Relationship between invariant chain expression and major histocompatibility complex class II transport into early and late endocytic compartments.

Invariant chain (Ii), which associates with major histocompatibility complex (MHC) class II molecules in the endoplasmic reticulum, contains a targeting signal for transport to intracellular vesicles in the endocytic pathway. The characteristics of the target vesicles and the relationship between Ii structure and class II localization in distinct endosomal subcompartments have not been well defined. We demonstrate here that in transiently transfected COS cells expressing high levels of the p31 or p41 forms of Ii, uncleaved Ii is transported to and accumulates in transferrin-accessible (early) endosomes. Coexpressed MHC class II is also found in this same compartment. These early endosomes show altered morphology and a slower rate of content movement to later parts of the endocytic pathway. At more moderate levels of Ii expression, or after removal of a highly conserved region in the cytoplasmic tail of Ii, coexpressed class II molecules are found primarily in vesicles with the characteristics of late endosomes/prelysosomes. The Ii chains in these late endocytic vesicles have undergone proteolytic cleavage in the lumenal region postulated to control MHC class II peptide binding. These data indicate that the association of class II with Ii results in initial movement to early endosomes. At high levels of Ii expression, egress to later endocytic compartments is delayed and class II-Ii complexes accumulate together with endocytosed material. At lower levels of Ii expression, class II-Ii complexes are found primarily in late endosomes/prelysosomes. These data provide evidence that the route of class II transport to the site of antigen processing and loading involves movement through early endosomes to late endosomes/prelysosomes. Our results also reveal an unexpected ability of intact Ii to modify the structure and function of the early endosomal compartment, which may play a role in regulating this processing pathway.

Toll-like receptor 2 (P631H) mutant impairs membrane internalization and is a dominant negative allele.

We have sequenced 416 Toll-like receptor-2 (TLR2) alleles in 208 subjects in a tuberculosis case-control study in Croatian Caucasian population. We found ten single nucleotide polymorphisms (SNP) among which three were novel (S97S, T138I and L266F). The genotype containing TLR2-P631H SNP was significantly overrepresented in patients with tuberculosis when compared to contact controls, suggesting a small yet increased risk to disease. The causative agent of tuberculosis is Mycobacterium tuberculosis, which can bind to TLR2 with its lipoprotein coat. The TLR2-P631H mutant has a dominant negative effect on the wild type TLR2 signalling in transfected HEK293 kidney cells using the NF-kappaB-driven luciferase as a reporter gene with ligands like M. avium extracts, Pam3CysSK4 or FSL-1 that bind TLR2/TLR1 or TLR2/TLR6 heterodimers, respectively. Studies on internalization from the Regular Madine Darby Canine Kidney cell surface into the early endosomal compartments showed a lower rate of the mutant compared to the wild type. Our data, in combination with a report by others show that the TLR2-P631H allele could be associated with protection to meningococcal meningitis, suggest that by dominantly inhibiting the response of cells important in the immune response this mutant might confer either protection or susceptibility to meningitis or tuberculosis, respectively.

MHC II and the endocytic pathway: regulation by invariant chain.

The major histocompatibility complex (MHC) class I and II molecules perform vital functions in innate and adaptive immune responses towards invading pathogens. MHC class I molecules load peptides in the endoplasmatic reticulum (ER) and display them to the T cell receptors (TcR) on CD8(+) T lymphocytes. MHC class II molecules (MHC II) acquire their peptides in endosomes and present these to the TcR on CD4+ T lymphocytes. They are vital for the generation of humoral immune responses. MHC II assembly in the ER and trafficking to endosomes is guided by a specialized MHC II chaperone termed the invariant chain (Ii). Ii self-associates into a trimer in the ER, this provides a scaffold for the assembly of three MHC II heterodimers and blocks their peptide binding grooves, thereby avoiding premature peptide binding. Ii then transports the nascent MHC II to more or less specialized compartment where they can load peptides derived from internalized pathogens.

Targeting of membrane proteins to endosomes and lysosomes.

The pathways involved in targeting membrane proteins to lysosomes are extraordinarily complex. Newly synthesized proteins in the ER are transported to the Golgi complex, and upon arrival at the trans Golgi network (TGN) are targeted either directly to endosomes, or first to the cell surface from where they can be rapidly internalized into the endocytic pathway for delivery to lysosomes. The routes to endosomes are specified by sorting motifs in the cytoplasmic tails of the proteins that are recognized at the TGN or plasma membrane. The molecular details of these processes are just emerging.

Intracellular transport and localization of major histocompatibility complex class II molecules and associated invariant chain.

The intracellular transport and location of major histocompatibility complex (MHC) class II molecules and associated invariant chain (Ii) were investigated in a human melanoma cell line. In contrast to the class II molecules, which remain stable for greater than 4 h after synthesis, the associated Ii is proteolytically processed within 2 h. During or shortly after synthesis the NH2-terminal cytoplasmic and membrane-spanning segment is in some of the Ii molecules cleaved off; during intracellular transport, class II associated and membrane integrated Ii is processed from its COOH terminus in distinct steps in endocytic compartments. Immunocytochemical studies at the light and electron microscopic level revealed the presence of class II molecules, but not of Ii on the cell surface. Intracellularly both Ii and class II molecules were localized in three morphologically and kinetically distinct compartments, early endosomes, multivesicular bodies, and prelysosomes. This localization in several distinct endosomal compartments contrasts with the localization of class II molecules in mainly one endocytic compartment in B lymphoblastoid cell lines. As in these lymphoblastoid cell lines Ii is known to be rapidly degraded it is conceivable that the rate of proteolysis of the class II associated Ii and its dissociation from class II molecules modulates the retention of the oligomeric complex in endocytic compartments, and as a consequence the steady-state distribution of these molecules within the endosomal system.

Mitotic partitioning of endosomes and lysosomes.

BACKGROUND: Some of the mechanisms underlying cell division and partitioning of the cellular components into the daughter cells are well known. Within the endomembrane system, there is a general cessation of membrane traffic, including endocytosis and endosome fusion, at the onset of mitosis. However, the fate of endosomes and lysosomes during mitosis has been less well studied. RESULTS: Using video and confocal microscopy of living cells, we show here that endosomes and lysosomes remain intact and separate during mitosis. The segregation into daughter cells takes place by coordinated movements, and during cytokinesis, these organelles accumulate in the vicinity of the microtubule organization center. However, partitioning into daughter cells is not more accurate than a calculated stochastic distribution, despite the apparent order to the process. CONCLUSION: We conclude that partitioning of endosomes and lysosomes is an ordered, yet imprecise, process, and that the organelle copy number is maintained by the daughter cells.

A new triple-stranded alpha-helical bundle in solution: the assembling of the cytosolic tail of MHC-associated invariant chain.

BACKGROUND: The invariant chain (li) is a transmembrane protein that associates with the major histocompatibility complex class II (MHC II) molecules in the endoplasmic reticulum. The cytosolic tail of li contains two leucine-based sorting motifs and is involved in sorting the MHC II molecules to the endosomal pathway where the peptide antigen is bound. This region of li also contributes to phenotypical changes in cells, such as the formation of large endocytic structures. RESULTS: We report here the three-dimensional structure of a 27 amino acid peptide corresponding to the cytosolic tail of li. The structure was determined by nuclear magnetic resonance (NMR) spectroscopy using a computational strategy. At high concentration, this structure reveals a new triple-stranded alpha-helical bundle in which the helices, two parallel and one antiparallel, are almost coplanar. Trimerization is mediated by electrostatic interactions intercalated by three hydrophobic layers. CONCLUSIONS: The new trimer fold, the first to be identified by NMR data alone, can be used to improve understanding of protein-protein interactions and to model multiple-helical transmembrane proteins and receptors. We suggest that interactions of the li cytosolic tails may form part of a mechanism that could cause the endosomal retention and enlarged endosomes induced by li.

Antagonistic effect of glucocorticoids on retinoic acid induced growth inhibition and morphological alterations of a human cell line.

When the human cell line NHIK 3025 was exposed to retinoic acid (1 nM; 10 microM), the cell cycle time was prolonged. Experiments using cells synchronized by mitotic selection showed that the retinoic acid induced growth delay was barely seen within the first cell cycle after exposure to 10 microM retinoic acid, whereas the next cell cycle durations were increased 30-60%. The effect was reversible as normal growth rate was restored after removal of the drug. DNA histograms indicated a prolongation of G1 of the cell cycle. We have shown earlier that glucocorticoid steroids also induce a prolongation of the cell cycle, located within G1. When the cells were exposed to the synthetic glucocorticoid, dexamethasone, in addition to retinoic acid, no additive effect was found; on the contrary, growth inhibition was less than that with retinoic acid alone. Dexamethasone from 1 nM upwards antagonized the growth inhibitory effect of retinoic acid. This glucocorticoid mediated effect seemed to be mediated via the glucocorticoid receptor, as no effect was seen when the receptor was blocked by the antagonist 17 beta hydroxy-11 beta, 4-dimethylaminophenyl-17 alpha-propynyl estra 4,9 diene-3-one [RU 38486]. The growth inhibition studies were supported by morphological observations showing that dexamethasone induced cytoskeletal alterations dominated when the cells were exposed to both drugs simultaneously. These findings might be of importance in cancer therapy where both drugs are used.

The leucine-based motif DDQxxLI is recognized both for internalization and basolateral sorting of invariant chain in MDCK cells.

The major histocompatibility complex (MHC) class II-associated invariant chain (Ii) contains signals for transport to endocytic compartments where the class II molecules bind antigenic peptides for presentation to CD4+ T cells. Two leucine-based signals in the Ii cytoplasmic tail can be independently recognized for endosomal sorting of Ii, and we have recently shown that each signal is sufficient for basolateral sorting and internalization of Ii in polarized Madine Darby Canine Kidney (MDCK) II cells. The recognition motif for endosomal sorting is complex and consists of two critical leucine-like residues as well as surrounding amino acids. Here, we have analyzed the importance of residues surrounding the membrane-distal leucine-based signal in basolateral sorting and internalization of Ii in MDCK II cells. We find that the DDQxxLI motif is involved in both sorting events indicating the presence of similar signal recognition components both at the TGN and at the plasma membrane. The identical motif is required for endosomal localization and internalization of Ii also in simian COS cells and the human HeLa and M1 cells.

Intracellular localization of the glucocorticoid receptor: evidence for cytoplasmic and nuclear localization.

Using a monospecific, monoclonal antibody against the glucocorticoid receptor (GR), an immunocytochemical study was performed to investigate the intracellular localization of GR both in the presence or absence of ligand. With all fixation methods tested (paraformaldehyde, acetic acid in ethanol, Bouin's fixative, and bensochinone in PBS), it was possible to obtain specific GR staining. Fixation with paraformaldehyde was chosen for further studies on the effect of permeabilization, using several concentrations of Triton X-100 or saponin. A rat Rueber hepatoma (H-4-II-E) and a human uterus carcinoma (NHIK 3025) cell line were used as well as cultured hepatocytes from normal rat. The accessibility of the different cell compartments after fixation and permeabilization was tested for by using antibodies against cellular constituents with known locations (i.e. core-nucleosome proteins and tubulin), in combination with the anti-GR antibody in double immunofluorescence staining experiments. The specific GR stain obtained with the indirect peroxidase antiperoxidase technique or with fluorescein isothiocyanate-labeled second antibodies was shown to be present both in the cytoplasm and in the nucleus. Staining of all cellular compartments was abolished (peroxidase antiperoxidase) or diminished (fluorescein isothiocyanate) if the monoclonal antibody was preincubated with a 90% pure GR preparation. These findings are in contrast to recently reported immunocytochemical studies, where a strict nuclear existence of the estrogen and progestin receptors has been reported. Consequently, generalizations with regard to steroid receptor localization cannot be made. Furthermore, an in vitro model is described, where the effect of dexamethasone administration upon the localization of receptor staining in H-4-II-E cells can be studied.

Effect of aminoglutethimide on antipyrine, theophylline, and digitoxin disposition in breast cancer.

The influence of aminoglutethimide (AG) on antipyrine, theophylline, and digitoxin kinetics was examined. Antipyrine was given as a single test dose before and after 3 mo of AG treatment, whereas theophylline and digitoxin kinetics were investigated at steady state in patients receiving these drugs therapeutically before and after AG therapy. During AG treatment, mean clearance rates for antipyrine, theophylline, and digitoxin increased by 81%, 32%, and 109%. Together with earlier reports of effects of AG on warfarin and dexamethasone disposition and on its own metabolism, these findings indicate that AG is a potent inducer of drug metabolizing microsomal monooxygenases of the liver. Since many drugs known to be metabolized by this enzyme system are frequently used for concomitant conditions in patients with breast cancer, interactions with AG are to be expected.

Drug discontinuations in the United Kingdom and the United States, 1964 to 1983: issues of safety.

Since the modern era of drug regulation began in the early 1960s, fewer new drugs have been approved for marketing in the United States than in the United Kingdom. We examined whether information can be obtained about the relative safety of higher and lower introductory rate policies by comparing each country's record of drugs that have been discontinued (removed from the market, withdrawn, or whose licenses were allowed to lapse) while a question of safety existed. We have compiled a list of both older (approved before 1964) and newer (approved in 1964 or later) chemical entities discontinued in the last two decades. With the aforementioned broad criteria to define "discontinuation," and to assess whether a question of safety was involved, our study showed that a total of 24 chemical entities have been discontinued in the United States or the United Kingdom. Nearly half (10 drugs) were products that had been approved in both countries, while the remainder (drugs that had been exclusively available in one country or the other) consisted of four drugs in the United States and 10 in the United Kingdom. Among the drugs introduced during the last two decades, five have been discontinued in the United States and eight in the United Kingdom. Each country's record of discontinuations has been remarkably similar for drugs introduced after 1974: Four have been discontinued in the United States and three in the United Kingdom. Since drugs discontinued while a safety question existed represent only 2% of the new chemical entities introduced, it appears that drugs that reach the market under the prevailing regulatory systems are seldom associated with unacceptable toxicity.

Transplacental passage of diazepam during labor: influence of uterine contractions.

The rate of transplacental passage of diazepam (DZ) has been studied in 33 cases of cephalic presentation where operative forceps delivery was indicated by intrauterine hypoxia or by prolonged second stage of labor. The drug (30 mg) was injected intravenously immediately before delivery either during uterine contractions (Group I) or in the relaxation period (Group II) according to a randomized protocol. As judged by the concentration in the newborn and the child/mother concentration ratio at 2 hr after delivery, and the concentration on the second day, the fetal exposure to the drug was probably less when the injection was timed to coincide with uterine contractions. In the group of patients given the drug in the relaxation period, the injection-delivery (I-D) interval was up to 305 sec and the 2-hr child/mother concentration ratio was close to unity in some cases. It therefore appears that the transplacental passage of DZ is rapid when the high initial concentrations in the maternal circulation coincide with favorable conditions for transfer in the relaxation period. Although sleep was induced by the injection of DZ in all of the mothers, the amounts of drug transferred during the short I-D intervals in the present study did not exert delterious effects on the newborn infants.

Drug safety discontinuations in the United Kingdom, the United States, and Spain from 1974 through 1993: a regulatory perspective.

The objective of the present study was to compare the number of new chemical entities (NCEs) and new biologicals entities (NBEs) approved for marketing during the period 1974 through 1993 in the United Kingdom, the United States, and Spain that were subsequently discontinued (removed from the market, withdrawn, or whose license was allowed to lapse) while a question of safety existed. Of the products approved during the two decades of the study period, a total of 29 drugs were subsequently discontinued for safety reasons in at least one of the three countries (United Kingdom: 20 safety discontinuations; United States: 10; and Spain: 16). These represent 3% to 4% of all drugs introduced in these countries, an increase compared to the period from 1964 through 1983, when approximately 2% of all NCEs were discontinued for safety reasons. The therapeutic classes most commonly associated with safety discontinuations were the nonsteroidal anti-inflammatory drugs (nine drugs), vasodilators (four drugs), and antidepressants (three drugs). U.S. companies or their foreign subsidiaries were involved as originators (patent-holders and/or developers) of approximately 40% of the drugs discontinued for safety reasons.

The bio-logical role of invariant chain (Ii) in MHC class II antigen presentation.

Foreign antigens are internalized by antigen presenting cells by endocytosis and processed to peptides. To enable presentation of antigenic peptides by MHC class II molecules, these molecules have to be sorted to endosomal compartments where they can meet and bind the peptides. Invariant chain is complexed with MHC class II molecules and contains sorting signals responsible for MHC class II accumulation in endosomes. Invariant chain also has several other features contributing to the immune system's specific combat against invaders.

Time-course of transplacental passage of diazepam: Influence of injection-delivery interval on neonatal drug concentrations.

Neonatal drug concentrations and neonate/mother concentration ratios are reported in 73 cases of elective Caesarean section and forceps deliveries where diazepam was used as an intravenous sleep-inducing agent. The various parameters were plotted against the injection-delivery interval and the correlation was tested using a non-parametric ranking method. The concentration of diazepam in mixed arteriovenous umbilical cord blood was negatively correlated with the injection-delivery interval in the range of 55 to 810 seconds. Statistically significant positive correlation (p less than 0.001) were found between the injection-delivery interval and the neonatal concentrations at 2 and 24 hours. The corresponding neonate/mother concentration ratios varied considerably, and were not so strongly correlated to the duration of antenatal drug transfer. The results suggest that with a slowly eliminated agent like diazepam, the drug concentration in capillary blood obtained from the newborn a few hours after delivery gives a reasonably good indication of the fetal drug exposure. The transplacental passage of diazepam is rapid, with distribution equilibrium between mother and fetus approached within 5 to 10 minutes after intravenous injection of the drug.

Induction of peroxisomal enzymes and palmitoyl-CoA hydrolase in rats treated with cholestyramine and nicotinic acid.

Male Wistar rats were given 200 mg/kg/day nicotinic acid or 1000 mg/kg/day cholestyramine by stomach tube for ten days. Peroxisomal palmitoyl-CoA oxidation (cyanide-insensitive) and the activities of palmitoyl-CoA hydrolase and urate oxidase were significantly increased in the total liver homogenate. Subcellular fractionation showed enhanced enzyme activities after drug treatment mainly in the peroxisome-containing fractions. The increase in urate oxidase activity and its subcellular distribution suggest that the tested drugs induce core-containing peroxisomes. The findings are similar to those previously reported with low doses of peroxisome-proliferating hypolipidemic drugs and with acetylsalicylic acid, a drug which is structurally similar to nicotinic acid. Since cholestyramine is not absorbed, its influence on hepatic enzymes probably occurs indirectly as a consequence of enhanced catabolism of cholesterol.

Effect of oral high-dose progestins on the disposition of antipyrine, digitoxin, and warfarin in patients with advanced breast cancer.

The influence of two progestins, medroxyprogesterone acetate (MPA) and megestrol acetate (MA), given orally in high doses, on the pharmacokinetics of antipyrine, digitoxin, and warfarin were studied in patients with advanced breast cancer. Antipyrine and warfarin were given as a single test dose before and after 5 weeks of progestin treatment. The pharmacokinetics of digitoxin was investigated at steady state in patients receiving this drug therapeutically before and during treatment with progestins. Small changes in clearance rates for antipyrine, warfarin, and digitoxin were found. A minor decrease observed in warfarin clearance however may be of clinical importance. Half-lives decreased by 13% for antipyrine and increased by 71% for warfarin. High-dose progestins given orally do not seem to have a major influence on drug metabolism, probably reflecting a minor effect on drug and steroid-metabolizing microsomal mono-oxygenases in the liver.

Effects of potassium dichromate on the cell cycle of an established human cell line (NHIK 3025).

The effect of K2Cr2O7 exposure on the cell cycle phases of the human cell line NHIK 3025 has been studied. Inhibition of cell proliferation was found to depend on the concentration and length of exposure. An effect on cell proliferation was observed 6-9 h after addition of K2Cr2O7, whereas cell death was not observed until 3-4 days later. The cells were most sensitive in G2 phase. After exposure to 8 mumol/l K2Cr2O7 the greatest prolongation of the cell cycle was in G2 + M phase, but an increase of S phase was also observed. No prolongation of G1 phase could be measured. Our results thus indicate that K2Cr2O7 delays progression through the cell cycle.

The absorption and elimination of metoclopramide in three animal species.

The absorption and elimination of metoclopramide have been studied in the rat, rabbit and dog. Thin-layer chromatography followed by photodensitometry was used for the analysis of the unchanged drug and its metabolites. N-De-ethylation is an important Phase I metabolic reaction and conjugation with glucoronic acid and sulphate is a major route of metabolism, particularly in the rabbit. The pharmacokinetic parameters after intravenous administration showed little interspecies variation. First order elimination kinetics with short half-lives and high apparent volumes of distribution (greater than 1.1 kg(-1)) were observed. Major interspecies variations were seen after oral administration of high doses of the drug. Metoclopramide was eliminated slowly after oral administration to rats. The findings in the rabbit and in the dog suggest that the liver plays an active role reducing the systemic availability of unchanged metoclopramide after oral administration.