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At least 613 records · Page 34Linked to original sources
PubMed2005

Etiology of primary biliary cirrhosis: the search for the culprit.

Primary biliary cirrhosis (PBC) is an organ-specific autoimmune disease characterized by the presence of high titer antimitochondrial autoantibodies (AMAs) and destruction of intrahepatic small bile ducts. Despite vigorous efforts in the characterization of autoantibodies and bile duct histopathology, the etiology of this disease is unclear. Although there is no correlation between the titer of AMAs and disease severity, the presence of AMAs usually occurs before symptoms of liver abnormalities. We believe that the production of AMAs is not an epiphenomenon, and an understanding of the mechanism of AMA induction will shed light on the etiology of PBC. Recent studies have suggested that the induction of PBC is multifactorial, in which the primary player involves the xenobiotics modification of mitochondrial proteins or exposure to xenobiotic-modified bacterial mitochondrial protein homologs, leading to breaking of tolerance to the human mitochondrial autoantigens and eventually liver pathology in genetic susceptible individuals. We discuss the immunophysiological characteristics of biliary epithelial cells, biochemistry of the 2-oxo-acid dehydrogenase complex, and environmental and genetic factors relevant to PBC.

Antibody Formation↗
PubMed1982

Induction of Flavonoid Synthesizing Enzymes by Light in Etiolated Pea (Pisum sativum cv. Midfreezer) Seedlings.

Etiolated pea (Pisum sativum cv. Midfreezer) seedlings respond to illumination with white light by changes in the activity of phenylpropanoid and flavonoid synthesizing enzymes. Unlike in cell cultures, changes in enzyme activity in pea seedlings are not concerted. Phenylalanine ammonia-lyase (EC 4.3.1.5) activity peaked approximately 18 hours after onset of illumination. The phenylacetate path did not interfere with the measurement of phenylalanine ammonia-lyase activity. Activity of cinnamic acid 4-hydroxylase (EC 1.14.13.11) showed an early peak after 8 hours illumination, declined thereafter sharply, then gradually increased during the remainder of the experiment. Activities of chalcone synthase and UDP glucose:flavonol 3-O-glucosyltransferase (EC 2.4.1.91) increased steadily and reached a plateau after approximately 70 hours illumination time. Activity of 4-hydroxycinnamate:coenzyme A ligase (EC 6.2.1.12) remained relatively unchanged, whereas that of chalcone isomerase (EC 5.5.1.6) declined steadily during the course of the experiment. The relative in vitro enzyme activities suggest that the rate-limiting step for the phenylpropanoid path is the cinnamic acid 4-hydroxylase, that of the flavonoid pathway is the chalcone synthase. Integration of enzyme activity curves, however, show that only the curve deriving from phenylanine ammonia-lyase activity matches closely the production of the flavonol glycosides.

Journal Article↗
PubMed1974

Interferon induction in rabbit cells irradiated with UV light.

UV irradiation of a continuous line of rabbit kidney cells (RK13) was used as a tool for the study of the mechanism of interferon induction. Irradiation of cells prior to their exposure to Newcastle disease virus (NDV) resulted in a dose-dependent decrease in interferon production. The inhibition of total cellular RNA synthesis by UV irradiation in uninduced cultures was similar to the inactivation curve of interferon production in NDV-induced cultures. In contrast, the production of interferon with polyinosinate-polycytidylate (poly[I].poly [C]) paradoxically was enhanced in cells irradiated with a wide range of doses of UV. However, in cells stimulated with poly(I).poly(C) and "superinduced" by the sequential addition of cycloheximide and actinomycin D, the rate of inactivation of interferon production by UV light was similar to that observed with NDV. These results are not inconsistent with the idea that both poly(I).poly(C) and NDV stimulate the same interferon gene(s), but indicate that the mechanism controlling its expression may be different for each inducer.

Cell Line↗
PubMed1994

Blue and red light reversibly control psbA expression in the cyanobacterium Synechococcus sp. strain PCC 7942.

The three psbA genes encoding the photosystem II D1 protein in Synechococcus sp. strain PCC 7942 respond differentially to an increase in intensity of white light through transcriptional induction of psbAII and psbAIII and accelerated degradation of psbAI and psbAIII messages. We report that the genes exhibit a novel photoreversible response involving blue and red light that is almost indistinguishable from the high-white light response. Transfer of cells from white to low-fluence blue light caused a decrease in the level of the psbAI message and increased levels of psbAII and psbAIII messages, whereas transfer to red or far-red light had little effect. Five min of blue light was sufficient to trigger psbAII and psbAIII induction; five min of subsequent red irradiation attenuated this response, whereas subsequent green or far-red light (or darkness) had no effect. Response to both high and blue light was insensitive to inhibitors of photosynthetic electron transport. We propose that Synechococcus modulates photosystem II biosynthesis in a variable light environment through a photoreception signal pathway, which is independent of photosystem II activity and which is distinct from red/green-reversible control of chromatically adapting cyanobacteria and the red/far-red-reversible phytochrome of plants.

Bacterial Proteins↗
PubMed1976

Wound-induced phenylalanine ammonia-lyase in potato tuber tissue. Development of enzyme activity and effects of antibiotics.

Phenylalanine ammonia-lyase [EC 4.3.1.5.] activity increased rapidly after a 3-hr lag period in potato tuber (Solanum tuberosum L. cv. May Queen) disks incubated in a suitable medium in the dark at 25 degrees. The activity reached a maxinum after incubation for about 40 hr. The effects of actinomycin D, 6-methylpurine, cycloheximide, chloramphenicol, and mitomycin C on the induction of phenylalanine ammonia-lyase were investigated during incubation of the disks. Actinomycin D, 6-methylpurine, and cycloheximide all inhibited the formation of phenylalanine ammonia-lyase, though cycloheximide was the most effective at low concentrations. Application of actinomycin D for the initial lag period (3 hr) caused strong inhibition; however, if it was supplied later it did not inhibit but actually increased phenylalanine ammonialyase formation. In contrast, cycloheximide was effective over most of the incubation period. Chloramphenicol and mitomycin C did not inhibit phenylalanine phenylalanine ammonialyase induction, but markedly stimulated it. Light was not an essential factor for phenylalanine ammonia-lyase induction in the wounded tissue.

Ammonia-Lyases↗
PubMed1984

Regulatory idiotopes. Induction of idiotype-recognizing helper T cells by free light and heavy chains.

Previously, we have demonstrated the induction of T helper cells that recognize idiotype by antigen (19), idiotype (20), and antiidiotype (12). The T cell population has been characterized and found to recognize both the T15 and M167 myeloma proteins, which share PC binding specificity but differ in idiotypic specificities. In the present work, we used isolated heavy and light chains of T15 and M167 to generate T helper cells, and examined the response to trinitrophenyl (TNP)-T15 and TNP-M167. We found that the heavy chains induced a dose-dependent response to TNP-T15 and TNP-M167, while the light chain priming was ineffective. When isolated chains of a monoclonal anti-T15 antibody (F6-3) were used to induce idiotype-recognizing T cells, only the F6-3 light chains generated T cell help for TNP-T15 and TNP-M167. Evidently, the idiotypic determinant that is recognized by the T cells is not dependent upon the conformation of combined heavy and light chains. These data show that the Th2 helper cells for the T15/M167 idiotopes are induced by free heavy chains of T15 and M167; the Th1 T cells that interact with the Th2 population, of T15 and M167; the Th1 T cells that interact with the Th2 population, however, can be triggered by free light chains of an antiidiotypic hybridoma antibody. These provocative findings suggest a new model for the T helper cell network.

Animals↗
PubMed1987

Induction of phr gene expression by irradiation of ultraviolet light in Escherichia coli.

To measure the degree of phr gene induction by DNA-damaging agents, the promoter region was fused to the coding region of the lacZ gene in plasmid pMC1403. The new plasmids were introduced into Escherichia coli cells having different repair capabilities. More efficient induction of phr gene expression was detected in a uvrA- strain as compared with the wild-type strain. In addition, obvious induction was detected in uvrA- cells treated by 4-nitroquinoline 1-oxide and mitomycin C. Nalidixic acid, an inhibitor of DNA gyrase, also induced phr gene expression. In contrast, little induced gene expression was noted in UV-irradiated lexA- and recA- strains. It is suggested from these results that induction of the phr gene is one of the SOS responses. Possible nucleotide sequences which could be considered to constitute an SOS box were found at the regulator region of the phr gene.

Bacterial Proteins↗
PubMed1998

Identification of UV/blue light-response elements in the Arabidopsis thaliana chalcone synthase promoter using a homologous protoplast transient expression system.

To identify DNA sequences of the Arabidopsis thaliana chalcone synthase gene (CHS) concerned with induction by UV-B and UV-A/blue light, AtCHS promoter constructions were assayed by transient expression in protoplasts prepared from two different lines of cultured A. thaliana cells. The protoplasts responded similarly to A. thaliana leaf tissue in light-dependent CHS transcript accumulation. The reporter enzyme beta-glucuronidase (GUS) was used to monitor light-responsive promoter activity. A 1972 bp promoter conferred UV-B and UV-A/blue light induction of GUS activity. Deletion to 164 bp resulted in reduced promoter strength but retention of responsiveness to UV-B and UV-A/blue light. Further deletion abolished transcriptional activity. The 164 bp promoter contains sequences closely resembling LRUPcCHS, (light-responsive unit of the Petroselinum crispum CHS promoter). This A. thaliana CHS promoter region, designated LRUAtCHS, was sufficient to confer UV-B and UV-A/blue light responsiveness to a heterologous core promoter. Mutation of sequences in LRUAtCHS corresponding to the ACGT element and the MYB recognition element of LRUPcCHS resulted in inactivation of the 164 bp and 335 bp promoter deletions. However, the mutant 668 bp promoter retained residual UV-B and UV-A/blue light-induced expression, indicating the presence of additional functional sequences upstream of -335. Mutation of a single G-box-like sequence around -442 had no effect on light responsiveness, indicating that it does not function in light regulation of this promoter. Since no difference in responsiveness to UV-B and UV-A/blue light was observed with any promoter variant, we conclude that the two phototransduction pathways regulate transcription factors which interact with common promoter elements. The results from-our analysis of a A. thaliana light-responsive promoter will facilitate the study of light-dependent gene regulation by genetic means in Arabidopsis thaliana.

Acyltransferases↗
PubMed2000

A new type of mutation in the plant photoreceptor phytochrome B causes loss of photoreversibility and an extremely enhanced light sensitivity.

Photoreversibility, reversion of the inductive effect of a brief red light pulse by a subsequent far-red light pulse, is a property of photoresponses regulated by the plant photoreceptor phytochrome B (phyB). We screened for mutants with impaired photoreversibility to gain better insight into the phyB-specific signalling cascade. The phenotype of the mutant described is caused by a single amino acid exchange in a phyB subdomain that is highly conserved in all phytochromes but whose functional significance was unknown. The mutated phyB showed a slower dark reversion but no major alterations in its spectral properties. In addition to its loss of photoreversibility, the mutant also exhibited a hypersensitivity towards continuous red-light irradiation and an altered phenotype of adult plants under short-day conditions.

Alleles↗