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.

Fc epsilon receptor type I gamma chain replaces the deficient T cell receptor zeta chain in T cells of patients with systemic lupus erythematosus

OBJECTIVE

T cells from the majority of patients with systemic lupus erythematosus (SLE) express significantly lower levels of T cell receptor zeta chain, a critical signaling molecule. However, TCR/CD3 triggering of SLE T cells shows increased phosphorylation of downstream signaling intermediates and increased [Ca2+]i response, suggesting the presence of alternative signaling mechanisms. We investigated whether Fcepsilon receptor type I gamma chain (FcepsilonRIgamma) could substitute for TCR zeta chain and contribute to T cell signaling in SLE.

METHODS

T cells were purified from the peripheral blood of 21 patients with SLE and 5 healthy volunteers. The expression of FcepsilonRIgamma was investigated using immunoblotting, reverse transcriptase-polymerase chain reaction, and flow cytometry methods. Involvement of the FcepsilonRIgamma in T cell signaling was studied by immunoprecipitation and/or immunoblotting after TCR/CD3 stimulation.

RESULTS

Western blotting and densitometric analysis showed that the expression of FcepsilonRIgamma in SLE T cells was 4.3-fold higher than in normal T cells (P < 0.001). Flow cytometric analyses of T lymphocyte subsets revealed that the proportions of FcepsilonRIgamma+,CD3+, FcepsilonRIgamma+,CD4+, and FcepsilonRIgamma+, CD8+ cells were significantly greater in SLE patients than in healthy controls (P < 0.001). Immunoprecipitation of SLE T cell lysates with an anti-FcepsilonRIgamma antibody showed that FcepsilonRIgamma associates with the tyrosine kinase Syk and the CD3epsilon chain, suggesting that FcepsilonRIgamma is functionally involved in TCR signaling.

CONCLUSION

These results demonstrate that the FcepsilonRIgamma chain is expressed at high levels in a large proportion of SLE T cells. The increased expression of FcepsilonRIgamma chain in SLE T cells may account in part for the aberrant antigen receptor-initiated signaling and contribute to the diverse cellular abnormalities found in this disease.

T cell signaling abnormalities in systemic lupus erythematosus are associated with increased mutations/polymorphisms and splice variants of T cell receptor zeta chain messenger RNA

OBJECTIVE

T cells from patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain protein and messenger RNA (mRNA) expression. This study was undertaken to explore the possibility that coding-region mutations/polymorphisms of the TCR zeta chain could account for its decreased expression and altered signaling in SLE T cells.

METHODS

TCR zeta chain mRNA from 48 SLE patients, 18 disease controls, and 21 healthy volunteers was reverse transcribed, amplified by polymerase chain reaction, and cloned, and complementary DNA (cDNA) was sequenced. DNA sequences from multiple clones were analyzed for silent single-nucleotide polymorphisms, mutations, and splice variations, to promote the identification of heterozygosity.

RESULTS

DNA sequence analysis revealed several widely distributed missense mutations and silent polymorphisms in the coding region of the TCR zeta chain, which were more frequent in SLE patients than in patients with other rheumatic diseases or healthy controls (P < 0.0001). Several of the missense mutations were located in the 3 immunoreceptor tyrosine activation motifs or the GTP binding domain, and this could lead to functional alterations in the TCR zeta chain. A splice variant of the TCR zeta chain with a codon CAG (glutamine) insertion between exons IV and V was found in half of the SLE and control samples. Two larger spliced isoforms of the TCR zeta chain, with an insertion of 145 bases and 93 bases between exons I and II, were found only in SLE T cells. We also identified various alternatively spliced forms of the TCR zeta chain resulting from the deletion of individual exons II, VI, or VII, or a combined deletion of exons V and VI; VI and VII; II, III, and IV; or V, VI, and VII in SLE T cells. The frequency of the deletion splice variants was significantly higher in SLE than in control samples (P = 0.004). These variations were observed in cDNA and may not reflect the status of the genomic DNA.

CONCLUSION

These findings demonstrate that heterogeneous mutations/polymorphisms and alternative splicing of TCR zeta chain cDNA are more frequent in SLE T cells than in T cells from non-SLE subjects and may underlie the molecular basis of known T cell signaling abnormalities in this disease.

Molecular basis of deficient IL-2 production in T cells from patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disease characterized by diverse cellular and biochemical aberrations, including decreased production of IL-2. Here we show that nuclear extracts from unstimulated SLE T cells, unlike extracts from normal T cells, express increased amounts of phosphorylated cAMP-responsive element modulator (p-CREM) that binds the -180 site of the IL-2 promoter. Nuclear extracts from stimulated normal T cells display increased binding of phosphorylated cAMP-responsive element binding protein (p-CREB) to the -180 site of the IL-2 promoter, whereas nuclear extracts from stimulated SLE T cells display primarily p-CREM and decreased p-CREB binding. In SLE T cells, p-CREM bound to the transcriptional coactivators, CREB binding protein and p300. Increased expression of p-CREM correlated with decreased production of IL-2. The transcription of a reporter gene driven by the -180 site was enhanced in normal T cells, but was suppressed in SLE T cells. These experiments demonstrate that transcriptional repression is responsible for the decreased production of IL-2 by SLE T cells.

Polymorphisms/mutations of TCR-zeta-chain promoter and 3' untranslated region and selective expression of TCR zeta-chain with an alternatively spliced 3' untranslated region in patients with systemic lupus erythematosus

A vast majority of systemic lupus erythematosus (SLE) patients display decreased expression of TCR zeta-chain mRNA, a critical signaling molecule implicated in the selection of the TCR repertoire and in the prevention of autoimmunity. To identify the molecular mechanisms involved in the downregulation of TCR zeta-chain transcripts in SLE T cells, we investigated the possibility of polymorphisms/mutations in the promoter and the 3' untranslated region. PCR, cloning and sequence analysis of the promoter region from the genomic DNA showed significantly higher number of polymorphisms in SLE T cells compared to non-SLE control subjects (P = 0.044). Promoter sequence was also analysed from granulocytes to delineate the possibility of somatic mutations in activated SLE T cells. Promoter polymorphisms were significantly higher in granulocytes of SLE patients compared to non-SLE controls (P = 0.048), suggesting that these polymorphisms were of genomic origin. Nucleotide analysis of the promoter sequence revealed a -76T insertion compared to the published sequence, in all of the SLE samples and controls. RT-PCR analysis of the TCR zeta-chain 3' untranslated region showed a 344 bp product in addition to the expected 906 bp product. Cloning and sequence analysis of the 344 bp product indicated that it is an alternatively spliced form with both splicing donor and acceptor sites, resulting in deletion of nucleotides 672-1233 of TCR zeta-chain mRNA. Unlike the nomal TCR zeta-chain, the expression of TCR zeta-chain with the alternatively spliced 344 bp 3' untranslated region was higher in SLE T cells compared to non-SLE controls. The number of mutations/polymorphisms in the 906 bp TCR zeta-chain 3' untranslated region were significantly higher in SLE T cells compared to non-SLE subjects (P = 0.032). Frequent mutations/polymorphisms and aberrant splicing of the downstream 3' untranslated region may affect the stability and/or transport of TCR zeta-chain mRNA, leading to its downregulation in SLE T cells.

Trichostatin A reverses skewed expression of CD154, interleukin-10, and interferon-gamma gene and protein expression in lupus T cells

In systemic lupus erythematosus (SLE), T helper cells exhibit increased and prolonged expression of cell-surface CD40 ligand (CD154), spontaneously overproduce interleukin-10 (IL-10), but underproduce interferon-gamma (IFN-gamma). We tested the hypothesis that the imbalance of these gene products reflects skewed expression of CD154, IL-10, and IFN-gamma genes. Here, we demonstrate that the histone deacetylase inhibitor, trichostatin A, significantly down-regulated CD154 and IL-10 and up-regulated IFN-gamma gene expression in SLE T cells. This reversal corrected the aberrant expression of these gene products, thereby enhancing IFN-gamma production and inhibiting IL-10 and CD154 expression. That trichostatin A can simultaneously reverse the skewed expression of multiple genes implicated in the immunopathogenesis of SLE suggests that this pharmacologic agent may be a candidate for the treatment of this autoimmune disease.

Molecular aberrations in human systemic lupus erythematosus

Systemic lupus erythematosus is an autoimmune disorder that predominantly affects women during the childbearing years. Clinically, major organ systems are affected, including the skin, kidneys and nervous system. Genetic, hormonal, environmental and immunoregulatory factors contribute to the highly variable expression of the disease. Impaired cellular and humoral immune responses reflect disordered biochemical and molecular functions that might be determined genetically. Enhanced understanding of these molecular abnormalities should enable development of new, effective therapeutic agents in the near future.

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.

Systemic lupus erythematosus in the elderly

Aging modifies the clinical presentation and course of autoimmune disorders, although the mechanisms by which this occurs remain to be determined. Current evidence cited above supports the general concept that there is a natural senescence of the immune system. This evidence would suggest that somehow senescence directly affects gene expression, resulting in biochemical abnormalities that culminate in T-cell immunodysfunctions. This may be a principal factor that attenuates the autoimmune response to self-antigen and, therefore, the disease course. The authors speculate that there is a disorder primary to the T cell in SLE that is expressed as abnormal immunologic responses to self-antigens, resulting in autoimmunity. Although understanding of this primary T cell disorder is still limited, clinicians now know that the T cell harbors abnormal signaling pathways that reflect defective biochemical functions and seem to be genetically regulated. This aberrant signaling would be anticipated to affect both principal T cell subsets. It may hinder the capacity of cells, such as CD8 T cells, to effectively down-regulate the response of autoreactive CD4 helper T cells to autoantigens. Loss of self-regulation would manifest itself as loss of tolerance, a fundamental component of autoimmunity. The future challenge is to understand how aberrant signaling leads to loss of tolerance. Given this underlying genetic susceptibility in an aged individual whose T cells also are undergoing natural senescence, the authors suggest that it is conceivable that a stress factor may tip the balance in the favor of clinical disease. One such factor may be unspecified environmental stimuli. Yet another consideration is an intercurrent illness, such as an infection. It remains to be determined, however, what these environmental stimuli are and how they impact on the immune system to trigger disease.

Abnormal NF-kappa B activity in T lymphocytes from patients with systemic lupus erythematosus is associated with decreased p65-RelA protein expression

Numerous cellular and biochemical abnormalities in immune regulation have been described in patients with systemic lupus erythematosus (SLE), including surface Ag receptor-initiated signaling events and lymphokine production. Because NF-kappa B contributes to the transcription of numerous inflammatory genes and has been shown to be a molecular target of antiinflammatory drugs, we sought to characterize the functional role of the NF-kappa B protein complex in lupus T cells. Freshly isolated T cells from lupus patients, rheumatoid arthritis (RA) patients, and normal individuals were activated physiologically via the TCR with anti-CD3 and anti-CD28 Abs to assess proximal membrane signaling, and with PMA and a calcium ionophore (A23187) to bypass membrane-mediated signaling events. We measured the NF-kappa B binding activity in nuclear extracts by gel shift analysis. When compared with normal cells, the activation of NF-kappa B activity in SLE patients was significantly decreased in SLE, but not in RA, patients. NF-kappa B binding activity was absent in several SLE patients who were not receiving any medication, including corticosteroids. Also, NF-kappa B activity remained absent in follow-up studies. In supershift experiments using specific Abs, we showed that, in the group of SLE patients who displayed undetectable NF-kappa B activity, p65 complexes were not formed. Finally, immunoblot analysis of nuclear extracts showed decreased or absent p65 protein levels. As p65 complexes are transcriptionally active in comparison to the p50 homodimer, this novel finding may provide insight on the origin of abnormal cytokine or other gene transcription in SLE patients.

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

OBJECTIVE

To estimate the prevalence of protein kinase A type I isozyme (PKA-I) deficiency in a cohort of systemic lupus erythematosus (SLE) patients, and to establish whether the isozyme deficiency is associated with SLE disease activity.

METHODS

Thirty-five SLE patients and 35 age-, sex-, and race-matched normal controls were studied. Fifteen subjects were restudied on at least 3 occasions over a 4-year interval. Clinical disease activity was estimated by the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), and the T cell activation markers CD25+ and HLA-DR+ were quantified by flow cytometry. PKA-I isozyme activities were quantified in enriched T cells. Statistical analyses were performed by Student's t-test, Mann Whitney U test, and Pearson product moment test.

RESULTS

The mean PKA-I activity in SLE T cells (540 pmoles/minute/mg of protein) was significantly lower than that in control T cells (1,578 pmoles/ minute/mg of protein) (P<0.001). The prevalence of isozyme deficiency in this cohort was 80%. During a 4-year interval, PKA-I activities remained significantly reduced, whereas SLEDAI scores significantly improved. There was no relationship between deficient PKA-I activity and either SLEDAI scores or the proportion of T cells bearing CD25+ or HLA-DR+ activation markers.

CONCLUSION

There is a high prevalence of deficient T cell PKA-I isozyme activity in SLE that persists over time and is independent of SLE disease activity.

Diminished levels of protein kinase A RI alpha and RI beta 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, RIalpha and RIbeta, may be associated with a diminution of RIalpha and/or RIbeta 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 RIalpha mRNA to RIbeta mRNA in normal T cells was 3.4:1. In SLE T cells there were 20 and 49% decreases in RIalpha and RIbeta mRNAs (RIbeta; p = 0.008), respectively, resulting in an RIalpha:RIbeta mRNA of 5.3:1. SS/SLE T cells showed a 72.5% decrease in RIbeta mRNA compared with normal controls (p = 0.01). Immunoblotting of normal T cell RIalpha and RIbeta proteins revealed a ratio of RIalpha:RIbeta of 3.2:1. In SLE T cells, there was a 30% decrease in RIalpha protein (p = 0.002) and a 65% decrease in RIbeta protein (p < 0.001), shifting the ratio of RIalpha:RIbeta protein to 6.5:1. T cells from 25% of SLE subjects lacked any detectable RIbeta 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 RIalpha and RIbeta transcripts is associated with a decrement in RIalpha and RIbeta proteins and may contribute to deficient type I protein kinase A isozyme activity in SLE T cells.

Protein kinase A-catalyzed phosphorylation of heat shock protein 60 chaperone regulates its attachment to histone 2B in the T lymphocyte plasma membrane

Accumulating evidence suggests that the mitochondrial molecular chaperone heat shock protein 60 (hsp60) also can localize in extramitochondrial sites. However, direct evidence that hsp60 functions as a chaperone outside of mitochondria is presently lacking. A 60-kDa protein that is present in the plasma membrane of a human leukemic CD4(+) CEM-SS T cell line and is phosphorylated by protein kinase A (PKA) was identified as hsp60. An 18-kDa plasma membrane-associated protein coimmunoprecipitated with hsp60 and was identified as histone 2B (H2B). Hsp60 physically associated with H2B when both molecules were in their dephospho forms. By contrast, PKA-catalyzed phosphorylation of both hsp60 and H2B caused dissociation of H2B from hsp60 and loss of H2B from the plasma membrane of intact T cells. These results suggest that (i) hsp60 and H2B can localize in the T cell plasma membrane; (ii) hsp60 functions as a molecular chaperone for H2B; and (iii) PKA-catalyzed phosphorylation of both hsp60 and H2B appears to regulate the attachment of H2B to hsp60. We propose a model in which phosphorylation/dephosphorylation regulates chaperoning of H2B by hsp60 in the plasma membrane.

Clinical expression of autoimmune diseases in older adults

Aging modifies the clinical presentation and course of autoimmune disorders. In the older person who carries a complement of predisposing genes, environmental factors may alter a senescent immune system and trigger the onset of autoimmunity. In this article about autoimmune diseases of the older adult, the authors discuss the epidemiology, clinical presentations, laboratory and radiographic findings, and management of systemic lupus erythematosus, primary Sjogren's syndrome, and idiopathic inflammatory myopathies.

Familial clustering of end-stage renal disease in blacks with lupus nephritis

The factors that determine a patient's susceptibility to specific target organ involvement in systemic lupus erythematosus (SLE) remain unknown. Lupus nephritis can be a particularly devastating complication, with an increased mortality and the risk of progressive renal damage resulting in end-stage renal disease (ESRD). This analysis was performed to determine whether renal disease aggregated in select families or was a sporadic complication in patients with SLE. We compared the family history of ESRD in 50 patients with SLE complicated by lupus nephritis with 37 controls who had SLE but lacked nephritis after a mean follow-up duration of more than 11 years. The frequency of relatives with ESRD in the lupus nephritis cases was compared with that in controls using Fisher's exact test (significance at P < or = 0.05). Fifty percent (25) of the 50 lupus nephritis patients were black and 50% (25) white, in contrast to 35% (13) and 65% (24) of the 37 lupus non-nephropathy controls, respectively. A first-, second-, or third-degree relative with ESRD was present in 16% (eight) of the 50 lupus nephritis cases and in 0% of the 37 SLE non-nephropathy controls (P = 0.019, Fisher's exact test, two-tail). Twenty-eight percent (seven) of the 25 black patients with lupus nephritis had relatives with ESRD compared with 0% of the 13 black lupus non-nephritis controls (P = 0.07). Only one of the eight relatives with ESRD had SLE or a collagen vascular disease. Lupus nephritis patients and the non-nephritis controls had similar ages (mean +/- SD: 38.5 +/- 10.0 years v 46.6 +/- 11.8 years; P = 0.28), family sizes (6.27 +/- 2.61 first-degree relatives v 6.35 +/- 3.25 first-degree relatives; P = 0.16), and duration of SLE (9.26 +/- 5.94 years v 11.35 +/- 6.43 years; P = 0.60). Familial clustering of ESRD was observed in black patients with SLE who had nephritis. This was unlikely to be related to differences in patient age, family size, or duration of SLE. This data, coupled with the known familial aggregation of ESRD in blacks with hypertensive and diabetic ESRD, supports the contention that genetic factors contribute to the familial clustering. The presence of relatives with etiologies of ESRD other than SLE suggests that there is an inherited susceptibility to progressive renal failure, independent of the etiology of ESRD.

B cells from patients with systemic lupus erythematosus display abnormal antigen receptor-mediated early signal transduction events

To understand the molecular mechanisms that are responsible for the B cell overactivity that is observed in patients with SLE, we have conducted experiments in which the surface immunoglobulin (sIg)-mediated early cell signaling events were studied. The anti-sIgM-mediated free intracytoplasmic calcium ([Ca2+]i) responses were significantly higher in SLE B cells compared with responses of normal individuals and to those of patients with other systemic autoimmune rheumatic diseases. The anti-IgD mAb induced [Ca2+]i responses were also higher in lupus B cells than in controls. The magnitude of anti-sIgM-mediated Ca2+ release from intracellular stores was also increased in B cells from SLE patients compared with normal controls. The amount of inositol phosphate metabolites produced upon crosslinking of sIgM was slightly higher in patients with lupus than in normal controls, although the difference was not statistically significant. In contrast, the degree of anti-sIgM-induced protein tyrosine phosphorylation was obviously increased in lupus patients. Our study demonstrates clearly for the first time that SLE B cells exhibit aberrant early signal transduction events, including augmented calcium responses after crosslinking of the B cell receptor and increased antigen-receptor-mediated phosphorylation of protein tyrosine residues. Because the above abnormalities did not correlate with disease activity or treatment status, we propose that they may have pathogenic significance.

Deficient type I protein kinase A isozyme activity in systemic lupus erythematosus T lymphocytes: II. Abnormal isozyme kinetics

Systemic lupus erythematosus (SLE) T cells exhibit deficient type I protein kinase A (PKA-1) isozyme phosphotransferase activity, resulting in impaired phosphorylation of plasma membrane-associated proteins. To determine the mechanism of this isozyme deficiency, we studied 16 SLE subjects with a mean (+/-1 SD) SLE disease activity index of 16.7 +/- 8.8 and 16 normal controls. Immunoblotting of type I regulatory (RI) subunit protein in SLE and control T cells demonstrated no significant differences in the amount of protein. Analysis of isozyme kinetics in SLE T cells demonstrated a 2.2-fold increase in the Michaelis-Menten constant, a 2.5-fold increase in the apparent association constant for cAMP, a 3.8-fold decrease in the maximal velocity, and a reduction in the mean maximal binding of cAMP to the RI subunit compared with control T cells. Reduction of the Hill coefficient from 1.2 in normal T cells to 0.7 in SLE T cells indicated a loss of positive cooperativity between cAMP binding sites A and B. An increase in the apparent association constant for cAMP signifies relative resistance to cAMP, indicating that higher intracellular concentrations of cAMP are necessary to activate the isozyme. Because the R subunit of PKA is the only intracellular receptor for cAMP, the abnormal isozyme kinetics may account for the deficiency of PKA-I phosphotransferase activity and impaired PKA-I-catalyzed protein phosphorylation observed in SLE T cells. This disordered isozyme function may contribute to the altered signal transduction and observed cellular immune dysfunctions in SLE. Moreover, these altered isozyme kinetics raise the possibility of a structural defect(s) in the RI subunit.

Deficient type I protein kinase A isozyme activity in systemic lupus erythematosus T lymphocytes: II. Abnormal isozyme kinetics

Systemic lupus erythematosus (SLE) T cells exhibit deficient type I protein kinase A (PKA-1) isozyme phosphotransferase activity, resulting in impaired phosphorylation of plasma membrane-associated proteins. To determine the mechanism of this isozyme deficiency, we studied 16 SLE subjects with a mean (+/-1 SD) SLE disease activity index of 16.7 +/- 8.8 and 16 normal controls. Immunoblotting of type I regulatory (RI) subunit protein in SLE and control T cells demonstrated no significant differences in the amount of protein. Analysis of isozyme kinetics in SLE T cells demonstrated a 2.2-fold increase in the Michaelis-Menten constant, a 2.5-fold increase in the apparent association constant for cAMP, a 3.8-fold decrease in the maximal velocity, and a reduction in the mean maximal binding of cAMP to the RI subunit compared with control T cells. Reduction of the Hill coefficient from 1.2 in normal T cells to 0.7 in SLE T cells indicated a loss of positive cooperativity between cAMP binding sites A and B. An increase in the apparent association constant for cAMP signifies relative resistance to cAMP, indicating that higher intracellular concentrations of cAMP are necessary to activate the isozyme. Because the R subunit of PKA is the only intracellular receptor for cAMP, the abnormal isozyme kinetics may account for the deficiency of PKA-I phosphotransferase activity and impaired PKA-I-catalyzed protein phosphorylation observed in SLE T cells. This disordered isozyme function may contribute to the altered signal transduction and observed cellular immune dysfunctions in SLE. Moreover, these altered isozyme kinetics raise the possibility of a structural defect(s) in the RI subunit.

Activation of type I protein kinase A during receptor-mediated human T lymphocyte activation

The experiments reported herein have characterized the signaling pathway leading to stimulation of type I protein kinase A isozyme (PKA-I) activity during the early events of Ag receptor-mediated T cell activation. Inhibitor studies demonstrated that receptor-initiated activation of nonreceptor protein tyrosine kinases, phosphorylation and activation of phospholipase C-gamma 1, and activation of protein kinase C occur temporally and precede PKA-I activation. Bypass of both the TCR/CD3 complex and IL-1R and direct activation of protein kinase C by a phorbol ester can also activate PKA-I. To confirm that PKA-I activation via the TCR/CD3 complex and IL-1R requires antecedent protein tyrosine kinase-catalyzed phosphorylation of phospholipase C-gamma 1, we used wild-type and CD45-deficient (mutant J45.01) Jurkat T cell lines. Unlike wild-type Jurkat T cells, the absence of CD45 tyrosine phosphatase resulted in the failure of receptor-mediated activation of PKA-I activity and of IL-2 mRNA transcription in the mutant J45.01 Jurkat cell line. In conclusion, our data support the concept that a signal derived from ligand binding to both the TCR/CD3 complex and IL-1R receptor mediates rapid activation of the PKA-I isozyme in primary T lymphocytes by sequential activation of an intracellular pathway comprised of CD45 phosphatase/protein tyrosine kinase/polyphosphoinositide/Ca2+/protein kinase C pathway rather than via the conventional surface receptor/stimulatory G protein system.

Activation of type I protein kinase A during receptor-mediated human T lymphocyte activation

The experiments reported herein have characterized the signaling pathway leading to stimulation of type I protein kinase A isozyme (PKA-I) activity during the early events of Ag receptor-mediated T cell activation. Inhibitor studies demonstrated that receptor-initiated activation of nonreceptor protein tyrosine kinases, phosphorylation and activation of phospholipase C-gamma 1, and activation of protein kinase C occur temporally and precede PKA-I activation. Bypass of both the TCR/CD3 complex and IL-1R and direct activation of protein kinase C by a phorbol ester can also activate PKA-I. To confirm that PKA-I activation via the TCR/CD3 complex and IL-1R requires antecedent protein tyrosine kinase-catalyzed phosphorylation of phospholipase C-gamma 1, we used wild-type and CD45-deficient (mutant J45.01) Jurkat T cell lines. Unlike wild-type Jurkat T cells, the absence of CD45 tyrosine phosphatase resulted in the failure of receptor-mediated activation of PKA-I activity and of IL-2 mRNA transcription in the mutant J45.01 Jurkat cell line. In conclusion, our data support the concept that a signal derived from ligand binding to both the TCR/CD3 complex and IL-1R receptor mediates rapid activation of the PKA-I isozyme in primary T lymphocytes by sequential activation of an intracellular pathway comprised of CD45 phosphatase/protein tyrosine kinase/polyphosphoinositide/Ca2+/protein kinase C pathway rather than via the conventional surface receptor/stimulatory G protein system.

Deficient type I protein kinase A isozyme activity in systemic lupus erythematosus T lymphocytes

Systemic lupus erythematosus (SLE) is an autoimmune disorder of indeterminate etiology characterized by a dysfunctional cellular immune response. We have previously identified a metabolic disorder of the adenylate cyclase/cAMP/protein kinase A (AC/cAMP/PKA) pathway characterized by impaired cAMP-inducible, PKA-catalyzed protein phosphorylation in intact T lymphocytes from subjects with severe SLE disease activity. Because this metabolic disorder may contribute to abnormal T cell immune effector functions, we tested the hypothesis that impaired PKA-dependent protein phosphorylation is the result of a PKA isozyme deficiency in SLE T lymphocytes. Compared with healthy and rheumatoid arthritis (RA) controls, subjects with severe SLE activity exhibited reduced PKA-catalyzed phosphorylation of proteins in the T lymphocyte plasma membrane where the type I isozyme of PKA (PKA-I) is predominantly localized. Both silver staining and biosynthetic labeling of membrane-associated proteins with [35S]methionine demonstrated that reduced protein phosphorylation was not due to either an altered distribution of or absence of proteins. Moreover, phosphorylation of SLE membrane-associated proteins with the PKA catalytic (C) subunit showed a similar distribution and extent of phosphorylation compared with membrane proteins from healthy T cells, suggesting that SLE T cell membrane proteins could be phosphorylated. Sequential column chromatography of the type I and type II isozymes of PKA (PKA-I, PKA-II) demonstrated a deficiency of PKA-I isozyme activity. Compared with a ratio of PKA-I to PKA-II activity of 4.2:1 in healthy T cells, the activity ratio in T cells from subjects with severe SLE disease activity was 0.99:1 (P = 0.01, SLE versus healthy controls for PKA-I). The deficient PKA-I activity was associated with a significant increase of free C-subunit activity (P = 0.04, SLE versus healthy controls for C-subunit). T cells from subjects with mild/moderate SLE disease activity also exhibited diminished PKA-I activity, yielding a ratio of PKA-I to PKA-II activity of 2.4:1. By contrast, T cells from RA controls possessed increased PKA-I, PKA-II, and free C-subunit activities compared with healthy controls, resulting in a ratio of PKA-I to PKA-II activity of 3.6:1. We conclude that the reduced PKA-catalyzed protein phosphorylation in the plasma membrane of SLE T cells is the result of deficient PKA-I isozyme activity. This is the first identification of a deficiency of PKA activity in SLE T lymphocytes; the deficiency, resulting in diminished protein phosphorylation, may alter cellular homeostasis, contributing to the cellular immune dysfunctions observed in SLE.

The effect of nonsteroidal anti-inflammatory drugs on cAMP-dependent protein kinase-mediated phosphorylation by human chondrocytes in culture

Although a principal pharmacological action of nonsteroidal anti-inflammatory drugs (NSAIDs) is to blunt eicosanoid synthesis by inhibiting cyclooxygenase, recent evidence indicates that NSAIDs may also interact directly with proteins that control the activity of adenylyl cyclase. Since the only physiological mechanism governing the action of cyclic AMP occurs via activation of its receptor, cyclic AMP-dependent protein kinase (cAMPPk; Kinase A), we determined whether NSAIDs affect intracellular substrate phosphorylation dependent on cAMPPk. The incorporation of 32Pi into cellular proteins that are substrates for cAMPPk was determined in intact human non-arthritic, aged non-arthritic and osteoarthritic chondrocytes in the presence or absence of NSAIDs, namely, sodium meclofenamate, indomethacin, tiaprofenic acid and sodium salicyclate. The transfer of [32P]-ATP was employed to identify phosphoproteins in a membrane fraction prepared from chondrocyte homogenates in the presence or absence of these NSAIDs. The lowest concentration of NSAID was similar to NSAID concentrations achieved during therapy for the arthritides. In intact human chondrocyte strains, activation of cAMPPk by dibutyryl cAMP (dBcAMP) resulted in the phosphorylation of intracellular substrates with an apparent M(r) of 55kD, 42kD, 26kD, 25kD, 22kD, 21.5kD, 20.5kD, and 17kD when examined by autoradiography after 12.5% SDS/PAGE. The NSAIDs augmented or potentiated phosphorylation of these proteins which were cAMPPk-dependent. In the chondrocyte membrane fraction, protein phosphorylation by cAMP was mimicked by isobutylmethylxanthine or by the purified catalytic subunit of bovine cAMPPk. NSAIDs augmented chondrocyte phosphorylation in the chondrocyte membrane fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Early events of human T lymphocyte activation are associated with type I protein kinase A activity

Human T lymphocytes possess both the type I and II isozymes of protein kinase A (PKA). The type I (PKA-I) isozyme is predominantly associated with the plasma membrane, whereas the type II (PKA-II) isozyme is primarily localized to the cytosol. Because the functions of both PKA-I and PKA-II isozymes in the biochemical events of T lymphocyte activation have not been clearly elucidated, we tested the hypothesis that very early events of normal human T lymphocyte activation are mediated by the PKA-I and/or PKA-II isozyme(s). Fresh normal human T cells and a normal human CD4+ T cell line (GK606) activated with anti-CD3-epsilon and recombinant interleukin 1 alpha (rIL-1 alpha) exhibited a peak six- to sevenfold increase of PKA phosphotransferase activity at 5 min that returned to baseline by 60 min. Similarly, both fresh T cells and the T cell line activated by phorbol myristate acetate and ionomycin demonstrated a peak eightfold increase of PKA activity by 15 min that returned toward baseline by 60 min. Chromatographic separation of the PKA isozymes and quantification of phosphotransferase activities after T cell activation by either agonist pair showed preferential activation of the PKA-I isozyme, resulting in a significant reduction in the ratio of PKA-I to PKA-II isozyme activity from 3.1:1-6.2:1 to 1.1:1-3.2:1. PKA-I isozyme activation resulted in the release of free catalytic (C) subunit, an increase in C subunit phosphotransferase activity, and the phosphorylation of T cell plasma membrane-associated proteins, p14, p17, p20, p21, p38, and p48. However, activation of the PKA-I isozyme did not appear to be required for the transcription of IL-2 mRNA, an event necessary for mitosis. These data indicate that ligand-induced T cell activation is associated with rapid activation of the PKA-I, but not PKA-II, isozyme that results in phosphorylation of plasma membrane-associated proteins. The involvement of the PKA-I isozyme during the very early events of T cell activation suggests that this isozyme may be an antigen- or mitogen-stimulated protein kinase.

The effect of circulating serum factors from patients with systemic lupus erythematosus on protein kinase A (PKA) activity and PKA-dependent protein phosphorylation in T lymphocytes

T lymphocytes from subjects with active systemic lupus erythematosus (SLE) exhibit reduced cAMP-inducible, protein kinase A (PKA)-dependent phosphorylation of several intracellular substrates compared with healthy and disease controls. To ascertain whether the persistent T cell activation observed during active SLE can result in impaired PKA-dependent protein phosphorylation, normal T cells were activated in vitro by monoclonal anti-CD3-epsilon antibody and recombinant IL1-alpha (rIL1-alpha) for 24 hr. T cell activation, verified by IL2 mRNA, IL2 receptor-alpha (IL2R-alpha) mRNA, and IL2R-beta mRNA expression, did not diminish cAMP-inducible, PKA-dependent protein phosphorylation. We also tested the hypothesis that circulating factors present in active SLE serum can decrease cAMP-inducible total PKA phosphotransferase activity and PKA-dependent protein phosphorylation in normal T lymphocytes. T cells cultured for 24 hr in medium supplemented with 10% active SLE sera (from subjects who exhibited the defect of PKA-dependent protein phosphorylation) exhibited similar total PKA phosphotransferase activity and substrate phosphorylation as cells cultured in normal AB serum. Moreover, the addition of interferon-alpha (IFN-alpha) and/or immune complexes (IC) did not diminish either total PKA activity or PKA-dependent substrate phosphorylation. Lastly, we found that the defect of PKA-dependent protein phosphorylation in active SLE T cells could not be reversed by culturing the cells in culture medium supplemented with 10% AB serum for 24 hr. In conclusion, (a) deficient cAMP-inducible, PKA-dependent phosphorylation in SLE T cells is not reversible by culturing cells in vitro; (b) there is no evidence to support the concept that serum factors, including IC and IFN-alpha, can induce a defect of PKA-dependent protein phosphorylation in normal T cells.

Human T lymphocyte cAMP-dependent protein kinase: subcellular distributions and activity ranges of type I and type II isozymes

The role of the type I and type II protein kinase A isozymes in the regulation of human T lymphocyte immune effector functions has not been ascertained. To approach this question, we first characterized the distribution and enzyme activities of the type I and type II protein kinase A (PKA) isozymes in normal, human T lymphocytes. T cells possess both type I and type II isozymes with an activity ratio of 5.0:1 +/- 0.71 (mean +/- SD). The type I isozyme associates predominately with the plasma membrane whereas the type II isozyme localizes primarily to the cytosol. Analyses of isozyme activities demonstrated that T cells from approximately one-third of 16 healthy donors exhibited significantly higher type II isozyme activities (higher type II, type IIH) than the remaining donors (lower type II, type IIL) (mean = 605 +/- 75 pmol.min-1.mg protein-1, P less than 0.001). Scatchard analyses of [3H]cAMP binding in the cytosolic fraction demonstrated similar Kd values (type IIH, 1.1 x 10(-7) M; type IIL, 9.0 x 10(-8) M); however, the Bmax (maximal binding) of the type IIH was 400 fmol/mg protein compared to the Bmax of the type IIL of 126 fmol/mg protein. Scatchard analysis of [3H]cAMP binding to the type I isozyme associated with membrane fragments had a Kd of 5.6 x 10(-8) M and a Bmax of 283 fmol/mg protein. Eadie-Hofstee plots of type IIH and type IIL gave a Km and Vmax of 2.3 mg/ml and 1.5 nmol.mg-1.min-1, and 2.1 mg/ml and 1.6 nmol.mg-1.min-1, respectively. The 3.2-fold higher maximal binding of the type II isozyme in one-third of healthy donors may reflect a greater amount of isozyme protein. The compartmentalization of type I PKA isozyme to the plasma membrane and type II PKA isozyme to the cytosol may serve to localize the isozymes to their respective substrates in T lymphocytes.

Defective cAMP-dependent phosphorylation of intact T lymphocytes in active systemic lupus erythematosus

The present study was undertaken to establish whether cAMP-dependent phosphorylation of endogenous substrates is impaired in T lymphocytes from subjects with active systemic lupus erythematosus (SLE). In normal human T lymphocytes, the cell-permeable cAMP analog, N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate, induced phosphorylation of substrates with molecular masses of 17.5, 23/25, 33.5 kDa on one-dimensional SDS/PAGE. Maximal phosphorylation occurred at 60 min. In contrast to healthy T cells, the extent of substrate phosphorylation achieved in active SLE T cells (n = 8) was only 15% at 60 min in the 17.5-kDa substrate, 21% in the 23/25-kDa substrate, and 9% in the 33.5-kDa substrate. The rheumatic disease controls (rheumatoid arthritis; primary Sjögren syndrome; n = 8) exhibited a mean 72%, 124%, and 85%, respectively, of phosphorylation observed in healthy T cells. Because the only known mechanism by which cAMP acts is via cAMP-dependent protein kinase (protein kinase A), these data raise the possibility of a defect at the level of this kinase in SLE T lymphocytes.

UVB radiation and human monocyte accessory function: differential effects on pre-mitotic events in T-cell activation

Purified T lymphocytes fail to proliferate in response to antigenic and mitogenic stimuli when cultured in the presence of accessory cells that have been exposed in vitro to sublethal doses of UVB radiation. Because proliferation represents a final stage in the T-cell activation process, the present study was conducted to determine whether T cells were able to progress through any of the pre-mitotic stages when UVB-irradiated monocytes were used as model accessory cells. In these experiments, monoclonal anti-CD3 antibodies were employed as the mitogenic stimulus. Culture of T cells with UVB-irradiated monocytes did allow the T cells to undergo an increase in intracellular free calcium, which is one of the first steps in the activation sequence. The T cells expressed interleukin-2 receptors, although at a reduced level. However, T cells failed to produce interleukin-2 above background levels when they were placed in culture with monocytes exposed to UVB doses as low as 50 J/m2. Incubation of T cells with UVB-irradiated monocytes did not affect the subsequent capacity of T cells to proliferate, since they developed a normal proliferative response in secondary culture when restimulated with anti-CD3 antibodies and unirradiated monocytes. These studies indicate that T lymphocytes become partially activated when cultured with UVB-irradiated monocytes and mitogenic anti-CD3 monoclonal antibodies. In addition, they suggest that interleukin-2 production is the T-cell activation step most sensitive to inhibition when UVB-irradiated monocytes are employed as accessory cells.

Association of cytoskeletal re-organization with capping of the complement decay-accelerating factor on T lymphocytes

Recent studies have identified cell-associated proteins that are membrane anchored by glycosyl-inositol-phospholipid structures but the biologic implications of this mode of membrane attachment are incompletely understood. Among proteins anchored in this way is the decay-accelerating factor (DAF), a complement (C) regulatory factor that functions on blood cell surfaces to prevent autologous C attack. As one approach to investigate the functional consequences of glycosyl-inositol-phospholipid-anchoring of DAF in T lymphocytes, the effects of crosslinking surface DAF molecules were compared to those of crosslinking conventionally by anchored cluster of differentiation (CD) proteins. Upon incubation with anti-DAF mAb and anti-murine IgG, DAF re-distributed to a pole of the cell with a t1/2 at 37 degrees C of 4.4 min as compared to t1/2 of 3.5 to 7 min for CD3, CD4, and CD8. Re-distribution of DAF occurred independently of CD2, CD3, CD4, or CD8. Anti-DAF immunoprecipitates of membrane extracts of cells chemically cross-linked with dithiobis(succinimidylpropionate) contained only monomeric DAF. Immunofluorescent staining demonstrated clustered actin, tubulin, and vimentin beneath the capped DAF protein. Pre-treatment of cells with colchicine or 8-azidoadenosine 3',5'-cyclic phosphate, but not lumicolchicine, resulted in reduction of the t1/2 for DAF to 1 to 2.6 min. Conversely, treatment of cells with cytochalasins B or D completely blocked DAF capping. The results indicate that, upon cross-linking, glycosyl-inositol-phospholipid-anchored DAF molecules undergo capping similar to conventionally anchored CD molecules and that DAF capping is associated with cytoskeletal reorganization.

Association of cytoskeletal re-organization with capping of the complement decay-accelerating factor on T lymphocytes

Recent studies have identified cell-associated proteins that are membrane anchored by glycosyl-inositol-phospholipid structures but the biologic implications of this mode of membrane attachment are incompletely understood. Among proteins anchored in this way is the decay-accelerating factor (DAF), a complement (C) regulatory factor that functions on blood cell surfaces to prevent autologous C attack. As one approach to investigate the functional consequences of glycosyl-inositol-phospholipid-anchoring of DAF in T lymphocytes, the effects of crosslinking surface DAF molecules were compared to those of crosslinking conventionally by anchored cluster of differentiation (CD) proteins. Upon incubation with anti-DAF mAb and anti-murine IgG, DAF re-distributed to a pole of the cell with a t1/2 at 37 degrees C of 4.4 min as compared to t1/2 of 3.5 to 7 min for CD3, CD4, and CD8. Re-distribution of DAF occurred independently of CD2, CD3, CD4, or CD8. Anti-DAF immunoprecipitates of membrane extracts of cells chemically cross-linked with dithiobis(succinimidylpropionate) contained only monomeric DAF. Immunofluorescent staining demonstrated clustered actin, tubulin, and vimentin beneath the capped DAF protein. Pre-treatment of cells with colchicine or 8-azidoadenosine 3',5'-cyclic phosphate, but not lumicolchicine, resulted in reduction of the t1/2 for DAF to 1 to 2.6 min. Conversely, treatment of cells with cytochalasins B or D completely blocked DAF capping. The results indicate that, upon cross-linking, glycosyl-inositol-phospholipid-anchored DAF molecules undergo capping similar to conventionally anchored CD molecules and that DAF capping is associated with cytoskeletal reorganization.

Control of human T-lymphocyte interleukin-2 production by a cAMP-dependent pathway

Cyclic AMP has long been proposed to be the intracellular second messenger that conveys the inhibitory signal for T-cell activation and clonal T-cell proliferation. The present study further explores the mechanism by which the cAMP pathway regulates human T-lymphocyte interleukin-2 (IL-2) production and T-cell blastogenesis. Activation of adenylate cyclase, inhibition of cAMP-dependent phosphodiesterase, or the direct addition of the cell-permeable cAMP analog, 8-N3-cAMP, increased occupancy of intracellular cAMP receptors, inhibited IL-2 production, and reduced T-cell proliferation. However, inhibition of cAMP-dependent protein phosphorylation by N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8), a cell-permeable inhibitor of cyclic nucleotide-dependent protein kinase, partially restored IL-2 production. Our data support the conclusion that the cAMP pathway conveys an inhibitory signal for IL-2 production and T-cell proliferation via an integral protein phosphorylation step.

Characterization of the human T lymphocyte adenosine receptor: comparison of normal and systemic lupus erythematosus cells

To determine whether a defect in the T cell response to adenosine exists at the level of the adenosine receptor in systemic lupus erythematosus (SLE) we measured the binding affinity and maximum binding of T cell membranes from both normal and SLE T cells by utilizing radiolabeled adenosine ligands. Normal T lymphocyte membranes possess a single class of [3H]5-N-ethylcarboxamide adenosine binding sites with a Kd of 0.61 microM, a Bmax of 23.5 pmol/mg protein, and a Hill coefficient of 0.98, which indicates the presence of noncooperative sites. In contrast, T cell membranes do not bind significant amounts of either [3H]cyclohexyladenosine or [3H]phenylisopropyladenosine. These data indicate that T lymphocyte membranes have only A2, and not A1, adenosine receptors. Similarly, T cells from both active and inactive SLE subjects also express only A2 receptors with a Kd of 0.93 microM, a Bmax of 20.4 pmol/mg protein, and a Hill coefficient of 0.85, which is consistent with the presence of noncooperative sites. There is no difference in the on-rate, affinity, or density of T cell A2 receptors from active SLE patients, inactive SLE patients, or healthy controls. We conclude that T lymphocytes from both healthy and SLE subjects express A2, but not A1, receptors. Thus, the inability of SLE T cells to respond to adenosine does not reflect a decreased density of A2 (stimulatory) receptors, diminished A2 receptor binding, or an increased affinity or number of A1 (inhibitory) adenosine receptors. These observations support the conclusion that the defect in the T cell cAMP-dependent pathway may occur at a point distal to the adenosine receptor.

Mobility of the human T lymphocyte surface molecules CD3, CD4, and CD8: regulation by a cAMP-dependent pathway

The present study was undertaken to determine whether a cAMP pathway mediates the mobility of CD3, CD4, and CD8 within the membrane. Crosslinking CD3, CD4, and CD8 with monoclonal antibody and anti-antibody induced rapid accumulation of intracellular cAMP, occupancy of cAMP receptors, and was temporally associated with the mobilization and directed movement of these molecules to a pole of the cell. This capping process could be partially inhibited in a dose-dependent manner by treatment of T cells with 2',5'-dideoxyadenosine, a ribose-modified adenosine analogue that binds to the P site of the catalytic subunit of adenylate cyclase and reduces adenylate cyclase activity. Furthermore, inhibition of cAMP-dependent endogenous phosphorylation of 17.5-kDa, 23/25-kDa, and 33.5-kDa bands in intact T cells by N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide, a cell-permeable inhibitor of cyclic nucleotide-dependent protein kinase, blocked the capping event. Data support the conclusion that crosslinking of CD3, CD4, and CD8 activates a cAMP-dependent pathway that mediates the mobilization and directed movement of these molecules. cAMP-dependent protein phosphorylation is an integral step leading to the capping process.

Impaired mobility of human T lymphocyte surface molecules during inactive systemic lupus erythematosus. Relationship to a defective cAMP pathway

The T lymphocytes of patients with active systemic lupus erythematosus (SLE) exhibit impaired capping of the surface molecules CD3, CD4, and CD8 and a defective cAMP-dependent pathway. Since the mobility of these molecules is regulated in part by cAMP, we sought to determine whether there is a specific defect(s) along the T cell cAMP pathway that contributes to the persistent capping disorder observed during inactive SLE. The data suggest that a defect may exist at the level of cAMP-dependent protein kinase activation or at a point distally. We propose that a disorder of cAMP-dependent protein kinase activity might account for the defect of capping observed in both the CD3, CD4 (helper/inducer) and CD3, CD8 (suppressor) subsets observed in SLE.

Intact proteoglycan is a polyclonal activator of murine B-lymphocytes

Destruction of articular cartilage is the hallmark of both inflammatory and degenerative arthritides. Since degradation of cartilage results in the release of proteoglycan (PG) monomers and fragments into the synovial fluid, the present study was initiated to determine whether hyaline cartilage PG can induce a cellular immune response. Nonimmune spleen cells obtained from A/St and C57Bl/6 mice were cultured with a crude extract of bovine nasal cartilage, a PG aggregate fraction, PG monomer or degraded PG monomer for varying time periods. Only intact PG monomer induced a proliferative response which peaked at day 2. The responding cell was a B-lymphocyte which did not require T-helper cell activity. Our results suggest that intact PG monomer is a polyclonal activator of B-lymphocytes.

Role of adenylate cyclase in human T-lymphocyte surface antigen capping

Our recent studies indicated that capping of T3, T4 and T8 surface antigens on human T lymphocytes is augmented by interaction of adenosine with a purinergic receptor. We suggested that the T-cell capping process was mediated by an adenylate cyclase-coupled purinergic receptor that resulted in the generation of cAMP and occupancy of cAMP receptors. The present study was undertaken to examine whether activation of adenylate cyclase in the absence of purinergic stimulation is sufficient to regulate surface antigen capping. Treatment of T lymphocytes with forskolin or cholera toxin caused activation of adenylate cyclase and occupancy of intracellular types I and II regulatory subunits of protein kinase by cAMP, as demonstrated by photoaffinity labeling with [8-3H]N3-cAMP. Such treatment augmented the rate of capping of the T3, T4, and T8 antigens, which resulted in a significant decrement in the elapsed time to half-maximal capping of each antigen. These observations support the proposition that the normal T-lymphocyte capping mechanism of both T3+, T4+ (inducer/helper) and T3+, T8+ (suppressor) subsets can be augmented by activation of adenylate cyclase.

Effect of anti-T cell autoantibodies from systemic lupus erythematosus sera upon T lymphocyte functions

This study was undertaken to establish whether IgM and IgG anti-T cell autoantibodies obtained from sera of patients with active systemic lupus erythematosus, impair normal T lymphocyte functions. Two in vitro models of T cell function were examined: (a) the capacity of cells to cap, endocytose, and regenerate the T3, T4, and T8 surface antigens; and (b) the adenosine-induced T4----T8 phenotype switch. The results demonstrated that autoantibody neither impaired the capping process, nor impeded the phenotypic switch. Thus, bound anti-T cell autoantibodies do not appear to interfere with these specific T lymphocyte functions and cannot directly account for either the impaired T cell capping mechanism or the block in adenosine-induced phenotype switch observed during active systemic lupus erythematosus.

Secretion of an articular cartilage proteoglycan-degrading enzyme activity by murine T lymphocytes in vitro

Destruction of articular cartilage is the hallmark of inflammatory arthritides. Enzymes elaborated by mononuclear cells infiltrating the synovium mediate, in part, the degradation of the cartilage extracellular matrix. Since mononuclear cells are the dominant cell type found in chronic inflammatory synovitis, we investigated whether interaction of immune mononuclear cells with antigen initiated the synthesis and secretion of a proteoglycan-degrading enzyme activity. Proteoglycan-degrading enzyme activity was monitored by the capacity of murine spleen cell conditioned medium to release [3H]serine/35SO4 incorporated into rabbit cartilage proteoglycan monomer fraction (A1D1), and by the relative change in specific viscosity of bovine nasal cartilage proteoglycan monomer. The results demonstrated that both virgin and immune mononuclear cells spontaneously generated proteoglycan-degrading enzyme activity and that cellular activation and proliferation induced by the antigen keyhole limpet hemocyanin or the mitogen phytohemagglutinin was not required. Kinetic studies demonstrated stable release of the enzyme activity over 72 h. Cell separation studies showed that T lymphocytes, a thymoma line, and macrophages separately produced proteoglycan-degrading enzyme activity. The enzyme activity has been partially characterized and appears to belong to a class of neutral pH metal-dependent proteinases. These observations, the first to demonstrate that T lymphocytes secrete an enzyme capable of degrading cartilage proteoglycan, raise the possibility that this enzyme activity contributes to cartilage extracellular matrix destruction in vivo. Moreover, these data support the conclusion that production of this enzyme by T lymphocytes is independent of an antigen-specific stimulus.

Regulation of human T lymphocyte surface antigen mobility by purinergic receptors

The present study was undertaken to establish whether the capping mechanism of normal human T lymphocytes is regulated by a purinergic receptor. Interaction of T lymphocytes with adenosine significantly increased the mobility of the T3, T4, and T8 surface antigens. This enhanced rate of capping was reflected by a significant decrement in the time intervals to achieve half-maximal capping. T lymphocytes preincubated with theophylline or isobutylmethylxanthine did not exhibit accelerated capping or a decrease in the time required for half-maximal capping in response to adenosine, suggesting that these agents inhibited the binding of adenosine to its receptor. A role for a cAMP-dependent pathway in capping was suggested by the observation that the phosphodiesterase inhibitor RO-201724 caused a decrease in the concentration of adenosine required to accelerate the capping process. Moreover, exposure of T lymphocytes to the cyclic nucleotide derivatives 8-N3-cAMP and 8-Br-cAMP mimicked the effect of adenosine, significantly reducing the time to half-maximal capping. Photoaffinity labeling of intracellular cAMP receptors with 32P-8-N3-cAMP indicated that adenosine caused occupancy of the receptors. This effect of adenosine was inhibited by theophylline, a known purinergic receptor blocker. The data support the concept that the T cell capping mechanism is mediated by an adenylate cyclase-coupled purinergic receptor that activates a cAMP-dependent pathway, and that this pathway is functional in the T3+, T4+, (inducer) and T3+, T8+ (suppressor) subsets.

Regulation of human T lymphocyte surface antigen mobility by purinergic receptors

The present study was undertaken to establish whether the capping mechanism of normal human T lymphocytes is regulated by a purinergic receptor. Interaction of T lymphocytes with adenosine significantly increased the mobility of the T3, T4, and T8 surface antigens. This enhanced rate of capping was reflected by a significant decrement in the time intervals to achieve half-maximal capping. T lymphocytes preincubated with theophylline or isobutylmethylxanthine did not exhibit accelerated capping or a decrease in the time required for half-maximal capping in response to adenosine, suggesting that these agents inhibited the binding of adenosine to its receptor. A role for a cAMP-dependent pathway in capping was suggested by the observation that the phosphodiesterase inhibitor RO-201724 caused a decrease in the concentration of adenosine required to accelerate the capping process. Moreover, exposure of T lymphocytes to the cyclic nucleotide derivatives 8-N3-cAMP and 8-Br-cAMP mimicked the effect of adenosine, significantly reducing the time to half-maximal capping. Photoaffinity labeling of intracellular cAMP receptors with 32P-8-N3-cAMP indicated that adenosine caused occupancy of the receptors. This effect of adenosine was inhibited by theophylline, a known purinergic receptor blocker. The data support the concept that the T cell capping mechanism is mediated by an adenylate cyclase-coupled purinergic receptor that activates a cAMP-dependent pathway, and that this pathway is functional in the T3+, T4+, (inducer) and T3+, T8+ (suppressor) subsets.