Biomedical subjects

D Kletsas

Publications and source records attributed to D Kletsas.

34 records · Page 2Linked to original sources

PubMed1999

The therapeutic potential of targeting drugs at transcription factors.

The pivotal role of gene transcription in a plethora of biological processes indicates that transcription represents a suitable target for potential therapeutic intervention. Ultimately, the pathophysiology of numerous human disease processes must be understood in terms of changes in gene expression within relevant body cell types. There is mounting evidence that genetic variation in transcription factors and/or their binding-site sequences, as well as environmentally induced malfunctioning of these proteins, contribute to common multifactorial disorders including cancer, diabetes, ischaemic heart disease and neural disorders. Even in 'non-inheritable' infectious diseases, alterations of host-cell transcriptional regulation play an important role in pathogenesis. The enormous progress in understanding the mechanisms of transcriptional control offers hope for the development of a new generation of drugs. Such compounds could be specifically designed to modulate either the synthesis of transcription factors, the regulation of their activity by small-molecule bioligands or phosphorylation events, their interactions with activator/repressor proteins or their binding to DNA. Given the remarkable specificity of this approach, it is anticipated that these agents will provide superior tools for the prevention and treatment of a diverse panel of clinical disorders in the not too distant future.

Journal Article↗

PubMed1998

Mechanical stress induces DNA synthesis in PDL fibroblasts by a mechanism unrelated to autocrine growth factor action.

Periodontal regeneration is thought to require the proliferation of stress-sensitive periodontal ligament (PDL) fibroblast cells. The influence of physiological amounts of mechanical stretching on the DNA synthesis potential of human PDL fibroblasts was examined by means of an established, simple in vitro system of stretch application. A significant increase in the relative levels of incorporation of tritiated thymidine was observed in cultures stretched for 1-6 h. Neutralising antibodies for platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) did not blunt the DNA synthesis induction. This mitogenic response to stretch appears to be independent of an autocrine mechanism involving growth factors in general, because stretch-conditioned medium, when transferred to non-stretched fibroblasts, did not mimic the mitogenic effect of stretch.

Culture Media, Conditioned↗

PubMed1998

The CRH-ACTH-biogenic amine axis in invertebrate immunocytes activated by PDGF and TGF-beta.

In immunocytes from the mollusc Mytilus galloprovincialis, the major pathway followed by platelet-derived growth factor (PDGF)-AB and transforming growth factor (TGF)-beta1 in provoking the release of norepinephrine, epinephrine and dopamine into cell-free hemolymph (serum) is mediated by a corticotropin-releasing hormone-adrenocorticotropin hormone (CRH-ACTH) biogenic amine axis. This axis not only annulled the inhibiting properties of PDGF-AB, it even reversed the latter's effect, while the inducing effect of TGF-beta1 was amplified. These findings show that non-classical immune-neuroendocrine molecules, such as PDGF-AB and TGF-beta1, are involved in building stress response, using the same conserved mechanisms present from invertebrates to vertebrates.

Adrenocorticotropic Hormone↗

PubMed1998

Neutral endopeptidase-24.11 (NEP) activity in human fibroblasts during development and ageing.

Neutral endopeptidase-24.11 (NEP, EC 3.4.24.11) is a cell surface Zn metallopeptidase that hydrolyzes bioactive regulatory peptides. Using a spectrofluorimetric procedure, we assessed NEP activity in plasma membranes of normal human skin and lung fibroblasts. We found a considerable increase in NEP activity during fetal-to-adult transition. Adult skin fibroblasts from an old donor exhibited significantly higher levels of NEP activity than cells from young donors. Interestingly, however, the NEP activity of fibroblasts from a centenarian donor was similar to that of cells from young donors. Increased levels of NEP activity were also found in in vitro aged lung fibroblasts. Finally, adrenocorticotropin hormone (ACTH (1-24)), a regulatory peptide that can be cleaved by NEP, provoked an increase in enzymic activity in fetal and young adult donor fibroblasts and a decrease in this activity in fibroblasts from adult and old donors. This finding suggests that ageing may affect NEP activity.

Adult↗

PubMed1998

The highly reducing sugar 2-deoxy-D-ribose induces apoptosis in human fibroblasts by reduced glutathione depletion and cytoskeletal disruption.

2-deoxy-D-Ribose (dRib), the most reducing sugar, induces apoptosis in normal human fibroblasts, as judged by cytoplasmic shrinkage, chromatin condensation, DNA fragmentation and mitochondrial depolarization. This effect is independent from culture conditions, such as cell density and the presence or absence of serum in the culture milieu, suggesting that dRib-induced apoptosis is cell cycle-independent. dRib was found also to provoke disruption of the actin filament network and detachment from the substratum, while at the same time, interestingly, it increases the expression of several integrins and cell adhesion molecules. Furthermore, dRib was found to reduce the intracellular levels of reduced glutathione (GSH). The apoptotic process was not affected by the macromolecular-synthesis inhibitors cycloheximide and actinomycin D. On the contrary, the antioxidant N-acetyl-L-cysteine (NAC) fully blocks the dRib-induced apoptosis by preventing GSH depletion, while it also inhibits actin-filament-network disruption and mitochondrial depolarization. The above indicate that dRib induces apoptosis in human fibroblasts by a mechanism involving glutathione metabolism and oxidative stress, as well as disturbance of cytoskeletal integrity and cell adhesion.

Acetylcysteine↗

PubMed1998

PDGF and TGF-beta induce cell shape changes in invertebrate immunocytes via specific cell surface receptors.

The presence of PDGF receptor-alpha- and -beta- and TGF-beta-receptor (type II)-like molecules on the plasma membranes of the immunocytes of the mollusc Mytilus galloprovincialis was demonstrated by an immunocytochemical procedure. Furthermore, the present study provides evidence that PDGF-AB and TGF-beta1 provoke cell shape changes in immunocytes via interactions with the respective receptors and that these extracellular signals are transduced along the phosphoinositide signaling pathway.

Animals↗

PubMed1998

Interactions of signaling pathways in ACTH (1-24)-induced cell shape changes in invertebrate immunocytes.

ACTH (1-24) induces cell shape changes in the immunocytes of the bivalve mollusc, Mytilus galloprovincialis. Using computer-assisted microscopic image analysis, we have found that the G protein antagonist suramin sodium, the adenylate cyclase inhibitor 2',5'-dideoxyadenosine, and the protein kinase inhibitor staurosporine inhibit this effect. The highly specific inhibitors H-89 (for protein kinase A) and calphostin C (for protein kinase C) only inhibited partially the morphological alterations. In contrast, the simultaneous action of H-89 and calphostin C completely blocked these changes. The above findings indicate that ACTH (1-24) induces cell shape changes in molluscan immunocytes via adenylate cyclase/cAMP/protein kinase A pathway, as well as the activation of protein kinase C.

Adenylyl Cyclase Inhibitors↗

PubMed1997

Autocrine growth regulation in fetal and adult human fibroblasts.

Medium conditioned (CM) by human fetal fibroblasts stimulates proliferation in sparse cultures. This effect is inhibited by suramin and staurosporine, indicating the presence of autocrine growth factors in CM. On the contrary, CM inhibits DNA synthesis in confluent cultures, suggesting a regulatory role for the secreted factors. The growth regulatory profile of CM persists during in vitro ageing. However, it changes dramatically during the fetal-to-adult transition, as adult human fibroblasts are stimulated by CM, regardless of the culture density. These effects are similar to those that TGF-beta is known to have on fetal and adult human fibroblasts. Indeed TGF-beta is present in media conditioned by human fibroblasts, but CM-activity cannot be ascribed solely to this factor. Fibroblasts originating from different tissues exhibit the same autocrine regulatory features, suggesting the general character of this mechanism.

Adult↗

PubMed1997

Effect of PDGF and TGF-beta on the release of biogenic amines from invertebrate immunocytes and their possible role in the stress response.

PDGF-AB and TGF-beta 1 intervene in molluscan stress response, the former inhibiting and the latter inducing the release of norepinephrine and epinephrine from hemocytes. These amines are down-regulated even when TGF-beta 1 is added to hemolymph pre-incubated with PDGF-AB. The opposite behaviour is observed if the growth factors are reversed. The dopamine response is not affected in either case, even after the addition of CRH or ACTH. After pre-incubation with PDGF-AB or TGF-beta 1 in the presence of CRH or ACTH, norepinephrine and epinephrine release falls. These findings suggest that when the interaction is between growth factors, the order of combination is crucial, while in cases where the interaction is between growth factors and other peptides, such as CRH and ACTH, the order is of no importance.

Adrenocorticotropic Hormone↗

PubMed1997

PDGF- and TGF-beta-induced changes in cell shape of invertebrate immunocytes: effect of calcium entry blockers.

The cellular activity of hemocytes from the marine mollusc Mytilus galloprovincialis was studied using computer-assisted microscopic image analysis. PDGF-AB and TGF-beta 1 caused changes in cellular shape and induced the immunocytes to migrate in a chemotactic manner. The effect of PDGF-AB was more potent than that of TGF-beta 1, and the responses were dose-correlated for PDGF-AB, while they were dose-dependent up to 5 pg/ml for TGF-beta 1. Moreover, the PDGF-AB response was extracellular Ca(2+)-independent, while TGF-beta 1 was Ca(2+)-dependent.

Animals↗

PubMed1996

Immunocytochemical evidence of PDGF- and TGF-beta-like molecules in invertebrate and vertebrate immunocytes: an evolutionary approach.

Immunoreactive platelet-derived growth factor-AB and transforming growth factor-beta 1 were demonstrated in invertebrate and vertebrate immunocytes by an immunocytochemical procedure. These factors are only present in phagocytic cells among invertebrate immunocytes, whereas in vertebrate immunocytes they are found in monocytes, granulocytes, lymphocytes, thrombocytes and platelets. These results, in agreement with previous reports, represent further evidence in favour of the hypothesis that Nature has followed a conservative strategy in using a common pool of signal molecules that have been highly conserved throughout evolution.

Animals↗

PubMed1995

The growth-inhibitory block of TGF-beta is located close to the G1/S border in the cell cycle.

Transforming growth factor-beta (TGF-beta) inhibits DNA synthesis in dense cultures of young human embryonic fibroblasts and antagonizes the mitogenic action of platelet-derived growth factor (PDGF). The inhibition of the PDGF-BB action by TGF-beta was independent of the induction of mRNAs for the PDGF-A chain and PDGF-beta receptor, the predominant types of PDGF receptor in human fibroblasts. The TGF-beta-mediated inhibition did not influence the expression of various genes that are involved in the transition from the arrested (GO) state to the S phase of the cell cycle. Indeed, TGF-beta upregulated the "early" genes c-myc, c-fos, and junB and downregulated the growth arrest-specific (gas) genes. These results suggest that the inhibition of DNA synthesis by TGF-beta in human fibroblasts is independent of modulation of expression of early and gas genes, placing the TGF-beta block comparatively late in the GO to S transition. In cultures of senescent human fibroblasts TGF-beta stimulated DNA synthesis but, nevertheless, had the same effect as in young cells on the expression of PDGF chains and receptor genes, as well as on early and gas genes, with the exception of a significantly lower induction of c-fos.

Cell Cycle Proteins↗

PubMed1994

Restoration of down-regulated PDGF receptors by TGF-beta in human embryonic fibroblasts. Enhanced response during cellular in vitro aging.

The study of [125I]PDGF-BB binding to normal human embryonic lung fibroblasts, quiescent when cultured at sparsity in the presence of minute concentrations of homologous PDS, reveals approximately 2 x 10(5) binding sites for PDGF per cell; this number significantly increases during prolonged quiescence of the culture. As late as 48 h after down-regulation of PDGF receptors, the cells restore only partially their capacity to bind PDGF, with aged cells (above CPD 45) responding more rapidly and efficiently than younger ones. TGF-beta significantly enhances restoration of PDGF receptors and, in aged cells in particular, its presence results in total receptor recovery within 24 h, suggesting a concerted action of PDGF and TGF-beta regulating the proliferation of human fibroblasts in tissue regeneration.

Cells, Cultured↗

PubMed1993

Stimulation of human embryonic lung fibroblasts by TGF-beta and PDGF acting in synergism. The role of cell density.

The concerted action of TGF-beta and PDGF on a diploid human embryonic lung fibroblast cell strain (Flow 2002) grown in an homologous environment is investigated here. In sparse cultures, TGF-beta stimulates DNA synthesis over a broad concentration range (0.1-10 ng/ml). Furthermore, it acts in synergism with PDGF, a phenomenon which persists also during in vitro aging of the cells. Preincubation of TGF-beta with the fibroblasts up to 12 hours reduces the subsequent PDGF binding to the cells, while prolonged preincubation restores PDGF binding to control levels. Finally, in cultures of higher cell densities, TGF-beta ceases to stimulate DNA synthesis, whereas PDGF continues even at cell confluency, retains its stimulatory activity suggesting different roles for the two growth factors during the wound healing process.

Aging↗

PubMed1992

Quiescence and proliferative response of normal human embryonic fibroblasts in homologous environment. Effect of aging.

A cell culture system for the study of human serum growth factors is described. It is based on a diploid human embryonic lung fibroblast cell strain (Flow 2002) with a finite life span (60 +/- 3 CPDs). When maintained in homologous (human) plasma-derived serum (PDS) at concentrations as low as 0.05%, the cells attain quiescence. Under these conditions, they remain viable for at least 14 days and they readily respond when stimulated to proliferate by human serum or human PDS, as well as by growth factors, such as PDGF, EGF, FGF. During in vitro aging, the cells retain their responsiveness to these growth stimuli, although the net proliferative effect decreases as they approach senescence.

Blood↗

PubMedDate not supplied

STI571 as a potent inhibitor of growth and invasiveness of human epithelial breast cancer cells.

STI571, a specific tyrosine kinase inhibitor, exhibits a substantial therapeutic activity in patients with chronic myeloid leukaemia and gastrointestinal stromal tumors. In this study we examined the activity of STI571 on the growth and invasiveness of three human epithelial breast cancer cell lines of low (MCF-7) and high (ZR-75-1 and MDA-MB-231) invasive potential. Growth of all cell lines in serum-containing medium was significantly inhibited by STI571 in a dose-dependent manner, with an average IC50 of approximately 5-6 microM. Flow cytometric analysis revealed that this effect is characterized by an accumulation of all breast cancer cell types tested in the G2/M-phase of the cell cycle with a concomitant decrease of the percentage of cells in the S-phase. Interestingly, no increase in apoptosis was observed, indicating that the effect of this kinase inhibitor is cytostatic rather than cytotoxic. In addition, STI571 exerts a significant inhibition effect on the invasion of the highly invasive breast cancer cell lines ZR-75-1 and MDA-MB-231. These results encourage further preclinical investigations on the mechanisms underlying the inhibitory effects of STI571, which may be of great value in breast cancer treatment.

Adenocarcinoma↗