Band 382, Heft 10

The viral interleukin-10 promoter (vIL-10p), overlapping the rep* element in the EpsteinBarr virus (EBV) genome, is a promoter element active mostly in the late phase of the lytic cycle and immediately upon infection of B cells. rep* was, through transfection experiments with small plasmids, characterised as a cis element supporting oriP replicative function. In this study, in vivo protein binding and CpG methylation at rep*/vIL-10p were analysed in five cell lines that harbour strictly latent EBV genomes. Contrary to the invariably unmethylated dyad symmetry element (DS) of oriP, rep*/vIL-10p was highly methylated and showed only traces of protein binding in all examined cell lines. This result is in agreement with vIL-10p being an inactive promoter of EBV genomes, and makes it less likely that rep* functions as a replicative element of latent EBV genomes.

Ribonuclease P, the ubiquitous endonuclease required for generating mature tRNA 5 ends, is a ribonucleoprotein in most organisms and organelles, with the exception of mitochondria and chloroplasts of multicellular organisms. The cyanelle of the primitive alga Cyanophora paradoxa is the only photosynthetic organelle where the ribonucleoprotein nature of this enzyme has been functionally proven. tmRNA is another highly structured RNA: it can be aminoacylated with alanine, which is then incorporated into a tag peptide encoded on the same RNA molecule. This dualfunction RNA has been found in bacteria, and its gene is also present in mitochondria and plastids from primitive organisms. Since nothing is known about the expression of this RNA in organelles, we have performed processing studies and determined the promoter of cyanelle pretmRNA. This RNA is transcribed as a precursor molecule in vivo. Synthetic transcripts of cyanelle pretmRNA, including or lacking the mature 3 CCAend, are efficiently and correctly processed in vitro by bacterial RNase P ribo and holoenzymes and by the homologous cyanelle RNase P. In addition to these experimental data, we propose a novel secondary structure model for this organellar tmRNA, which renders it more similar to its bacterial counterpart.

tRNA CCAtermini are generated and maintained by tRNA nucleotidyltransferases. Together with poly(A) polymerases and other enzymes they belong to the nucleotidyltransferase superfamily. However, sequence alignments within this family do not allow to distinguish between CCAadding enzymes and poly(A) polymerases. Furthermore, due to the lack of sequence information about animal CCAadding enzymes, identification of corresponding animal genes was not possible so far. Therefore, we looked for the human homolog using the bakers yeast tRNA nucleotidyltransferase as a query sequence in a BLAST search. This revealed that the human gene transcript CGI-47 (#AF151805) deposited in GenBank is likely to encode such an enzyme. To identify the nature of this protein, the cDNA of the transcript was cloned and the recombinant protein biochemically characterized, indicating that CGI-47 encodes a bona fide CCAadding enzyme and not a poly(A) polymerase. This confirmed animal CCAadding enzyme allowed us to identify putative homologs from other animals. Calculation of a neighborjoining tree, using an alignment of several CCAadding enzymes, revealed that the animal enzymes resemble more eubacterial ones than eukaryotic plant and fungal tRNA nucleotidyltransferases, suggesting that the animal nuclear cca genes might have been derived from the endosymbiotic progenitor of mitochondria and are therefore of eubacterial origin.

New analogs of dUMP, dTMP and 5-fluorodUMP, including the corresponding 5thiophosphates (dUMPS, dTMPS and FdUMPS), 5dithiophosphates (dUMPS2, dTMPS2 and FdUMPS2), 5Hphospho nates (dUMPH, dTMPH and FdUMPH) and 5S thiosulfates (dUSSO3, dTSSO3 and FdUSSO3), have been synthesized and their interactions studied with highly purified mammalian thymidylate synthase. dUMPS and dUMPS2 proved to be good substrates, and dTMPS and dTMPS2 classic competitive inhibitors, only slightly weaker than dTMP. Their 5-fluoro congeners behaved as potent, slowbinding inhibitors. By contrast, the corresponding 5Hphosphonates and 5Sthiosulfates displayed weak activities, only FdUMPH and FdUSSO3 exhibiting significant interactions with the enzyme, as weak competitive slowbinding inhibitors versus dUMP. The pHdependence of enzyme timeindependent inhibition by FdUMP and FdUMPS was found to correlate with the difference in pKa values of the phosphate and thiophosphate groups, the profile of FdUMPS being shifted (~1 pH unit) toward lower pH values, so that binding of dUMP and its analogs is limited by the phosphate secondary hydroxyl ionization. Hence, together with the effects of 5Hphosphonate and 5Sthiosulfate substituents, the much weaker interactions of the nucleotide analogs (35 orders of magnitude lower than for the parent 5phosphates) with the enzyme is further evidence that the enzymes active center prefers the dianionic phosphate group for optimum binding.

In this study we show that activation of p38MAPKby IL-6 acts as an inhibitory signal on IL-6-mediated activation of STAT and the α2-macroglobulin promoter. We analyzed the role of MKK6/p38MAPKfor IL-6 signal transduction and transcriptional activation of the suppressor of cytokine signaling (SOCS) 3 promoter. Pretreatment of cells with the p38MAPKspecific inhibitor SB202190 downregulates the induction of SOCS3-mRNA expression by IL-6. Accordingly, overexpression of a constitutively active MKK6 in HepG2 cells enhanced basal activity or IL-6-induced transcriptional activation of a SOCS3 promoter reporter construct, whereas overexpression of a dominant negative mutant of MKK6 downregulated the IL-6-mediated activation of the SOCS3 promoter. These data indicate that p38MAPKactivation is crucial for IL-6-induced SOCS3 expression and downregulation of IL-6-mediated gene induction.

The brainspecific GDP/GTP exchange factor collybistin interacts with the receptoranchoring protein gephyrin and activates the Rholike GTPase Cdc42, which is known to regulate actin cytoskeleton dynamics. Alternative splicing creates two collybistin variants, I and II. In coexpression experiments, collybistin II has been shown to induce the formation of submembraneous gephyrin aggregates which cluster with heterooligomeric glycine receptors (GlyRs). Here we identified residues critical for interaction with gephyrin in the linker region between the SH3 and the DH domains of collybistin. Respective collybistin deletion mutants failed to bind gephyrin upon coexpression in heterologous cells, in GST pulldown assays and in the yeast twohybrid system. Sitedirected mutagenesis revealed polar amino acid residues as essential determinants of gephyrin binding. Furthermore, in vitro gephyrin bound simultaneously to both collybistin and the GlyRβsubunit binding motif. Our data are consistent with collybistingephyrin interactions occuring during inhibitory postsynaptic membrane formation.

Major vault protein (MVP) is the predominant member of a large cytosolic ribonucleoprotein particle, termed vault. We have previously shown that MVP derived from electric ray electric organ becomes phosphorylated by protein kinase C in vitro and by tyrosine kinase in vivo. Here we show that MVP from two mammalian cell lines (CHO and PC12 cell) becomes highly phosphorylated by endogenous protein kinases in cellfree systems. The susceptibility to protein kinases differs substantially from those observed in MVP derived from electric organ. Phosphorylation of MVP depends on the presence of Mg2+ and can be inhibited by the chelating agent EDTA. Inhibitors of casein kinase II attenuate the phosphorylation of MVP. In contrast to CHO cells, addition of recombinant casein kinase II enhances the phosphorylation of MVP in PC12 cells. Endogenous kinase activity is of particulate nature and copurifies with vault particles. Immunoaffinity purified vaults containing recombinant tagged MVP expressed in CHO cells reveal no autophosphorylation, suggesting that protein kinase activity is not an intrinsic property of vaults. Our results suggest that cellspecific phosphorylation of MVP may play a critical role in vault function.

Prothymosin α (ProTα ) is a highly conserved and widely distributed protein whose physiological functions remain elusive. In previous work we identified high and low affinitybinding sites for ProTα in lymphoid cells. Here we demonstrate, by affinity crosslinking and affinity chromatography, the existence of three binding partners (31, 29, and 19kDa) for ProTα in the membrane of PHAactivated lymphoblasts. These surface molecules possess the expected affinity and specificity for a ProTα receptor. Examination of the expression of this complex of molecules by flow cytometry reveals that they bind ProTα in a specific and saturable way. In addition, the distribution of the receptor on the cell surface was studied by fluorescence microscopy; a caplike structure at one of the poles of the cells was identified. These results represent a new and promising approach in the research on ProTα, opening the way toward the understanding of the molecular mechanism of action of this protein.

Bradykinin released by the endothelium is thought to play an important local role in cardiovascular regulation. However, the molecular identity of endothelial proteases liberating bradykinin from its precursors remained unclear. Using RTPCR and Southern blotting techniques we detected mRNA for tissue kallikrein (KLK1) in human umbilical vein endothelial cells and in bovine aortic endothelial cells. Protein expression was confirmed by precipitation of KLK1 from lysates of endothelial cells prelabeled with [35S]cysteine/methionine. Partial purification of tissue kallikrein from total endothelial cell extracts resulted in a protein triplet of about 50 kDa in Western blots using specific antiKLK1 antibodies. The immunodetection of tissue kallikrein antigen in the fractions from ion exchange chromatography correlated with the presence of amidolytic tissue kallikrein activity. Stimulation of endothelial cells with angiotensin II (ANGII), which recently has been shown to activate the vascular kinin system and to cause vasodilation, resulted in the release of bradykinin and kallidin. ANGIIdependent relaxation of preconstricted rings from human umbilical veins was abolished in the presence of a specific tissue kallikrein inhibitor. We conclude that endothelial cells de novo express significant amounts of tissue kallikrein, which likely serves in the local generation of vasoactive kinins.

In monolayer cultures human rheumatoid synovial fibroblasts (HRSF) secrete gelatinase A (MMP-2) and, unlike other human fibroblasts, to a minor extent also gelatinase B (MMP-9) as inactive proenzymes. In this regard HRSF resemble the fibrosarcoma cell line HT-1080. Unlike HT-1080, however, HRSF do not increase the secretion of MMP-9 in response to phorbol-12-myristate-13-acetate. This indicates that in HRSF the protein kinase C pathway for an enhanced MMP-9 secretion is inactive. None of the substances used in our study increased MMP-9 secretion, but some of them inhibited MMP-9 secretion. The secretion of MMP-2 could not be enhanced either, not even by dbcAMP, which has been reported to be effective in Sertoli and peritubular cells. Activation of MMP-2 in HRSF could be induced by treatment with concanavalin A (ConA) or cytochalasin D, as was shown for other cell types. This activation was not accompanied by a significant change in the amount of secreted TIMP-1 and TIMP-2. In contrast to reports on human skin fibroblasts, however, the activation of MMP-2 could not be induced in HRSF by treatment of the cells with monensin or sodium orthovanadate. Moreover, monensin was shown to act as an inhibitor of ConA or cytochalasin Dmediated activation. Additionally, and in contrast to a report on a rat fibroblast cell line, MMP-2 activation is not mediated via the MAP kinase pathway in HRSF: PD 98059, a specific inhibitor of MAP kinase kinase, did not inhibit the activation of MMP-2. Similarly ineffective were PD 169316, an inhibitor for p38 MAP kinase, other inhibitors for protein kinases as lavendustin A, Gö 6983, wortmannin, rapamycin, as well as the protein tyrosine kinase inhibitors herbimycin A and genistein. Only staurosporin, a broad spectrum inhibitor of protein kinases, and the ionophores monensin and A 23187 effectively inhibited MMP-2 activation in HRSF. Our results demonstrate that MMP-2 can be activated by quite different pathways, and that different cells, even when belonging to the fibroblast family, do not necessarily use the same activating pathways.

Two ferredoxin genes, fdA and fdB, from the extremely thermoacidophilic crenarchaeon Acidianus ambivalens have been sequenced; the sequences share 86% similarity. Whereas the deduced protein sequence of the ferredoxin FdA clearly contains a zincbinding motif, the corresponding sequence of the FdB is devoid of this motif. Thus far, only the zinccontaining ferredoxin, FdA, from A. ambivalens has been chemically and functionally characterized from its native source. Using RTPCR and Northern blot analysis, we show that both ferredoxins are expressed by A. ambivalens under either anaerobic or aerobic growth conditions. The zincfree ferredoxin, FdB, was overexpressed in E. coli and purified to homogeneity. Using EPR spectroscopy, we could demonstrate that FdB contains one [3Fe-4S]1+/0 and one [4Fe-4S]2+/1+ cluster. The reduction potential of the [3Fe-4S]1+/0 cluster was determined as 235±10 mV, at pH 6.5, by EPRmonitored redox titration. The high melting temperature of 108±2 C of FdB determined by CD spectroscopy reveals that it is not the binding of the Zn2+ that induces the extreme thermostability of these ferredoxins.

A serine endopeptidase with a molecular mass of 25 kDa has been purified from the culture filtrate of Trichoderma viride to electrophoretic homogeneity. The isoelectric point was determined at 7.3. Two carboxyl sites at Arg22 and Lys29 of the oxidized insulin Bchain were cleaved, and peptidylpnitroanilide substrates with Lys or Arg at the P1 position were also hydrolyzed by the enzyme. These results suggest that the specificity of T. viride protease is similar to that of trypsin. However, the hydrolytic activity toward casein of T. viride protease was less than that of porcine trypsin. The aminoterminal sequence of the enzyme protein is similar to that of bovine trypsin. It seems that the trypsin of T. viride is a protease which is promising for the substitution of animal trypsin in the food industry and in medicine at this stage.

Human Tear Lipocalin/von Ebners gland protein (TL) is a member of the lipocalin superfamily. The protein is secreted by a number of serous glands and tissues and is overproduced under conditions of stress, infection and inflammation. In addition to its typical affinity for lipophilic ligands it was recently found to be able to inhibit cysteine proteinases [vant Hof et al., J. Biol. Chem. 272 (1997), 18371841], probably due to the presence of amino acid motifs resembling the papain binding domains of family 2 cystatins. In this work we have used a recombinant protein to confirm the results obtained with native TL. The inhibitory activity of the recombinant protein against papain was dependent on the ratio of papain and TL. At higher papain concentrations, the Nterminal sequence of TL was cleaved off by the protease, indicating that it can act in an inhibitor or a substratelike mode. This behaviour resembles that observed with certain chicken cystatin mutants. Using a recombinant TL mutant we found that the two Leu residues (Leu4-Leu5) contained within the first cystatinlike motif are absolutely essential for the inhibitory activity. These results were supported by experiments using a recombinant form of the corresponding pig von Ebners gland protein (VEGp). This protein, which does not possess a fully conserved first cystatinlike motif, is unable to inhibit papain.