KU 70/80 lupus autoantigen is the transcription factor induced by interleukins (IL)-13 and -4 leading to induction of 15-lipoxygenase (15-LO) in human cells

Epigenetic and transcriptional control of the 15-lipoxygenase-1 gene in a Hodgkin lymphoma cell line

Lipoxygenases oxidatively metabolize polyunsaturated fatty acids to a rich spectrum of biologically active metabolites. The present study aimed at delineating the transcriptional and epigenetic mechanisms leading to 15-lipoxygenase-1 (15-LOX-1) expression in the Hodgkin lymphoma (HL) cell line L1236. Examination of the 15-LOX-1 5' promoter region demonstrated three putative binding sites for signal transducer and activator of transcription (STAT6) within the proximal 1200 base pairs relative to the start codon. Analysis by serial promoter deletions and STAT6 binding site mutations indicated that all three STAT6 binding sites are required for full activation of the 15-LOX-1 promoter. Chromatin immunoprecipitation assay demonstrated that these regions were occupied by STAT6 in L1236 (15-LOX-1 positive) but not in L428 (15-LOX-1 negative) cultured HL cells. Furthermore, DNA hypomethylation and histone hyperacetylation were detectable within the core promoter region of 15-LOX-1 only in L1236 cells but not L428 cells. Taken together, our data indicate that STAT6 activation and chromatin remodeling by DNA demethylation and histone acetylation are crucial for transcriptional activation of 15-LOX-1 in cultured HL cells. These prerequisites are fulfilled in the L1236 cell line, but not in the L428 cell line.

Age-related decrease in 15-lipoxygenase contributes to reduced vasorelaxation in rabbit aorta

Rabbit 15-lipoxygenase-1 (15-LO-1) oxygenates arachidonic acid (AA) into 15-hydroperoxyeicosatetraenoic acid, which is then converted to the vasodilatory 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and 11,12,15-trihydroxyeicosatrienoic acid (THETA). We studied the age-dependent expression of the 15-LO-1 in rabbit aorta and its effects on the synthesis of THETA, HEETA, and vasoactivity. Aortas of 1-wk-old rabbits express greater amounts of 15-LO-1 mRNA and protein compared with aortas of 4-, 8-, or 16-wk-old rabbits. The synthesis of THETA and HEETA in the rabbit aorta was also reduced with age. THETA synthesis was maximal in 1-wk-old aortas but decreased in aortas of 4- (42%), 8- (4%), and 16-wk-old (1%) rabbits. Similarly, THETA and HEETA synthesis decreased with age in mesenteric arteries from 1-, 4-, 8-, and 16-wk-old rabbits. The maximum vasorelaxation response to acetylcholine (10−6M) in the presence of indomethacin and nitro-l-arginine decreased in the order of 1 wk (64.5 ± 6.9%), 4 wk (52.6 ± 8.9%), 8 wk (53.0 ± 9.4%), and 16 wk (33.3 ± 6.6%). Similarly, the maximum relaxation to AA (3 × 10−4M) decreased with age in the order of 1 wk (60.4 ± 8.9%), 4 wk (56.3 ± 5.8%), 8 wk (41.8 ± 12.3%), and 16 wk (28.9 ± 1.6%). In contrast, the vasorelaxation to sodium nitroprusside was not significantly altered by age. These data indicate that aortic 15-LO-1 expression and activity are downregulated with aging in rabbits. This decrease is paralleled by the reduced synthesis of vasoactive THETA and HEETA and aortic relaxations to acetylcholine and AA.

Functions of the histone chaperone nucleolin in diseases

Alteration of nuclear morphology is often used by pathologist as diagnostic marker for malignancies like cancer. In particular, the staining of cells by the silver staining methods (AgNOR) has been proved to be an important tool for predicting the clinical outcome of some cancer diseases. Two major argyrophilic proteins responsible for the strong staining of cells in interphase are the nucleophosmin (B23) and the nucleolin (C23) nucleolar proteins. Interestingly these two proteins have been described as chromatin associated proteins with histone chaperone activities and also as proteins able to regulate chromatin transcription. Nucleolin seems to be over-expressed in highly proliferative cells and is involved in many aspect of gene expression: chromatin remodeling, DNA recombination and replication, RNA transcription by RNA polymerase I and II, rRNA processing, mRNA stabilisation, cytokinesis and apoptosis. Interestingly, nucleolin is also found on the cell surface in a wide range of cancer cells, a property which is being used as a marker for the diagnosis of cancer and for the development of anti-cancer drugs to inhibit proliferation of cancer cells. In addition to its implication in cancer, nucleolin has been described not only as a marker or as a protein being involved in many diseases like viral infections, autoimmune diseases, Alzheimer's disease pathology but also in drug resistance. In this review we will focus on the chromatin associated functions of nucleolin and discuss the functions of nucleolin or its use as diagnostic marker and as a target for therapy

Model of stimulation-responsive splicing and strategies in identification of immunogenic isoforms of tumor antigens and autoantigens

We recently proposed a novel model of stimulation-responsive splicing for the selection of autoantigens and self-tumor antigens. Our model theorizes that the significantly higher rates of alternative splicing of autoantigen and self-tumor antigen transcripts that occur in response to stimuli could induce extra-thymic expression of untolerized antigen epitopes for elicitation of autoimmune and anti-tumor responses. To facilitate the identification of immunogenic isoforms of antigens, we have developed strategies using improved SEREX in conjunction with database-mining and immunogenic isoform mapping. Identification of immunogenic isoforms of autoantigens and self-tumor antigens is very important for the development of novel therapeutics and diagnostic tools for autoimmune diseases and tumors, such as: (1) autoantigen isoform microarrays for disease diagnosis and prognosis; (2) autoantigen isoform-specific tolerizing vaccines and splicing-redirection therapies, as well as (3) immunogenic antigen isoform-specific immunotherapy for tumors.

Increased noncanonical splicing of autoantigen transcripts provides the structural basis for expression of untolerized epitopes

BACKGROUND

Alternative splicing is important for increasing the complexity of the human proteome from a limited genome. Previous studies have shown that for some autoantigens, there is differential immunogenicity among alternatively spliced isoforms.

OBJECTIVES

Herein, we tested the hypothesis that alternative splicing is a common feature for transcripts of autologous proteins that are autoantigens. The corollary hypothesis tested was that nonautoantigen transcripts have a lower frequency of alternative splicing.

METHODS

The extent of alternative splicing within 45 randomly selected self-proteins associated with autoimmune diseases was compared with 9554 randomly selected proteins in the human genome by using bioinformatics analyses. Isoform-specific regions that resulted from alternative splicing were studied for their potential to be epitopes for antibodies or T-cell receptors.

RESULTS

Alternative splicing occurred in 100% of the autoantigen transcripts. This was significantly higher than the approximately 42% rate of alternative splicing observed in the 9554 randomly selected human gene transcripts ( P < .001). Within the isoform-specific regions of the autoantigens, 92% and 88% encoded MHC class I and class II-restricted T-cell antigen epitopes, respectively, and 70% encoded antibody binding domains. Furthermore, 80% of the autoantigen transcripts underwent noncanonical alternative splicing, which is also significantly higher than the less than 1% rate in randomly selected gene transcripts ( P < .001).

CONCLUSION

These studies suggest that noncanonical alternative splicing may be an important mechanism for the generation of untolerized epitopes that may lead to autoimmunity. Furthermore, the product of a transcript that does not undergo alternative splicing is unlikely to be a target antigen in autoimmunity.