four treatments. Photosynthetic P-use efficiency (CER per unit leaf P) was higher in the leaves of VAM plants than in P-fertilized plants regardless of the N source (N(2) fixation or combined N). Photosynthetic N-use efficiency was also higher in VAM than in non-VAM plants, but it was affected by the N source, with higher CER in the nodulated plants. The greatest differences in CER, starch accumulation and leaf area were found between the nonsymbiotic plants and those with both endophytes. Statistical evaluations of leaf parameters for treatment or nutrient concentration (N and P) effects between the tri-partite and the nonsymbiotic treatments showed significant changes in concentration of P, but not N, with decreasing leaf age. Both endophytes apparently enhance CO(2) fixation at N and/or P concentrations lower than those of the nonsymbiotic plants. The effects of the endophytes on CO(2) fixation were additive.

Overexpression of low density lipoprotein (LDL) receptor eliminates LDL from plasma in transgenic mice

A complementary DNA encoding the human low density lipoprotein (LDL) receptor under control of the mouse metallothionein-I promoter was injected into fertilized mouse eggs, and a strain of mice expressing high levels of LDL receptors was established. After administration of cadmium, these mice cleared intravenously injected 125I-labeled LDL from blood eight to ten times more rapidly than did normal mice. The plasma concentrations of apoproteins B-100 and E, the two ligands for the LDL receptor, declined by more than 90 percent after cadmium treatment, but the concentration of another apoprotein, A-I, was unaffected. Therefore, overexpression of an endocytotic receptor can dramatically lower the ambient concentration of its ligand in vivo.

Sterol-dependent repression of low density lipoprotein receptor promoter mediated by 16-base pair sequence adjacent to binding site for transcription factor Sp1

A 42-base pair sequence from the 5' flanking region of the low density lipoprotein receptor gene was shown previously to confer sensitivity to sterol-mediated repression when inserted into the herpes simplex virus thymidine kinase promoter. This sequence contains two contiguous 16-base pair repeats, designated repeats 2 and 3, which differ from each other at four positions. In the current study we have analyzed separately the functions of repeats 2 and 3 by altering their sequences, inserting them into the -60 position of the thymidine kinase promoter, and introducing the hybrid promoters into hamster cells by transfection. These studies show that repeat 3 is a constitutive positive transcriptional element that acts in the absence or presence of sterols. Repeat 2 confers strong repression upon repeat 3 when sterols are present. In vitro DNase footprinting and gel retardation assays show that repeat 3, but not repeat 2, binds purified Sp1, a positive transcription factor. Mutants of repeat 3 that abolish transcriptional activity in vivo abolish Sp1 binding in vitro. We suggest that the low density lipoprotein receptor is regulated by a push-pull mechanism in which sterol-regulated binding of a protein to repeat 2 silences the activity of the adjacent Sp1-binding site in repeat 3.

Operator constitutive mutation of 3-hydroxy-3-methylglutaryl coenzyme A reductase promoter abolishes protein binding to sterol regulatory element

Through substitution mutagenesis we identified the promoter elements responsible for basal expression and sterol-mediated repression of transcription of the gene for 3-hydroxy-3-methylglutaryl coenzyme A reductase, a rate-controlling enzyme of cholesterol biosynthesis. Mutant promoters containing 277 base pairs (bp) of reductase 5' flanking sequence were inserted into recombinant plasmids upstream of the coding region for bacterial chloramphenicol acetyltransferase. The plasmids were transfected into hamster fibroblasts, and transcription was measured in the presence and absence of sterols. Mutations in three regions that are known to bind nuclear proteins markedly reduced transcription. Mutation of another protein-binding region of 20 bp in length did not reduce transcription, but it did abolish sterol-mediated repression, producing an operator constitutive phenotype. This mutation also abolished protein binding to the corresponding 20-bp region of DNA as determined by footprinting assays. When a DNA fragment containing these 20 bp was inserted into the herpes simplex virus thymidine kinase promoter, sterol-mediated repression was observed. This sequence contains an octanucleotide that shows a 7/8-bp match with a previously identified regulatory sequence in repeat 2 of the low density lipoprotein receptor promoter, another sterol-repressible gene. We hypothesize that this octanucleotide, GTGGCGGTG, is the core binding site for a sterol-dependent protein that represses transcription.

Multiple crm- mutations in familial hypercholesterolemia. Evidence for 13 alleles, including four deletions

The low density lipoprotein (LDL) receptors in fibroblasts from 132 subjects with the clinical syndrome of homozygous familial hypercholesterolemia were analyzed by immunoprecipitation with an anti-LDL receptor monoclonal antibody. 16 of the 132 cell strains (12%) synthesized no immunodetectable LDL receptor protein, indicating the presence of two mutant genes that failed to produce cross-reacting material (crm- mutations). DNA and mRNA from 15 of the 16 crm- patients, representing 30 crm- genes, were available for further study. Haplotype analysis based on 10 restriction fragment length polymorphisms (RFLPs) suggested that the 30 crm- genes represent 13 mutant alleles. Four of the alleles produced no mRNA. Three of these four mRNA- alleles had large deletions ranging from 6 to 20 kb that eliminated the promoter region of the gene. The fourth mRNA- allele did not contain any deletion or alteration in the promoter sequence; the reason for the mRNA- phenotype was not apparent. Nine alleles were positive for mRNAs, of which three encoded mRNAs of abnormal size. One of the abnormal mRNAs was produced by a gene harboring a deletion, and another was produced by a gene with a complex rearrangement. The third abnormal-sized mRNA (3.1 kb larger than normal) was produced by an allele that had no detectable alterations as judged by Southern blotting. The other six mRNA+ alleles appeared normal by Southern blotting and produced normal-sized mRNA but no receptor protein. The current studies demonstrate that mRNA analysis coupled with haplotype determination by Southern blot analysis can be used to classify crm- mutations at a genetic locus where multiple alleles exist.

Physiologic intracranial calcification with hyperintensity on MR imaging: case report and experimental model

CT and MR imaging showed basal ganglia calcification that appeared as high signal intensity on T1-weighted images of a patient with pseudohypoparathyroidism. MR imaging of an experimental model of calcium phosphate suspensions showed a signal similar to that seen in the patient. Additionally, T1 and T2 relaxation times of the solutions were measured and showed decreases in both parameters with increasing calcium phosphate concentrations. Intracranial calcification can appear as high signal intensity on T1-weighted images. An experimental model shows that the calcium salt decreases the T1 of surrounding water. Therefore, calcium, and possibly other elements, may induce paramagnetic susceptibility effects.

Spinal cord injury in newborns from use of umbilical artery catheters: report of two cases and a review of the literature

Umbilical artery catheter use in sick newborns has been associated with infarction of major organs such as the intestine and kidneys; spinal cord infarction has also been reported but is rare. We report two cases of spinal cord infarction and review the six others in the literature for preventable or predisposing conditions. Infusion of blood and hypertonic solutions, shock, and high position of the catheter tip were associated with infarction of the anterior spinal cord in these infants.

First cysteine-rich repeat in ligand-binding domain of low density lipoprotein receptor binds Ca2+ and monoclonal antibodies, but not lipoproteins

The ligand binding domain of the low density lipoprotein receptor consists of seven cysteine-rich repeats of approximately 40 amino acids each. These repeats, which are located at the NH2 terminus of the protein, are homologous to sequences in complement components C8 and C9. To determine the role of the first repeat (amino acids 2-42), we prepared two plasmids containing expressible low density lipoprotein receptor cDNAs. The first plasmid, p delta R1, lacks only the nucleotides encoding the first repeat. It produced a receptor that bound and internalized lipoproteins and recycled to the cell surface with the same efficiency as the normal receptor. This deleted receptor failed to bind two monoclonal antibodies, IgG-C7 and IgG-15C8, which were shown previously to react with the ligand-binding domain. The second plasmid, pR1, encodes a markedly truncated protein whose extracellular domain consists of the first repeat joined to the transmembrane and cytoplasmic domains. This protein bound the two monoclonal antibodies with the same affinity as the normal receptor, but failed to bind lipoproteins. Binding of IgG-15C8 to the normal receptor and the pR1-encoded protein was Ca2+-dependent, indicating that the first repeat binds Ca2+. We conclude that repeats 2-6 in the ligand-binding domain are sufficient for binding lipoproteins and that the first repeat is highly immunogenic, but is not required for lipoprotein binding.

Self-association of the low density lipoprotein receptor mediated by the cytoplasmic domain

When the low density lipoprotein (LDL) receptor was solubilized from bovine adrenal cortex membranes and subjected to electrophoresis in the absence of reducing agents, a disulfide-bonded dimeric species was demonstrated. Formation of these covalent bonds was blocked when the tissue was homogenized in the presence of sulfhydryl alkylating agents, indicating that the native receptor was self-associated noncovalently and that the disulfide bond formation occurred only after homogenization. The disulfide-linked dimers were disrupted and the receptor was restored to a monomeric form when inside-out adrenal vesicles were treated with trypsin, suggesting that the disulfide bond formation involved the 50-amino acid cytoplasmic domain of the receptor. When the receptor was solubilized from bovine adrenal cortex membranes and then purified by ion exchange and affinity chromatography, it could be covalently coupled into dimers and trimers in the presence of bivalent cross-linking agents. Receptor dimers could also be demonstrated by chemical cross-linking of intact cells that were transfected with an expressible cDNA encoding the normal human LDL receptor. Dimer formation was markedly reduced in transfected cells expressing mutated cDNAs that had premature termination codons at positions 792, 807, and 812, which produced shortened receptors that retained 2, 17, and 22 of the original 50 amino acids of the cytoplasmic domain, respectively. The first two mutant receptors, which did not form oligomers, did not enter coated pits and were not rapidly internalized by cells. However, the mutant receptor that terminates at position 812 was internalized normally even though oligomer formation was greatly reduced. Moreover, a mutant receptor with a cysteine substituted for a tyrosine at position 807, which internalized very slowly, showed a normal susceptibility to chemical cross-linking. Deletion of external domains of the LDL receptor, including the epidermal growth factor homology region and the O-linked sugar domain, did not alter susceptibility to chemical cross-linking. We conclude that the cytoplasmic domain of the LDL receptor is responsible both for self-association into oligomers and for clustering in coated pits, but the available data do not establish a causal connection between these two events.