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.

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.

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.

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.

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.

Evaluation of genotoxic potential of vincristine from multiple parameters

The genotoxic potential of vincristine is assessed by in vivo and in vitro cytogenetic assays on two test systems using multiple parameters. In in vivo experiments it was administered intraperitoneally to Swiss albino mice at doses computed on a surface area basis to lie within the therapeutic range. The parameters employed include screening of chromosome mutational activity in bone marrow and meiotic cells for periods covering one spermatogenetic cycle, in vivo SCE analysis and sperm head abnormality assay. In vitro studies included conventional scoring for chromosome mutations from human leucocyte cultures following administration of the drug at doses within the therapeutic range on the basis of blood volume. Strict controls were employed in both test systems. The data were treated by appropriate statistical tests to evaluate their validity. The results of in vivo experiments on somatic as well as meiotic test systems reveal a lack of clastogenic action of the compound. Both sexes respond in an identical fashion regarding this activity. The SCE analysis supports the in vivo nonclastogenic action of vincristine. Total univalents significantly seen with the highest dose after 1 and 2 weeks must be considered as being important as they can lead to aneuploidy. Evidence is adduced from sperm head abnormality assay that the drug induces point mutations. The results from in vitro test system indicate a positive chromosome mutational property. This is substantiated by results of in vitro SCE analysis. A comparison of data from in vivo and in vitro test systems suggests that a metabolic conversion of the compound in the former might render it innocuous for expressing the chromosome mutational activity. They also point out that vincristine evokes a differential clastogenic response in the two test systems despite bringing about an anaphase arrest commonly in both by acting on cytokinesis.