Anti-Ro autoantibodies, found in sera of patients with systemic lupus erythematosus, Sjogren's syndrome, and related diseases, target the Ro ribonucleoprotein particles (RNPs). Although the polypeptide and RNA components of the Ro RNPs have been characterized, much less is known about the native structure of these particles. We have now characterized by biochemical techniques intact Ro ribonucleoprotein particles from cultured HeLa cells. These particles segregated in three discrete subpopulations with characteristic physicochemical properties: one containing hY5 RNA (RohY5 particles), one containing only hY4 RNA (RohY4 particles) and one with hY1, hY3, and hY4 RNAs (RohY1-hY4 particles). The RohY5 particles were purified free of contaminating ribonucleoproteins; both the La and the 60-kD Ro polypeptides were stable components of this portion of the Ro RNPs. The La RNPs co-purified with the RohY4 particles and contaminated the RohY1-hY4 RNPs. The stable association between the La and the 60-kD Ro polypeptides provides a potential macromolecular target for the linked set of anti-Ro and anti-La antibodies, and suggests a possible functional association of these polypeptides.
G Boire, J Craft
We studied the effect of the orientation of the 7-hydroxyl group in taurocholate (7 alpha) and tauroursocholate (7 beta) on the feedback regulation of bile-acid synthesis and its rate-controlling enzyme, cholesterol 7 alpha-hydroxylase, in bile-fistula rats. To ensure a constant supply of cholesterol and to label newly synthesized bile acids, RS[2-14C]mevalonolactone was infused intraduodenally at 154 mumol/h before and during bile-acid infusion. Mevalonolactone inhibited hydroxymethyl-glutaryl CoA reductase activity 90% but did not increase bile-acid synthesis and cholesterol 7 alpha-hydroxylase activity. When sodium taurocholate was infused at the rate of 27 mumol/100 g rat per h (equivalent to the hourly hepatic bile-acid flux), bile-acid synthesis decreased 82% and cholesterol 7 alpha-hydroxylase activity declined 78%. This inhibitory effect was observed in the absence of hepatic damage. In contrast, sodium tauroursocholate infused at the same rate did not decrease bile-acid synthesis nor cholesterol 7 alpha-hydroxylase activity. Hepatic cholesterol content rose 36% with sodium taurocholate but did not change during sodium tauroursocholate administration. These results demonstrate that the feedback inhibition of bile-acid synthesis is mediated through the regulation of cholesterol 7 alpha-hydroxylase. In these experiments, taurocholate was a far more potent inhibitor than its 7 beta-hydroxy epimer, tauroursocholate.
S Shefer, L Nguyen, G Salen, A K Batta, D Brooker, F G Zaki, I Rani, G S Tint
The functional heterogeneity of uridine diphosphate-glucuronosyltransferase (UDPGT) and its deficiency in human liver were investigated. The monoclonal antibody (MAb) WP1, which inhibits bilirubin and phenol-glucuronidating activity, was used to immunopurify UDPGTs from human liver. Purified UDPGTs were injected into mice to obtain new MAbs. Immunoblotting of microsomes with MAb HEB7 revealed at least three polypeptides in liver (56, 54, and 53 kD) and one in kidney (54 kD). In liver microsomes from four patients (A, B, C, and D) with Crigler-Najjar syndrome type I (CN type I), UDPGT activity towards bilirubin was undetectable (A, B, C, and D) and activity towards phenolic compounds and 5-hydroxytryptamine either reduced (A and B) or normal (C and D). UDPGT activity toward steroids was normal. Immunoblot studies revealed that the monoclonal antibody WP1 recognized two polypeptides (56 and 54 kD) in liver microsomes from patient A and none in patient B. With HEB7 no immunoreactive polypeptides were seen in these two patients. Patient C showed a normal banding pattern and in patient D only the 53-kD band showed decreased intensity. These findings suggest considerable heterogeneity with regard to the expression of UDPGT isoenzymes among CN type I patients.
H H van Es, B G Goldhoorn, M Paul-Abrahamse, R P Elferink, P L Jansen
Cardiac hypertrophy produced in vivo by pressure overload is characterized by selective up-regulation of the fetal/neonatal beta-cardiac myosin heavy chain (MHC) isogene. However, a molecular signal for beta-MHC isogene induction has not been identified. We examined cardiac MHC isogene expression in a cell culture model for hypertrophy. alpha-MHC and beta-MHC iso-protein and iso-mRNA levels in cultured cardiac myocytes were quantified during hypertrophy stimulated by the alpha 1-adrenergic agonist, norepinephrine (NE). beta-MHC iso-protein content was increased 3.2-fold vs. control (P less than 0.001), whereas alpha-MHC isoprotein content was not changed significantly (1.4-fold vs. control, P = NS). MHC iso-mRNA levels were quantified by nuclease S1 analysis, using a single oligonucleotide probe. NE increased beta-MHC iso-mRNA content by 3.9-fold vs. control (P less than 0.001), but there was no change in alpha-MHC iso-mRNA (1.1-fold vs. control, P = NS). The NE-stimulated increase in beta-MHC iso-mRNA preceded in time the increase in beta-MHC isoprotein accumulation. The EC50 for NE induction of beta-MHC was 40 nM, and pharmacologic experiments indicated alpha 1-adrenergic receptor specificity. alpha-MHC isogene expression was predominant in control myocytes (68% alpha-isoprotein and 60% alpha-iso-mRNA). In contrast, beta-MHC expression was equal to alpha-MHC or predominant after treatment with NE (51% beta-isoprotein and 69% beta-iso-mRNA). Thus, alpha 1-adrenergic receptor stimulation increases the cellular contents of beta-MHC iso-mRNA and beta-MHC isoprotein during hypertrophy of cultured neonatal rat cardiac myocytes, but does not change the levels of alpha-MHC iso-mRNA or isoprotein. The effect on beta-MHC is mediated primarily at the level of mRNA steady-state level (pretranslational). Activation of the alpha 1-adrenergic receptor is the first identified molecular signal for increased beta-MHC isogene expression in a model of cardiac hypertrophy.
L E Waspe, C P Ordahl, P C Simpson
C1- inhibitor (C1(-)-Inh) catabolism in plasma of patients with hereditary angioneurotic edema (HANE) was assessed by measuring the complexes formed by C1(-)-Inh with its target proteases (C1-s, Factor XIIa, and kallikrein) and a modified (cleaved) inactive form of C1(-)-Inh (iC1(-)-Inh). This study was performed in plasma from 18 healthy subjects and 30 patients with HANE in remission: 20 with low antigen concentration (type I) and 10 (from 5 different kindreds) with dysfunctional protein (type II). Both type-I and type-II patients had increased C1(-)-C1(-)-Inh complexes (P less than 0.0001), which in type I inversely correlated with the levels of C1(-)-Inh (P less than 0.001). iC1(-)-Inh was normal in all type-I patients and in type-II patients from three families with increased C1(-)-Inh antigen, whereas iC1(-)-Inh was higher than 20 times the normal values in patients from the remaining two families with C1(-)-Inh antigen in the normal range. None of the subjects had an increase of either Factor XIIa-C1(-)-Inh or kallikrein-C1(-)-Inh complexes. This study shows that the hypercatabolism of C1(-)-Inh in HANE patients at least in part occurs via the formation of complexes with C1- and that genetically determined differences in catabolism of dysfunctional C1(-)-Inh proteins are present in type-II patients.
M Cugno, J Nuijens, E Hack, A Eerenberg, D Frangi, A Agostoni, M Cicardi
Gastric lipase, pancreatic colipase-dependent lipase, and bile salt-stimulated lipase all have potential roles in digestion of human milk triacylglycerol. To reveal the function of each lipase, an in vitro study was carried out with purified lipases and cofactors, and with human milk as substrate. Conditions were chosen to resemble those of the physiologic environment in the gastrointestinal tract of breast-fed infants. Gastric lipase was unique in its ability to initiate hydrolysis of milk triacylglycerol. Activated bile salt-stimulated lipase could not on its own hydrolyze native milk fat globule triacylglycerol, whereas a limited hydrolysis by gastric lipase triggered hydrolysis by bile salt-stimulated lipase. Gastric lipase and colipase-dependent lipase, in combination, hydrolyzed about two thirds of total ester bonds, with monoacylglycerol and fatty acids being the end products. Addition of bile salt-stimulated lipase resulted in hydrolysis also of monoacylglycerol. When acting together with colipase-dependent lipase, bile salt-stimulated lipase contributed also to digestion of tri- and diacylglycerol. We conclude that digestion of human milk triacylglycerol depends on three lipases with unique, only partly overlapping, functions. Their concerted action results in complete digestion with free glycerol and fatty acids as final products.
S Bernbäck, L Bläckberg, O Hernell
Immediate hypersensitivity is due to the release of mediators from mast cells and basophils after the crosslinking of Fc epsilon RI. The appearance of such receptors was examined during differentiation of human and mouse bone marrow cells cultured in the presence of IL-3. As already reported, mouse bone marrow yield cultures of greater than 95% mast cells by 3 wk, whereas human bone marrow develop into cultures comprising 25% basophils by 3 wk. Here we show that transcripts for Fc epsilon RI subunits and membrane-associated receptors are apparent by 1 wk in both human and murine IL-3-dependent bone marrow cells. These cells contain few, if any, granules. The expression of transcripts and the number of receptor-positive cells continue to increase over 3 wk of culture. In parallel, a progressively larger number of cells become increasingly granulated to finally resemble either basophils or mast cells. Mature peripheral human basophils also contain transcripts for Fc epsilon RI and, therefore, may have the potential to synthesize de novo receptors. The early appearance of Fc epsilon FI during cell differentiation may be important for these cells to respond to IgE-mediated stimuli before granulation. The physiologic role of Fc epsilon RI could be to mediate lymphokine production (IL-3, IL-4, IL-6, and granulocyte/macrophage colony-stimulating factor) without inducing cellular degranulation.
H L Thompson, D D Metcalfe, J P Kinet
The effects of homologous plasma HDL and VHDL fractions on established atherosclerotic lesions were studied in cholesterol-fed rabbits. Atherosclerosis was induced by feeding the animals a 0.5% cholesterol-rich diet for 60 d (group 1). Another group of animals were maintained on the same diet for 90 d (group 2). A third group was also fed the same diet for 90 d but received 50 mg HDL-VHDL protein per wk (isolated from normolipemic rabbit plasma) during the last 30 d (group 3). Aortic atherosclerotic involvement at the completion of the study was 34 +/- 4% in group 1, 38.8 +/- 5% in group 2, and 17.8 +/- 4% in group 3 (P less than 0.005). Aortic lipid deposition was also significantly reduced in group 3 compared with group 1 (studied at only 60 d) and group 2. This is the first in vivo, prospective evidence of the antiatherogenic effect of HDL-VHDL against preexisting atherosclerosis. Our results showed that HDL plasma fractions were able to induce regression of established aortic fatty streaks and lipid deposits. Our results suggest that it may be possible not only to inhibit progression but even to reduce established atherosclerotic lesions by HDL administration.
J J Badimon, L Badimon, V Fuster
To date, testing of various cytokines for the stimulation of blood cell production has not demonstrated a consistent effect on peripheral platelet levels. In this report, we provide evidence that human recombinant IL-6 increased platelet production in mice, as measured by both peripheral platelet levels and [75Se]selenomethionine (75SeM) incorporation into newly forming platelets. Peripheral white blood cell counts also were increased, but only to a modest extent, and hematocrit values were unchanged. A dose-response relationship between the amount of IL-6 administered and platelet count, 75SeM incorporation, and white blood cell count was demonstrated. Detectable megakaryocyte and granulocyte-macrophage colony-forming cells in mice that had received IL-6 also were increased in both bone marrow and spleen. These results demonstrate the ability of a purified, recombinant protein to stimulate platelet production in vivo.
R J Hill, M K Warren, J Levin
We have investigated S. aureus adherence to human endothelial cells utilizing an in vitro model. Staphylococcus binding to confluent endothelial cell monolayers was saturable in both dose and time response studies suggesting that the binding interaction was specific. We have developed a technique, based on the pH dependent affinity of iminobiotin for streptavidin, for the isolation of an endothelial cell membrane component that binds S. aureus, in vitro. A 50-kD membrane component was isolated and purified using this approach. This component was trypsin sensitive, periodate insensitive, and did not label with [3H]glucosamine. [35S]Methionine and [125I]iodine labeling confirmed that the protein was synthesized by and expressed on the endothelial cell surface. Functional binding studies demonstrated that staphylococci, but not endothelial cells, bound to the protein when immobilized on microtiter wells. Preincubation of staphylococci with the purified protein significantly (P less than 0.001) reduced staphylococcal binding to cultured endothelial cells. The capacity of S. aureus to colonize and invade endovascular surfaces may in part be a consequence of staphylococcal interaction with this endothelial cell membrane protein.
D C Tompkins, V B Hatcher, D Patel, G A Orr, L L Higgins, F D Lowy
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