High prevalence of T cell type I protein kinase A deficiency in systemic lupus erythematosus

Mitochondria, Oxidative Stress, cAMP Signalling and Apoptosis: A Crossroads in Lymphocytes of Multiple Sclerosis, a Possible Role of Nutraceutics

Multiple sclerosis (MS) is a complex inflammatory and neurodegenerative chronic disease that involves the immune and central nervous systems (CNS). The pathogenesis involves the loss of blood–brain barrier integrity, resulting in the invasion of lymphocytes into the CNS with consequent tissue damage. The MS etiology is probably a combination of immunological, genetic, and environmental factors. It has been proposed that T lymphocytes have a main role in the onset and propagation of MS, leading to the inflammation of white matter and myelin sheath destruction. Cyclic AMP (cAMP), mitochondrial dysfunction, and oxidative stress exert a role in the alteration of T lymphocytes homeostasis and are involved in the apoptosis resistance of immune cells with the consequent development of autoimmune diseases. The defective apoptosis of autoreactive lymphocytes in patients with MS, allows these cells to perpetuate, within the CNS, a continuous cycle of inflammation. In this review, we discuss the involvement in MS of cAMP pathway, mitochondria, reactive oxygen species (ROS), apoptosis, and their interaction in the alteration of T lymphocytes homeostasis. In addition, we discuss a series of nutraceutical compounds that could influence these aspects.

T-cell specific defect in expression of the NTPDase CD39 as a biomarker for lupus

Regulatory T cells (T(regs)) are critical for maintenance of peripheral tolerance via suppression of T-cell responses, and absence of T(regs) results in autoimmunity. The role of aberrations in the T(reg) pool for the development of systemic lupus erythematosus (SLE, lupus) remains uncertain. T(reg)-mediated generation of adenosine, dependent on the ectonucleotidase CD39, is an important mechanism for suppression of T-cell responses. We tested whether decreases in numbers of T(regs), and specifically CD39-expressing T(regs), are associated with human lupus. We studied 15 SLE patients, six patients with rheumatoid arthritis (RA) and 24 healthy controls. T(reg) phenotypic markers, including CD39 expression, were studied by flow cytometry. Varying numbers of sorted T(regs) cells were co-cultured with responder T (T(resp)) cells, with proliferation assessed by (3)H-thymidine incorporation. The proportion of T(regs) as defined by Foxp3(+) CD25(+high) CD127(-/low) was similar in lupus and control populations. CD39-expressing T(regs) comprised 37±13% of the T(reg) population in healthy controls and 36±21% in lupus subjects using nonsteroidal immunosuppressants to control active disease, but was nearly absent in five of six lupus subjects with minimally active disease. In contrast to healthy controls and lupus subjects without the CD39 defect, in SLE subjects with the CD39 defect, adenosine-dependent T(reg)-mediated suppression was nearly absent. These results suggest that functional defects in T(regs), rather than reduced T(reg) numbers, are important for the loss of peripheral tolerance in lupus. Presentation of this defect may serve as a biomarker for untreated disease.

Comprehensive and reliable phosphorylation site mapping of individual phosphoproteins by combination of multiple stage mass spectrometric analysis with a target-decoy database search

Since the emergence of proteomics, much attention has been paid to the development of new technologies for phosphoproteomcis analysis. Compared with large scale phosphorylation analysis at the proteome level, comprehensive and reliable phosphorylation site mapping of individual phosphoprotein is equally important. Here, we present a modified target-decoy database search strategy for confident phosphorylation site analysis of individual phosphoproteins without manual interpretation of spectra. Instead of using all protein sequences in a proteome database of an organism for the construction of a target-decoy database for phosphoproteome analysis, the composite database constructed for phosphorylation site analysis of individual phosphoproteins only included the sequences of the individual target proteins and a decoy version of a small inhomogeneous protein database. It was found that the confidence of phosphopeptide identifications could be effectively controlled when the acquired MS2 and MS3 spectra were searched against the above composite database followed with data processing. Because of the small size of the composite database, the computation time for the database search is very short, which allows the adoption of low-specificity proteases for protein digestion to increase the coverage of phosphorylation site mapping. The sensitivity and comprehensive phosphorylation site mapping of this approach was demonstrated by using two standard phosphoprotein samples of alpha-casein and beta-casein, and this approach was further applied to analyze the phosphorylation of the cyclic AMP-dependent protein kinase (PKA), which resulted in the identification of 17 phosphorylation sites, including five novel sites on four PKA subunits.

MECHANISMS OF DEFICIENT TYPE I PROTEIN KINASE A ACTIVITY IN LUPUS T LYMPHOCYTES

Systemic lupus erythematosus (SLE) is an autoimmune disease in which the immune response to antigen results in exaggerated CD4(+) T helper and diminished CD8(+) T cytotoxic responses. To determine the mechanisms underlying impaired T cell effector functions, we have investigated the cAMP/protein kinase A (cAMP/PKA) signaling pathway. The results demonstrate that diminished PKA-catalyzed protein phosphorylation is the result of deficient type I (PKA-I) and type II (PKA-II) isozyme-specific activities. The prevalence of deficient PKA-I and PKA-II activities in SLE T cells is approximately 80% and 40%, respectively. Diminished PKA-I activities are not associated with disease activity and appear to be stable over time. Two disparate mechanisms account for these low PKA-I and PKA-II isozyme activities. Moreover, novel transcript mutations of the RI alpha gene have been identified that are characterized by deletions, transitions, and transversions. Most mutations are clustered adjacent to GAGAG motifs and CT repeats. In conclusion, aberrant signaling via the cAMP/PKA pathway occurs in SLE T cells, and this is proposed to contribute to abnormal T cell effector functions.

Analysis of posttranslational modifications exemplified using protein kinase A

With the completion of the major genome projects, one focus in biomedical research has shifted from the analysis of the rather static genome to the highly dynamic proteome. The sequencing of whole genomes did not lead to much anticipated insights into disease mechanisms; however, it paved the way for proteomics by providing the databases for protein identification by peptide mass fingerprints. The relative protein distribution within a cell or tissue is subject to change upon external and internal stimuli. Signal transduction events extend beyond a simple change in protein levels; rather they are governed by posttranslational modifications (PTMs), which provide a quick and efficient way to modulate cellular signals. Because most PTMs change the mass of a protein, they are amenable to analysis by mass spectrometry. Their investigation adds a level of functionality to proteomics, which can be expected to greatly aid in the understanding of the complex cellular machinery involved in signal transduction, metabolism, differentiation or in disease. This review provides an overview on posttranslational modifications exemplified on the model system cAMP-dependent protein kinase. Strategies for detection of selected PTMs are described and discussed in the context of protein kinase function.

Abnormal intracellular distribution of NFAT1 in T lymphocytes from patients with systemic lupus erythematosus and characteristic clinical features

Systemic lupus erythematosus (SLE) presents various clinical features; however, underlying mechanisms remain unclear. In the immunity of SLE, impaired T cell receptor (TCR) signaling and altered cytokine production are in the center of pathogenesis, although, little is known about NFAT (nuclear factor of activated T cells) in lupus T lymphocytes. TCR stimulation activates NFAT1 through Ca2+/calcineurin (Cn) pathway, facilitating nuclear translocation of NFAT1 from cytosol. Therefore, we investigated relationship of disease activity/features and intracellular NFAT1 localization in T lymphocytes from active lupus patients by fractionation. Results showed no significant relationship between disease activity and NFAT1 distribution. However, interestingly, we observed skewed NFAT1 distribution in pellet in patients with active lupus nephritis or pleuritis. In vitro cyclosporin A treatment suggested autonomously activated Ca2+/Cn pathway in lupus T lymphocytes. Considering these results, NFAT1 might be presenting the clinical heterogeneity in SLE.

Quantification of cAMP antagonist action in vitro and in living cells

cAMP-dependent protein kinase (PKA) plays a key role in intracellular signalling. cAMP antagonists, acting as suppressors of PKA activity by preventing PKA-holoenzyme dissociation, have received increasing attention because of their potential use in diagnostics as well as for therapeutic purposes. A large number of cAMP analogs have been described over the last three decades and methodology has been established to monitor cAMP agonists action by either following enzymatic activity or holoenzyme dissociation. This is not the case for cAMP antagonists, where only a few substances have been demonstrated to exhibit effects in the low micromolar range, for example, Rp-8-Br-cAMPS. A main drawback in the development of new compounds is the lack of technologies to assess antagonist action in an in vitro situation as well as in living cells. Here we quantify the effect of several cAMP analogs applying three different biochemical/biophysical assay setups and one in-cell assay. This includes two methods monitoring subunit dissociation in a test tube, namely AlphaScreen, a bead-based proximity assay, and surface plasmon resonance, determining the association and dissociation patterns of the two PKA subunits in real time in response to antagonists. BRET(2), performed in living cells in a 96-well format, allows testing for the efficacy of membrane-permeable cAMP analogs based on a genetically engineered cAMP sensor. Using novel and established experimental strategies side by side, the action of cAMP and cAMP analogs was tested on type Ialpha PKA holoenzyme, thus generating methodology to screen drug libraries for potential cAMP antagonists with high accuracy, reproducibility as well as potential for automation.

Mitochondrial dysfunction in T cells of patients with systemic lupus erythematosus

Activation, proliferation, or programmed cell death of T lymphocytes are dependent on controlled reactive oxygen intermediates (ROI) production and ATP synthesis in mitochondria. The mitochondrial transmembrane potential (Delta Psi(m)) also plays a decisive role in cell survival by controlling activity of redox-sensitive caspases. T lymphocytes of patients with systemic lupus erythematosus (SLE) exhibit mitochondrial hyperpolarization, increased ROI production, diminished intracellular glutathione levels, cytoplasmic alkalinization, and ATP depletion that mediate enhanced spontaneous and diminished activation-induced apoptosis and sensitize lupus T cells to necrosis. These redox and metabolic checkpoints represent novel targets for pharmacological intervention in SLE.

Down-Regulation of IL-2 Production in T Lymphocytes by Phosphorylated Protein Kinase A-RIIβ

The beta isoform of the type II regulatory subunit (RIIbeta) of protein kinase A suppresses CREB transcriptional activity and c-Fos production in T cells following activation via the TCR. Because CREB is an integral nuclear transcription factor for IL-2 production by T cells, we tested the hypothesis that RIIbeta down-regulates IL-2 expression and IL-2 production in T cells. Stable transfection of RIIbeta in Jurkat T cells led to an approximately 90% reduction in IL-2 mRNA and IL-2 protein following T cell activation. The inhibition of IL-2 production was associated with phosphorylation of the RIIbeta subunit at serine 114 (pRIIbeta) and localization of pRIIbeta in intranuclear clusters. A serine 114 phosphorylation-defective mutant, RIIbeta(S114A), did not form these intranuclear clusters as well as wild-type RIIbeta, and did not inhibit IL-2 mRNA and protein synthesis, indicating that serine 114 phosphorylation is required for both nuclear localization and down-regulation of IL-2 production by RIIbeta. In contrast to its effect on IL-2, RIIbeta induced constitutive up-regulation of CD154 mRNA and cell surface expression. Thus, pRIIbeta differentially regulates gene expression following T cell activation. Unexpectedly, we also found that stable overexpression of another protein kinase A regulatory subunit, RIalpha, had the opposite effect on IL-2 expression, causing a 3- to 4-fold increase in IL-2 production following stimulation. In summary, our data demonstrate a novel mechanism by which serine 114 phosphorylation and nuclear localization of RIIbeta controls the regulation of gene expression in T cells.

Protein kinase A regulatory subunit type II beta directly interacts with and suppresses CREB transcriptional activity in activated T cells

Levels of the type IIbeta regulatory subunit (RIIbeta) of protein kinase A are abnormally high in the nuclei of T cells of some subjects with the autoimmune disorder systemic lupus erythematosus (SLE). However, the role of nuclear RIIbeta in the regulation of T cell function is unknown. Based on previous studies demonstrating that nuclear protein kinase A-RII subunits can modify cAMP response element (CRE)-dependent transcription, we tested the hypothesis that nuclear RIIbeta can alter CRE-directed gene expression in T cells through interaction with the nuclear transcription factor CRE-binding protein CREB. To test this hypothesis, we used the RIIbeta-deficient S49 and the Jurkat T cell lines. In both cell lines, transient transfection of RIIbeta resulted in nuclear localization of a portion of the ectopically expressed RIIbeta. In vitro and in vivo analyses revealed a novel, specific interaction between RIIbeta and CREB that mapped to the N-terminal 135 aa of RIIbeta. In functional studies, RIIbeta inhibited the transcriptional activity of a GAL4-CREB fusion protein by 67% in Jurkat T cells following activation with anti-CD3 and anti-CD28 mAbs. Importantly, deletion of the CREB-binding region of RIIbeta completely abrogated inhibition. Additionally, RIIbeta suppressed CRE-directed reporter gene expression and substantially reduced induction of promoter activity and endogenous protein levels of the CREB-dependent gene, c-fos, in activated T cells. We conclude that nuclear RIIbeta can act as a repressor of CREB transcriptional activity in T cells, providing a potential functional significance for aberrant levels of nuclear RIIbeta in systemic lupus erythematosus T cells.

Was it there all the time?

The complement system is old, yet it may still have something new to teach us. For many years, research has existed which shows that C3d, in addition to its established role as an adjuvant, could have an immunosuppressive activity. Being true, it suggests that a common mechanism may be used both by organisms and by their pathogens to prevent unwanted immune responses.

Immunopathology and the gene therapy of lupus

Lupus is a chronic autoimmune inflammatory disease with complex clinical manifestations. In humans, lupus, also known as systemic lupus erythematosus (SLE), affects between 40 and 250 individuals, mostly females, in each 100 000 of the population. There are also a number of murine models of lupus widely used in studies of the genetics, immunopathology, and treatment of lupus. Human patients and murine models of lupus manifest a wide range of immunological abnormalities. The most pervasive of these are: (1) the ability to produce pathogenic autoantibodies; (2) lack of T- and B-lymphocyte regulation; and (3) defective clearance of autoantigens and immune complexes. This article briefly reviews immunological abnormalities and disease mechanisms characteristic of lupus autoimmunity and highlight recent studies on the use of gene therapy to target these abnormalities.

Increased ubiquitination and reduced expression of LCK in T lymphocytes from patients with systemic lupus erythematosus

OBJECTIVE

To explore regulation of proximal signaling and composition of lipid rafts in T lymphocytes from patients with systemic lupus erythematosus (SLE).

METHODS

The expression, phosphorylation, and degradation of lipid raft-associated signaling molecules in T lymphocytes from 50 patients with SLE compared with 28 healthy controls and 22 rheumatoid arthritis patients were investigated. Lipid raft and nonraft fractions from T cells were isolated by ultracentrifugation. Proteins in the lipid raft and nonraft fractions were analyzed by Western blotting and probed for phosphotyrosine activity and for LCK, LAT, and CD3 epsilon. Immunoprecipitation experiments were performed to assess protein ubiquitination in T cell lysates. T cell phenotype and levels of intracellular LCK were determined by flow cytometry.

RESULTS

LCK, an essential signaling molecule for T cell activation, was significantly reduced in both lipid raft and nonraft fractions of T lymphocytes from patients with active SLE compared with controls, and the reduction was independent of treatment. To identify the likely causes of reduced LCK, we explored the possibility that chronic activation of T lymphocytes underlies LCK degradation. The results revealed an increase in protein ubiquitination, and specifically LCK ubiquitination, in T cells from SLE patients. However, our findings suggest that the increase in ubiquitination is independent of T cell activation.

CONCLUSION

LCK is reduced in T cell lipid rafts from patients with SLE. This reduction appears to be independent of activation and may be associated with abnormal ubiquitin-mediated regulation mechanisms.

Intrinsic T cell defects in systemic autoimmunity

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by loss of T cell tolerance to nuclear antigens. Studies in mice and humans have demonstrated that T cells from individuals with lupus are abnormal. Here, we review the known T cell defects in lupus and their possible biochemical nature, genetic causes, and significance for lupus pathogenesis.

CD4+ T cells from lupus-prone mice avoid antigen-specific tolerance induction in vivo

Activated T cells in spontaneous lupus presumably bypass normal tolerance mechanisms in the periphery, since thymic tolerance appears intact. To determine whether such T cells indeed avoid in vivo peripheral tolerance mechanisms, we assessed their activation and recall responses after in vivo Ag stimulation in the absence of exogenously supplied costimulatory signals. Naive CD4(+) AND (transgenic mice bearing rearranged TCR specific for pigeon cytochrome c, peptides 88-104) TCR-transgenic T cells, specific for pigeon cytochrome c, from lupus-prone Fas-intact MRL/Mp+(Fas-lpr) and from H-2(k)-matched control CBA/CaJ and B10.BR mice (MRL.AND, CBA.AND, and B10.AND, respectively) were adoptively transferred into (MRL x CBA)F(1) or (MRL x B10)F(1) recipients transgenically expressing membrane-bound pigeon cytochrome c as a self-Ag. MRL.AND and control CBA.AND and B10.AND-transgenic T cells were activated and divided after transfer, indicating encounter with their cognate Ag; however, T cells from CBA.AND and B10.AND mice were impaired in their ability to proliferate and produce IL-2 after challenge with pigeon cytochrome c in ex vivo recall assays, a typical phenotype of anergized cells. By contrast, MRL.AND T cells proliferated more, and a significantly higher percentage of such cells produced IL-2, compared with control T cells. This observation that MRL T cells avoided anergy induction in vivo was confirmed in an in vitro system where the cells were stimulated with an anti-CD3 in the absence of a costimulatory signal. These experiments provide direct evidence that CD4(+) T cells from Fas-intact lupus-prone MRL mice are more resistant than nonautoimmune control cells to anergy induction. Anergy avoidance in the periphery might contribute to the characteristic finding in lupus of inappropriate T cell activation in response to ubiquitous self-Ags.

Transcript mutations of the alpha regulatory subunit of protein kinase A and up-regulation of the RNA-editing gene transcript in lupus T lymphocytes

BACKGROUND

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterised by diverse dysfunctions of immune effector cells, including proliferation and cytotoxicity. In T cells from patients with SLE, activity of type 1 protein kinase A isozymes is greatly reduced because of decreased expression of the alpha and beta regulatory subunits (RI alpha and RI beta). We aimed to identify a molecular mechanism or mechanisms for this isozyme deficiency by assessing occurrence of mutations in transcripts of the RI alpha subunit in patients with SLE.

METHODS

We cloned and sequenced cDNA of RI alpha and corresponding genomic DNA of the coding region to detect sequence changes from eight patients with SLE and six healthy controls. Because transcript editing is regulated by adenosine deaminases that act on RNA (ADAR), we quantified expression of ADAR1 transcripts in SLE and control T cells by competitive PCR.

FINDINGS

Sequence analyses of cDNA showed heterogeneous transcript mutations, including deletions, transitions, and transversions. We identified 1.22 x 10(-3)/bp transcript mutations in SLE T cells-a frequency 7.5 times higher than that in control T cells. By contrast, we identified no genomic mutations. Two hotspots were identified in the RI alpha subunit transcripts from SLE T cells, one located adjacent to a pseudosubstrate site of the RI alpha subunit and the other a component of the cAMP binding A domain. ADAR1 mRNA content was 3.5 times higher in SLE cells than in control T cells (p=0.001).

INTERPRETATION

An RNA-editing enzyme could be converting adenosine to inosine within double-stranded regions of RNA, resulting in transcript mutations. This process could be one mechanism resulting in mutations in the RI alpha subunit of type 1 protein kinase A.

Persistent mitochondrial hyperpolarization, increased reactive oxygen intermediate production, and cytoplasmic alkalinization characterize altered IL-10 signaling in patients with systemic lupus erythematosus

Abnormal death signaling in lymphocytes of systemic lupus erythematosus (SLE) patients has been associated with elevation of the mitochondrial transmembrane potential (Delta psi(m)) and increased production of reactive oxygen intermediates (ROI). The resultant ATP depletion sensitizes T cells for necrosis that may significantly contribute to inflammation in patients with SLE. In the present study, the role of mitochondrial signal processing in T cell activation was investigated. CD3/CD28 costimulation of PBL elicited transient mitochondrial hyperpolarization and intracellular pH (pH(i)) elevation, followed by increased ROI production. Baseline Delta psi(m), ROI production, and pH(i) were elevated, while T cell activation-induced changes were blunted in 15 patients with SLE in comparison with 10 healthy donors and 10 rheumatoid arthritis patients. Similar to CD3/CD28 costimulation, treatment of control PBL with IL-3, IL-10, TGF-beta(1), and IFN-gamma led to transient Delta psi(m) elevation. IL-10 had diametrically opposing effects on mitochondrial signaling in lupus and control donors. Unlike healthy or rheumatoid arthritis PBL, cells of lupus patients were resistant to IL-10-induced mitochondrial hyperpolarization. By contrast, IL-10 enhanced ROI production and cell death in lupus PBL without affecting ROI levels and survival of control PBL. Ab-mediated IL-10 blockade or stimulation with antagonistic lymphokine IL-12 normalized baseline and CD3/CD28-induced changes in ROI production and pH(i) with no impact on Delta psi(m) of lupus PBL. The results suggest that mitochondrial hyperpolarization, increased ROI production, and cytoplasmic alkalinization play crucial roles in altered IL-10 responsiveness in SLE.

Deficient protein kinase a in systemic lupus erythematosus: a disorder of T lymphocyte signal transduction

Systemic lupus erythematosus (SLE) is an idiopathic autoimmune disease characterized by impaired T lymphocyte immune effector functions. We have identified a disorder of signal transduction in SLE T cells involving the cyclic AMP/protein kinase A (cAMP/PKA) pathway. Cyclic AMP-stimulated PKA-catalyzed protein phosphorylation is markedly diminished owing to profound deficiencies of both type I (PKA-I) and type II (PKA-II) isozyme activities. Deficient PKA-I isozyme is characterized by a significant reduction in the amount of type I regulatory beta subunit (RI beta) steady state mRNA by competitive polymerase chain reaction. This is associated with a 30% decrease in RI alpha protein and a 65% reduction in RI beta protein. Indeed, T cells from approximately 25% of SLE subjects have no detectable RI beta protein. Transient transfection of T cells not expressing RI beta protein with autologous SLE RI beta cDNA bypassed the block in translation, reconstituting PKA activity and augmenting IL-2 production. Of importance was the initial identification of novel RI alpha mRNA mutations characterized by heterogeneous transcript mutations, including deletions, transitions, and transversions. Most mutations are clustered adjacent to GAGAG motifs and CT repeats. By contrast, deficient PKA-II activity is the result of spontaneous dissociation of the cytosolic RII beta(2)C(2) holoenzyme, aberrant RII beta translocation to the nucleus from the cytosol, and retention of RII beta in the nucleus. In conclusion, distinct mechanisms account for deficient PKA-I and PKA-II isozyme activities in SLE T cells.

Molecular mechanisms for protein kinase A-mediated modulation of immune function

Protein kinase A (PKA) is a serine/threonine kinase that regulates a number of cellular processes important for immune activation and control. Modulation of signal transduction by PKA is a complex and diverse process, and differential isozyme expression, holoenzyme composition and subcellular localization contribute specificity to the PKA signalling pathway. In lymphocytes, phosphorylation by PKA has been demonstrated to regulate antigen receptor-induced signalling both by altering protein-protein interactions and by changing the enzymatic activity of target proteins. PKA substrates involved in immune activation include transcription factors, members of the MAP kinase pathway and phospholipases. The ability of PKA type I to regulate activation of signalling components important for formation of the immunological synapse, demonstrates that the cAMP signalling pathway can directly modulate proximal events in lymphocyte activation. Furthermore, the recent discovery that PKA regulates Src kinases through modulation of Csk, supports the notion that PKA is involved in the fine-tuning of immune receptor signalling in lipid rafts.

Protein kinase A RI beta subunit deficiency in lupus T lymphocytes: bypassing a block in RI beta translation reconstitutes protein kinase A activity and augments IL-2 production

A profound deficiency of type I protein kinase A (PKA-I or RIalpha/beta2C2) phosphotransferase activity occurs in the T lymphocytes of 80% of subjects with systemic lupus erythematosus (SLE), an autoimmune disorder of unknown etiology. This isozyme deficiency is predominantly the product of reduced or absent beta isoform of the type I regulatory subunit (RIbeta). Transient transfection of RIbeta cDNAs from SLE subjects into autologous T cells that do not synthesize the RIbeta subunit bypassed the block, resulting in RIbeta subunit synthesis and restoration of the PKA-Ibeta (RIbeta2C2) holoenzyme. Transfected T cells activated via the T cell surface receptor complex revealed a significant increase of cAMP-activatable PKA activity that was associated with a significant increase in IL-2 production. These data demonstrate that a disorder of RIbeta translation exists, and that correction of the PKA-I deficiency may enhance T lymphocyte effector functions in SLE.

Gender differences in autoimmunity: molecular basis for estrogen effects in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that occurs primarily in women (9:1 compared to men). Estrogen is a female sex hormone that acts on target cells through specific receptor proteins and alters the rate of transcription of target genes. Experiments in our laboratory have shown that calcineurin steady-state mRNA levels and phosphatase activity increase when estrogen is cultured with SLE T cells. This estrogen-dependent increase is dose-dependent, hormone-specific and temporally regulated. Estrogen receptor antagonism by ICI 182,780 inhibits the increase in calcineurin mRNA and phosphatase activity, while cycloheximide has no effect suggesting that new protein synthesis is not required. Reverse transcription and polymerase chain amplification indicate that estrogen receptor-alpha and estrogen-beta are expressed in human T cells. However, calcineurin does not respond to estrogen stimulation in T cells from normal females, males and lupus males. Taken together, these results indicate a differential function of the estrogen receptor in women with lupus. A model is proposed that suggests estrogen, acting through the estrogen receptor, enhances T cell activation in women with lupus resulting in amplified T-B cells interactions, B cell activation and autoantibody production.

Glucocorticosteroid dependent decrease in the activity of calcineurin in the peripheral blood mononuclear cells of patients with systemic lupus erythematosus

OBJECTIVE

To compare the activity of calcineurin in the peripheral blood mononuclear cells (PBMC) of 32 patients with systemic lupus erythematosus (SLE) and 35 healthy controls.

METHODS

The activity of calcineurin was assayed in the supernatants of sonicated mononuclear cells.

RESULTS

There was no significant difference in the calcineurin activity of patients with SLE not taking glucocorticosteroids (GCS) compared with the healthy controls. On the other hand, the activity of calcineurin was reduced in patients with SLE taking GCS, correlating negatively with the dose of GCS. The stimulation of PBMC by phorbol ester and calcium ionophore decreased the calcineurin activity both in patients with SLE and in healthy controls. GCS could also reduce calcineurin activity in the mononuclear cells of healthy subjects in vitro.

CONCLUSIONS

In patients with SLE the decrease in the calcineurin activity of PBMC depended on the dose of GCS used for treatment, and it was not a disease specific alteration. The higher the dose of GCS, the greater the inhibition of calcineurin activity. The reduction of calcineurin activity is a new element in the immunosuppressive effects of GCS during the treatment of patients with SLE.

Regulatory defects in Cbl and mitogen-activated protein kinase (extracellular signal-related kinase) pathways cause persistent hyperexpression of CD40 ligand in human lupus T cells

To identify intrinsic defects in lupus, we studied short-term, CD4(+) T cell lines that were established from 16 lupus patients (active or inactive) and 15 normal subjects by stimulating once with anti-CD3, anti-CD28, and IL-2. After resting, the pure CD4(+) T cells were exposed to anergy-inducing stimulation with plate-bound anti-CD3 mAb in the absence of APC. Lupus T cells showed prolonged high level expression of CD40 ligand (CD40L, CD154) even in the face of anergy protocol, which shut down CD40L expression in normal T cells. The sustained CD40L expression in lupus T cells did not correlate with memory status or Th deviation, and was relatively independent of IL-2 or other autocrine or paracrine signals via CD28 or CTLA-4. Cyclosporin A could block CD40L expression by lupus T cells when added early during the anti-CD3 stimulation period, but only partially when added later, indicating that another mechanism regulates the prolonged hyperexpression of CD40L besides the Ca(2+) --> calcineurin-dependent NF-AT pathway. When exposed to the anergy protocol, lupus T cells, in marked contrast to normal T cells, did not phosphorylate Cbl/Cbl-b but continued to express strongly phosphorylated extracellular signal-regulated kinase (ERK); U0126, a specific inhibitor of mitogen-activated protein kinase kinase --> ERK, could block both the early and the prolonged hyperexpression of CD40L. Thus, pathways regulating the activities of Cbl and one particular mitogen-activated protein kinase, ERK, are involved in the prolonged hyperexpression of CD40L in lupus T cells.

mRNA mutations of type I protein kinase A regulatory subunit alpha in T lymphocytes of a subject with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disorder of indeterminate etiology characterized by multiple T lymphocyte immune effector dysfunctions. Protein kinase A (PKA) isozymes contribute to the regulation of T cell immune effector functions. In SLE T cells, there is a profound deficiency of PKA-I isozyme activity characterized by both reduced RI alpha transcript and RI alpha protein levels. To identify a molecular mechanism(s) for this isozyme deficiency, we utilized single-strand conformation polymorphism (SSCP) analysis to detect structural changes in the cDNA. Of 10 SLE subjects, cDNAs from a single subject revealed a shifted band. Sequence analyses demonstrated that a shifted SSCP band from SLE T cells carried heterogeneous transcript mutations, including deletions, transitions and transversions. Most of these transcript mutations are clustered adjacent to GAGAG motifs and CT repeats-regions that are susceptible to transcript editing and/or molecular misreading. By contrast, no genomic mutations were identified. These results suggest the occurrence of mRNA editing and/or defective function of RNA polymerase in a subject with SLE. Mutant RI alpha transcripts are pathophysiolgically significant, for they can encode diverse, aberrant RI alpha isoforms, including truncated, dominant-negative subunits, resulting in deficient PKA-I activity. We propose that deficient PKA-I isozyme activity contributes to the pathogenesis of SLE by hindering effective signal transduction and impairing T cell effector functions.

Association of deficient type II protein kinase A activity with aberrant nuclear translocation of the RII beta subunit in systemic lupus erythematosus T lymphocytes

Systemic lupus erythematosus (SLE) is an autoimmune disorder of indeterminate etiology characterized by abnormal T cell signal transduction and altered T cell effector functions. We have previously observed a profound deficiency of total protein kinase A (PKA) phosphotransferase activity in SLE T cells. Here we examined whether reduced total PKA activity in SLE T cells is in part the result of deficient type II PKA (PKA-II) isozyme activity. The mean PKA-II activity in SLE T cells was 61% of normal control T cells. The prevalence of deficient PKA-II activity in 35 SLE subjects was 37%. Deficient isozyme activity was persistent over time and was unrelated to SLE disease activity. Reduced PKA-II activity was associated with spontaneous dissociation of the cytosolic RIIbeta2C2 holoenzyme and translocation of the regulatory (RIIbeta) subunit from the cytosol to the nucleus. Confocal immunofluorescence microscopy revealed that the RIIbeta subunit was present in approximately 60% of SLE T cell nuclei compared with only 2-3% of normal and disease controls. Quantification of nuclear RIIbeta subunit protein content by immunoprecipitation and immunoblotting demonstrated a 54% increase over normal T cell nuclei. Moreover, the RIIbeta subunit was retained in SLE T cell nuclei, failed to relocate to the cytosol, and was associated with a persistent deficiency of PKA-II activity. In conclusion, we describe a novel mechanism of deficient PKA-II isozyme activity due to aberrant nuclear translocation of the RIIbeta subunit and its retention in the nucleus in SLE T cells. Deficient PKA-II activity may contribute to impaired signaling in SLE T cells.

Molecular mechanisms involved in the estrogen-dependent regulation of calcineurin in systemic lupus erythematosus T cells

Previous experiments in our laboratory indicated that calcineurin expression and PP2B phosphatase activity increased when estrogen was cultured with SLE T cells but not with T cells from normal women. In this report we extended our findings to show that estrogen receptor (ER) antagonism by ICI 182,780 inhibited the estrogen-dependent increase in calcineurin mRNA and phosphatase PP2B activity indicating that estrogen action was mediated through the ER. Inhibition of de novo protein synthesis with cycloheximide suggested that the estrogen-dependent increase in T cell calcineurin mRNA was a direct effect of the ER and new protein synthesis was not required. Estrogen increased calcineurin mRNA in systemic lupus erythematosus (SLE) T cells at 6 h after the start of culture correlating with increased phosphatase activity at this same time. Phosphatase activity increased significantly (P < 0.02) in lupus T cells cultured for 8 h in estradiol-containing medium. Reverse transcription and polymerase chain amplification revealed that ER-beta and ER-alpha were expressed in female and male T cells from SLE patients and normal controls. However, calcineurin steady-state mRNA levels were unaffected by estradiol in cultured T cells from male SLE patients and normal male and female controls. These data indicate that estrogen, bound to the ER, evokes a direct increase in calcineurin expression in T cells from female lupus patients. This gender-specific response suggests that ER function is altered in women with the female predominant autoimmune disease, SLE.

Diminished Levels of Protein Kinase A RIα and RIβ Transcripts and Proteins in Systemic Lupus Erythematosus T Lymphocytes

Deficient type I protein kinase A phosphotransferase activity occurs in the T cells of 80% of subjects with systemic lupus erythematosus (SLE). To investigate the mechanism of this deficient isozyme activity, we hypothesized that reduced amounts of type I regulatory (RI) isoform transcripts, RIα and RIβ, may be associated with a diminution of RIα and/or RIβ protein. Sixteen SLE subjects with a mean (±1 SD) SLE disease activity index of 12.4 ± 7.2 were studied. Controls included 16 normal subjects, six subjects with primary Sjögren’s syndrome (SS), and three subjects with SS/SLE overlap. RT-PCR revealed that normal, SS, SS/SLE, and SLE T cells expressed mRNAs for all seven R and catalytic (C) subunit isoforms. Quantification of mRNAs by competitive PCR revealed that the ratio of RIα mRNA to RIβ mRNA in normal T cells was 3.4:1. In SLE T cells there were 20 and 49% decreases in RIα and RIβ mRNAs (RIβ; p = 0.008), respectively, resulting in an RIα:RIβ mRNA of 5.3:1. SS/SLE T cells showed a 72.5% decrease in RIβ mRNA compared with normal controls (p = 0.01). Immunoblotting of normal T cell RIα and RIβ proteins revealed a ratio of RIα:RIβ of 3.2:1. In SLE T cells, there was a 30% decrease in RIα protein (p = 0.002) and a 65% decrease in RIβ protein (p &lt; 0.001), shifting the ratio of RIα:RIβ protein to 6.5:1. T cells from 25% of SLE subjects lacked any detectable RIβ protein. Analysis of several lupus T cell lines demonstrated a persistent deficiency of both proteins, excluding a potential effect of disease activity. In conclusion, reduced expression of RIα and RIβ transcripts is associated with a decrement in RIα and RIβ proteins and may contribute to deficient type I protein kinase A isozyme activity in SLE T cells.