p27 is involved in N-cadherin-mediated contact inhibition of cell growth and S-phase entry.
In this study the direct involvement of cadherins in adhesion-mediated growth inhibition was investigated. It is shown here that overexpression of N-cadherin in CHO cells significantly suppresses their growth rate. Interaction of these cells and two additional fibroblastic lines with synthetic beads coated with N-cadherin ligands (recombinant N-cadherin ectodomain or specific antibodies) leads to growth arrest at the G1 phase of the cell cycle. The cadherin-reactive beads inhibit the entry into S phase and the reduction in the levels of cyclin-dependent kinase (cdk) inhibitors p21 and p27, following serum-stimulation of starved cells. In exponentially growing cells these beads induce G1 arrest accompanied by elevation in p27 only. We propose that cadherin-mediated signaling is involved in contact inhibition of growth by inducing cell cycle arrest at the G1 phase and elevation of p27 levels. (+info)
Phosphorylation of the DNA repair protein APE/REF-1 by CKII affects redox regulation of AP-1.
The DNA repair protein apurinic endonuclease (APE/Ref-1) exerts several physiological functions such as cleavage of apurinic/apyrimidinic sites and redox regulation of the transcription factor AP-1, whose activation is part of the cellular response to DNA damaging treatments. Here we demonstrate that APE/Ref-1 is phosphorylated by casein kinase II (CKII). This was shown for both the recombinant APE/Ref-1 protein (Km=0.55 mM) and for APE/Ref-1 expressed in COS cells. Phosphorylation of APE/Ref-1 did not alter the repair activity of the enzyme, whereas it stimulated its redox capability towards AP-1, thus promoting DNA binding activity of AP-1. Inhibition of CKII mediated phosphorylation of APE/Ref-1 blocked mutagen-stimulated increase in AP-1 binding. It also abrogated the induction of c-Jun protein and rendered cells more sensitive to induced DNA damage. Thus, phosphorylation of APE/Ref-1 appears to be involved in regulating the different physiological activities of the enzyme. CKII mediated phosphorylation of APE/Ref-1 and concomitant increase in AP-1 binding activity appears to be a novel mechanism of cellular stress response, forcing transcription of AP-1 target gene(s) the product(s) of which may exert protective function. (+info)
Reversal of hyperlipidaemia in apolipoprotein C1 transgenic mice by adenovirus-mediated gene delivery of the low-density-lipoprotein receptor, but not by the very-low-density-lipoprotein receptor.
We have shown previously that human apolipoprotein (apo)C1 transgenic mice exhibit hyperlipidaemia, due primarily to an impaired clearance of very-low-density lipoprotein (VLDL) particles from the circulation. In the absence of at least the low-density-lipoprotein receptor (LDLR), it was shown that APOC1 overexpression in transgenic mice inhibited the hepatic uptake of VLDL via the LDLR-related protein. In the present study, we have now examined the effect of apoC1 on the binding of lipoproteins to both the VLDL receptor (VLDLR) and the LDLR. The binding specificity of the VLDLR and LDLR for apoC1-enriched lipoprotein particles was examined in vivo through adenovirus-mediated gene transfer of the VLDLR and the LDLR [giving rise to adenovirus-containing (Ad)-VLDLR and Ad-LDLR respectively] in APOC1 transgenic mice, LDLR-deficient (LDLR-/-) mice and wild-type mice. Remarkably, Ad-VLDLR treatment did not reduce hyperlipidaemia in transgenic mice overexpressing human APOC1, irrespective of both the level of transgenic expression and the presence of the LDLR, whereas Ad-VLDLR treatment did reverse hyperlipidaemia in LDLR-/- and wild-type mice. On the other hand, Ad-LDLR treatment strongly decreased plasma lipid levels in these APOC1 transgenic mice. These results suggest that apoC1 inhibits the clearance of lipoprotein particles via the VLDLR, but not via the LDLR. This hypothesis is corroborated by in vitro binding studies. Chinese hamster ovary (CHO) cells expressing the VLDLR (CHO-VLDLR) or LDLR (CHO-LDLR) bound less APOC1 transgenic VLDL than wild-type VLDL. Intriguingly, however, enrichment with apoE enhanced dose-dependently the binding of wild-type VLDL to CHO-VLDLR cells (up to 5-fold), whereas apoE did not enhance the binding of APOC1 transgenic VLDL to these cells. In contrast, for binding to CHO-LDLR cells, both wild-type and APOC1 transgenic VLDL were stimulated upon enrichment with apoE. From these studies, we conclude that apoC1 specifically inhibits the apoE-mediated binding of triacylglycerol-rich lipoprotein particles to the VLDLR, whereas apoC1-enriched lipoproteins can still bind to the LDLR. The variability in specificity of these lipoprotein receptors for apoC1-containing lipoprotein particles provides further evidence for a regulatory role of apoC1 in the delivery of lipoprotein constituents to different tissues on which these receptors are located. (+info)
Proteoglycan involvement in polyamine uptake.
We have evaluated the possible role of proteoglycans in the uptake of spermine by human lung fibroblasts. Exogenous glycosaminoglycans behaved as competitive inhibitors of spermine uptake, the most efficient being heparan sulphate (Ki=0.16+/-0.04 microM). Treatment of fibroblasts with either heparan sulphate lyase, p-nitrophenyl-O-beta-D-xylopyranoside or chlorate reduced spermine uptake considerably, whereas chondroitin sulphate lyase had a limited effect. Inhibition of polyamine biosynthesis with alpha-difluoromethylornithine resulted in an increase of cell-associated heparan sulphate proteoglycans exhibiting higher affinity for spermine. The data indicate a specific role for heparan sulphate proteoglycans in the uptake of spermine by fibroblasts. Spermine uptake by pgsD-677, a mutant Chinese hamster ovary cell defective in heparan sulphate biosynthesis, was only moderately reduced (20%) compared with wild-type cells. Treatment of mutant cells with the above-mentioned xyloside resulted in a greater reduction of endogenous proteoglycan production as well as a higher inhibition of spermine uptake than in wild-type cells. Moreover, treatment with chondroitin sulphate lyase resulted in a selective inhibition of uptake in mutant cells, indicating a role for chondroitin/dermatan sulphate proteoglycans in the uptake of spermine by these cells. Fibroblasts, made growth-dependent on exogenous spermine by alpha-difluoromethylornithine treatment, were growth-inhibited by heparan sulphate or beta-D-xyloside, which might have future therapeutical implications. (+info)
Non-serum-dependent chemotactic factors produced by Candida albicans stimulate chemotaxis by binding to the formyl peptide receptor on neutrophils and to an unknown receptor on macrophages.
Serum-free culture filtrates of six Candida species and Saccharomyces cerevisiae were found to contain chemoattractants for human polymorphonuclear leukocytes (PMNs) and a mouse macrophage-like cell line, J774. The chemotactic factors differed for the PMN and J774 cells, however, in terms of heat stability, kinetics of liberation by the yeast cells, and divalent cation requirements for production. The chemoattractant in Candida albicans culture filtrates appeared to act through the formyl peptide receptor (FPR) of PMNs, since it was found to induce chemotaxis of Chinese hamster ovary (CHO) cells that were expressing the human FPR but did not induce chemotaxis of wild-type CHO cells. The C. albicans culture filtrates also induced migration of PMNs across confluent monolayers of a human gastrointestinal epithelial cell line, T84; migration occurred in the basolateral-to-apical direction but not the reverse direction, unless the epithelial tight junctions were disrupted. J774 cells did not migrate toward the formylated peptide (fMet-Leu-Phe; fMLF), and chemotaxis toward the C. albicans culture filtrate was not inhibited by an FPR antagonist (t-butoxycarbonyl-Met-Leu-Phe), suggesting that a different receptor mediated J774 cell chemotaxis. In conclusion, we have identified a receptor by which a non-serum-dependent chemotactic factor (NSCF) produced by C. albicans induced chemotaxis of PMNs. Additionally, we have shown that NSCF was active across epithelial monolayers. These findings suggest that NSCFs produced by C. albicans and other yeast species may influence host-pathogen interactions at the gastrointestinal tract mucosal surface by inducing phagocytic-cell infiltration. (+info)
Enhanced Th1 and dampened Th2 responses synergize to inhibit acute granulomatous and fibrotic responses in murine schistosomiasis mansoni.
In murine schistosomiasis mansoni, CD4(+) Th1 and Th2 cells participate in the ovum-induced granulomatous inflammation. Previous studies showed that the interleukin-12 (IL-12)-induced Th1 response strongly suppressed the Th2-cell-mediated pulmonary granuloma development in naive or primed mice. However, liver granulomas were only moderately suppressed in egg-vaccinated, recombinant IL-12 (rIL-12)-treated infected mice. The present study shows that repeated rIL-12 injections given during early granuloma development at 5 to 7 weeks after infection prolonged the Th1 phase and resulted in gamma interferon-mediated suppression of liver granulomas. The timing is crucial: if given at 6 to 8 weeks, during the Th2-dominated phase of florid granuloma growth, the treatment is ineffective. Daily injections of rIL-12 given between 5 and 7.5 weeks during the period of granuloma growth achieved a somewhat-stronger diminution in granuloma growth with less deposition of collagen but caused 60% mortality and liver pathology. In contrast, combined treatment with rIL-12 and anti-IL-4-anti-IL-10 monoclonal antibody (MAb) injections given during the Th2 phase strongly inhibited liver granuloma growth without mortality. The diminished inflammatory response was accompanied by less deposition of collagen in the liver. Moreover, neutralization of endogenous IL-12 by anti-IL-12 MAbs effectively decreased the early Th1 phase (between 5 and 6 weeks after infection) but not the developing Th2 phase (5 to 7 weeks) of granuloma development. These studies indicate that the granulomatous response in infected mice can be manipulated by utilizing the Th1-Th2-subset antagonism with potential salutary results in the amelioration of fibrous pathology. (+info)
Identification of a cytolethal distending toxin gene locus and features of a virulence-associated region in Actinobacillus actinomycetemcomitans.
A genetic locus for a cytolethal distending toxin (CDT) was identified in a polymorphic region of the chromosome of Actinobacillus actinomycetemcomitans, a predominant oral pathogen. The locus was comprised of three open reading frames (ORFs) that had significant amino acid sequence similarity and more than 90% sequence identity to the cdtABC genes of some pathogenic Escherichia coli strains and Haemophilus ducreyi, respectively. Sonic extracts from recombinant E. coli, containing the A. actinomycetemcomitans ORFs, caused the distension and killing of Chinese hamster ovary cells characteristic of a CDT. Monoclonal antibodies made reactive with the CdtA, CdtB, and CdtC proteins of H. ducreyi recognized the corresponding gene products from the recombinant strain. CDT-like activities were no longer expressed by the recombinant strain when an OmegaKan-2 interposon was inserted into the cdtA and cdtB genes. Expression of the CDT-like activities in A. actinomycetemcomitans was strain specific. Naturally occurring expression-negative strains had large deletions within the region of the cdt locus. The cdtABC genes were flanked by an ORF (virulence plasmid protein), a partial ORF (integrase), and DNA sequences (bacteriophage integration site) characteristic of virulence-associated regions. These results provide evidence for a functional CDT in a human oral pathogen. (+info)
Pseudomonas aeruginosa exoenzyme S is a biglutamic acid ADP-ribosyltransferase.
Kinetic analysis of two mutations within Pseudomonas aeruginosa exoenzyme S (ExoS) showed that a E379D mutation inhibited expression of ADP-ribosyltransferase activity but had little effect on the expression of NAD glycohydrolase activity while a E381D mutation inhibited expression of both activities. These data identify ExoS as a biglutamic acid ADP-ribosyltransferase, where E381 is the catalytic residue and E379 contributes to the transfer of ADP-ribose to the target protein. (+info)