Coupling of viral membrane proteins to phosphatidylinositide signalling system.

C6 rat glioma cells persistently infected with subacute sclerosing panencephalitis virus (C6/SSPE) were treated with measles antiserum and purified anti-measles IgG. This stimulated phosphoinositide breakdown and an increase in inositol phosphates. In uninfected C6 cells, however, only fetal calf serum (FCS), but not measles antiserum could induce inositol polyphosphate production.

Diadenosine tetraphosphate (Ap4A) is compartmentalized in nuclei of mammalian cells.

The intracellular compartmentation of Ap4A in various growth and cell-cycle stages in mammalian cells was studied by applying a non-aqueous extraction procedure for cell nuclei. In both slowly and in exponentially growing Ehrlich ascites tumour cells from random cultures, more than 75% of the whole cellular Ap4A content is localized in the nuclei. In G1 and early S-phase cells of synchronized baby hamster kidney (BHK) fibroblast cultures, approx. 90% of the intracellular Ap4A pool is confined to the nuclear compartment. In contrast, Ap4A is distributed to nearly equal amounts between cytoplasm and nuclei during mid-S phase. After transition through the S-phase, increasing proportions of Ap4A (78% 18 h and 96% 22 h after serum replenishing, respectively) are again localized in the nuclear compartment.

Zinc as a second messenger of mitogenic induction. Effects on diadenosine tetraphosphate (Ap4A) and DNA synthesis.

DNA synthesis and adenosine(5')tetraphosphate(5')adenosine (Ap4A) levels decrease in cells treated with EDTA. The inhibitory effect of EDTA can be reversed with micromolar amounts of ZnCl2. ZnCl2 in micromolar concentrations also inhibits Ap4A hydrolase and stimulates amino acid-dependent Ap4A synthesis, suggesting that Zn2+ is modulating intracellular Ap4A pools. Serum addition to G1-arrested cells enhances uptake of Zn, whereas serum depletion leads to a fivefold decrease of the rates of zinc uptake. These results are discussed by regarding Zn2+ as a putative 'second messenger' of mitogenic induction and Ap4A as a possible 'third messenger' and trigger of DNA synthesis.

High diadenosine tetraphosphate (Ap4A) level in germ cells and embryos of sea urchin and Xenopus and its effect on DNA synthesis.

Ap4A levels in sperms, eggs and different developmental stages of sea urchin (Psammechinus miliaris) and (Xenopus laevis) were determined by a method based on ATP measurement with luciferin/luciferase after splitting diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) into ATP and AMP. Appreciable storage pools of Ap4A were found in unfertilized eggs of Psammechinus and Xenopus as well as in sea urchin sperms. The actual Ap4A concentration of 28 microM in sperm represents the highest Ap4A level so far observed in eukaryotic cells. Upon fertilization an instant onset of de novo synthesis of Ap4A was demonstrated. Ap4A levels during early embryogenesis of P. miliaris and X. laevis (2.5-4 microM) are higher than those in exponentially growing mammalian culture cells and mammalian fetuses. Microinjection of Ap4A into unfertilized eggs of Psammechinus miliaris caused a 3-7 fold increase of DNA synthesis in comparison with mock-injected eggs.

High diadenosine tetraphosphate (Ap4A) level at initiation of S phase in the naturally synchronous mitotic cycle of Physarum polycephalum.

Levels of the diadenosine tetraphosphate Ap4A are high during exponential growth of Physarum, decrease during encystment (spherulation) and increase again during excystment. Consistently, a rapid 8-30-fold increase in Ap4A level occurs at entry into S phase of the mitotic cycle and is maintained during the first half of genome replication. The elevated Ap4A level depends significantly on ongoing DNA replication and is completely sensitive to the protein synthesis inhibitor cycloheximide administered either before or after initiation of S phase.

Drastic rise of intracellular adenosine(5')tetraphospho(5')adenosine correlates with onset of DNA synthesis in eukaryotic cells.

An assay of adenosine(5')tetraphospho(5')adenosine (Ap4A), based on the luciferin/luciferase method for ATP measurement, was developed, which allows one to determine picomolar amounts of unlabeled Ap4A in cellular extracts. In eukaryotic cells this method yielded levels of Ap4A varying from 0.01 microM to 13 microM depending on the growth, cell cycle, transformation, and differentiation state of cells. After mitogenic stimulation of G1-arrested mouse 3T3 and baby hamster kidney fibroblasts the Ap4A pools gradually increased 1000-fold during progression through the G1 phase reaching maximum Ap4A concentrations of about 10 microM in the S phase. Quiescent 3T3 cells reach a high level of Ap4A (1 microM) in a 'committed' but prereplicative state if exposed to an external mitogenic stimulant (excess of serum) and simultaneously to a synchronizer which inhibits entry into the S phase (hydroxyurea). When the block for DNA replication was removed at varying times after removal of the stimulant decay of commitment to DNA synthesis was found correlated with a shrinkage of the Ap4A pool. Cells lacking a defined G1 phase (V79 lung fibroblasts, Physarum) possess a constitutively high base level of Ap4A (about 0.3 microM) even during mitosis. From this high level, Ap4A concentration increases only about tenfold during the S phase. Temperature-down-shift experiments, using chick embryo cells infected with transformation-defective temperature-sensitive viral mutants(td-ts), have shown that the expression of the transformed state at 35 degrees C is accompanied by a tenfold increase of the cellular Ap4A pool. Treatment of exponentially growing human cells with interferon leads, concomitantly with an inhibition of DNA syntheses, to a tenfold decrease in intracellular Ap4A levels within 20 h. The possibility of Ap4A being a 'second messenger' of cell cycle and proliferation control is discussed in the light of these results and those reported previously demonstrating that Ap4A is a ligand of mammalian DNA polymerase alpha, triggers DNA replication in quiescent mammalian cells and is active in priming DNA synthesis.

The effect of native and single stranded DNA on the platelet release reaction. Enhancement of aggregated IgG-induced serotonin release.

Native (n) but not single stranded (ss) DNA was found to induce release of 3H-serotonin (5-HT) from platelets of the majority of normal individuals. However, ssDNA markedly enhanced 5-HT release induced by heat-aggregated IgG (aggIgG), while less enhancement was seen using nDNA. Similar enhancement was produced by polyinosinic acid but not by polyinosinic:polycytidylic acid. The ability of ssDNA to potentiate aggIgG-induced 5-HT release seemed specific for aggIgG, since no effect on ADP or epinephrine-induced release was observed and thrombin-induced release was inhibited. In contrast, nDNA in high concentrations (100 micrograms/ml) potentiated ADP, epinephrine, and thrombin-induced 5-HT release. These results suggest that ss-and nDNA may interact with platelets by different mechanisms and provide a means by which DNA, released at sites of tissue injury, could modulate the role of platelets in the inflammatory response. The ability of DNA to enhance the aggIgG-induced platelet release reaction may be important in immune complex diseases such as systemic lupus erythematosus.

Familial systemic lupus erythematosus: immunogenetic studies in eight families.

Familial SLE provides a unique opportunity to study the relationships of previously associated genetic factors (HLA and complement component deficiencies) to the occurrence of SLE, other immune disorders, and autoantibodies in families. Thus, eight families containing two or more affected members with SLE (n = 22) and their relatives (n = 40) were examined for HLA genotypes, complement components and autoantibodies. Among the 40 non-SLE relatives, 7 (18%) had other immune diseases, including thyroid disease in 2, rheumatoid arthritis in 2, ITP in 2, and Henoch-Schönlein purpura in one. This compared to 4 of the 22 SLE patients (also 18%) of whom 3 had thyroid disease and one PSS. Eleven non-SLE relatives (28%) had ANA, which was in high-titer in 5 (13%). Eleven (28%) had antibodies to ssDNA, and one had a BFP. Only the SLE patients had antidsDNA, Ro(SSA), Sm or nRNP. A heterozygous C2 deficiency (C2D) was found in only one of the seven kindreds studied, and followed an A25, B18 DR7 haplotype. Heterozygous C2D, however, was inherited by only one of three family members with SLE. HLA-DR2 occurred in 36% and DR3 in 36% of SLE patients, which was not significantly different from either non-SLE family members or unrelated local controls. Sib pair analysis of seven sets presented here and seven from two published reports, demonstrated only random distribution with SLE. Similarly, other immune disorders and autoantibodies followed no consistent HLA haplotypes or DR specificities. Interestingly, DR2 and/or DR3 were found in five of the six patients (83%) having anti-ro(SSA) antibodies (p = NS). These data strongly suggest that genetic factors (other than HLA and complement component deficiencies) and/or environmental factors are necessary for the expression of SLE and other immune abnormalities in lupus families.

Mechanisms of abnormal platelet aggregation in systemic lupus erythematosus.

Platelet aggregation was measured in 14 patients with systemic lupus erythematosus (SLE) and 13 normal controls. Ten SLE patients (group I) showed decreased responsiveness to collagen, while aggregation was normal in 4 (group II). Group I patients also responded poorly to epinephrine. Platelets from SLE patients did not differ from controls in the production of malondialdehyde in response to N-ethylmaleimide, suggesting intact prostaglandin synthetic pathways. However, a significant decrease (P less than 0.005) in platelet levels of the dense granule constituent, serotonin, was noted in group I SLE patients. Treatment of SLE platelet-rich plasma with deoxyribonuclease (DNase) resulted in enhancement of collagen-induced aggregation in 4 group I SLE patients, but not in 1 group II or 8 normal individuals. These results suggest that defective aggregation in SLE platelets may be partially related to a storage pool deficiency state. However, the ability to restore aggregation to collagen by digestion of platelet-rich plasma with DNase indicates that the defect is reversible and that it is perhaps mediated by plasma or platelet-associated DNA.

Necrotizing arteritis and spinal subarachnoid hemorrhage in Sjögren syndrome.

A 37-year-old woman with primary Sjögren syndrome developed mixed cryoglobulinemia and systemic vasculitis. Subarachnoid hemorrhage occurred as a result of necrotizing anterior spinal arteritis. Although rarely seen in mixed cryoglobulinemia, central nervous system complications have recently been documented in Sjögren syndrome. The patient's serum contained antibodies to the Ro(SSA) cytoplasmic antigen, and these antibodies were concentrated in the cryoglobulin fraction. Anti-Ro(SSA) antibodies are associated with the occurrence of vasculitis in patients with Sjögren syndrome, which suggests that the spinal arteritis and subarachnoid hemorrhage in this patient may have been directly related to the underlying connective tissue disorder.

Decreased platelet serotonin levels in systemic lupus erythematosus.

Platelet serotonin levels were measured in 41 patients with systemic lupus erythematosus (SLE) and 36 normal controls. SLE patients had significantly lower mean serotonin levels (243 +/- 131 versus 414 +/- 175 ng/10(9) platelets, P less than 0.001); the lowest levels occurred in those patients with active disease. No differences in mean platelet serotonin levels were found when we compared patients with or without a history of renal disease, thrombocytopenia, or neuropsychiatric involvement. Decreased release of platelet granule constituents, as measured by plasma levels of the alpha-granule protein, beta-thromboglobulin.

Survivorship in systemic lupus erythematosus: effect of antibody to extractable nuclear antigen.

The course of 81 patients with systemic lupus erythematosus (SLE) who had sera tested for antibody to extractable nuclear antigen (ENA) was studied to determine the effect of the presence of antiENA antibody on survivorship. There were no differences in percent survival between the patients with and without antibody to ENA or those with and without antibody to the ribonucleoprotein (RNP) component of ENA. We conclude that there is no prognostic advantage to the presence of either antiENA or antiRNP antibody in patients with SLE.