DNA Synthesis In Human Fibroblasts Research Articles

Activation of Ras signaling pathways by pyrroloquinoline quinone in NIH3T3 mouse fibroblasts

Pyrroloquinoline quinone (PQQ) has been implicated in certain physiological activities in mammals such as functioning as a potent growth factor in mice, and promoting DNA synthesis in human fibroblasts. These are clearly important physiological functions, however, the molecular mechanisms involved in PQQ activity are not yet fully understood. In order to address this, in this study we analyzed the effects of PQQ on the proliferation of NIH3T3 mouse fibroblasts and on their intracellular signal transduction mechanism. When activated c-Ha-ras-transformed NIH3T3 cells were treated with PQQ in the presence of 0.5% calf serum in DMEM, the cells showed significantly increased viability. After PQQ addition, flow cytometric analysis revealed a decrease in the population of cells in the G0/G1 phase and a concomitant increase in cells in the S and G2/M phases. Although treatment with SNAP, an NO donor, reduced cell viability, this effect was abolished by the addition of PQQ. Activation of ERK and PKC-epsilon was detected immediately after the addition of PQQ, and subsequent increases in the phosphorylation of Rb and c-Jun were observed. On the other hand, protein expression levels of growth-inhibitory molecules such as IkappaB and p27 decreased after PQQ treatment. These results suggest that PQQ stimulates cell proliferation through NO-sensitive Ras-mediated signaling pathways.

Activation of β3 Adrenergic Receptor Decreases DNA synthesis in Human Skin Fibroblasts Via Cyclic GMP/Nitric Oxide Pathway

Background: Evidences have shown that β₁ and β₂ adrenoceptors co-exist in human fibroblasts, but it is not yet clear the functional expression of β₃ adrenoceptor in these cells. The aim of this study was to investigate the expression and biological effect of β₃ adrenoceptor activation in human skin fibroblast and the different signaling pathways involved in its effect. Methods: For this purpose in vitro cultures of human skin fibroblast were established from human foreskin and grown in Dulbecco’s modified Eagle’s medium. The effect of ZD 7114 (β₃ agonist) on cell DNA synthesis, radioligand binding assay, cyclic GMP and cyclic AMP accumulation and nitric oxide synthase (NOS) activity were evaluated. Results: ³H-CGP binding to human fibroblast membranes was a saturable process to a single class of binding site. The equilibrium parameters were: Kd 20±3 pM and Bmax 222±19 fmol/mg protein. Ki values showed that these cells express a high number of β₃adrenoceptor subtypes. ZD 7114 stimulation of β₃ adrenoceptor exerts a concentration-dependent inhibition of DNA synthesis and cAMP accumulation with parallel increase in NOS activity that led to cGMP accumulation. All these effects were blocked by the β₃ adrenoceptor antagonist (SR 59230A). The effect of ZD 7114 on DNA synthesis significantly correlated with its action either on cAMP or NOS-cGMP signaling system. Inhibitors of NOS activity and NO-sensitive guanylate cyclase prevented the inhibitory effect of ZD 7114 on DNA synthesis. In addition, the β₃ adrenoceptor-dependent increase in cGMP and activation of NOS were blocked by the inhibition of phospholipase C (PLC), calcium/calmodulin (CaM), endothelial NOS activity and cGMP accumulation. Conclusions: β₃ adrenoceptor activation exerts inhibitory effect on human fibroblast DNA synthesis as a result of the activation of NO-cGMP pathway and the inhibition of adenylate cyclase activity. The mechanism appears to occurs secondarily to stimulation of PLC and CaM. This in turn triggers cascade reaction leading to increase production of NO-cGMP with decrease in cAMP accumulation.

Mouse insulin-like growth factor binding protein-6: expression, purification, characterization and histochemical localization

The mitogenic and metabolic activities of insulin-like growth factors (IGF) are modulated by a family of six high affinity IGF binding proteins (IGFBPs). This study describes the expression of the mouse IGFBP-6 which is unique among IGFBPs in its preferential binding of IGF II, in insect cells using the baculovirus system. The purified, O-glycosylated IGFBP-6 was functional as shown by IGF binding and by inhibition of IGF II-stimulated DNA synthesis in human fibroblasts. Specific antibodies generated in chicken against the recombinant IGFBP-6 were used for Western blotting analysis and immunohistochemistry. Strong immunoreactivity was found in ossifying bones of the cranial base, in cell clusters of the pancreas anlage, in the trigeminal ganglion, on myoblasts, on motoneurons of the spinal cord of embryonic mice. In tissues of adult mouse, strong IGFBP-6 immunostaining was present in epidermal and peridermal layers of the skin, in meningeal layers, in long-striated skeletal muscle, and in the Langerhans’ islets of the pancreas. No immunopositive staining was observed in lung and liver indicating that sites of synthesis and IGFBP action are different.

Identification of a cyclic peptide inhibitor of platelet-derived growth factor–BB receptor-binding and mitogen-induced DNA synthesis in human fibroblasts

Peptides corresponding to residues from Loops I and III of platelet-derived growth factor–BB (PDGF-BB) were examined for their potential to act as PDGF antagonists. We have identified two peptides which directly stimulated DNA synthesis in human dermal fibroblasts and a cyclic peptide which inhibited PDGF-induced DNA synthesis. The inhibitory action of cyclic PDGF-BB 73-81, on DNA synthesis was shown to be restricted to cells which express PDGF receptors. Also cyclic PDGF-BB 73-81 specifically competed for 125I-labelled PDGF-BB but not for 125I-labelled EGF binding to their respective cellular receptors. The cyclic peptide therefore provides a minimum structure to investigate PDGF/receptor interactions and our findings confirm the importance of the loop configuration of PDGF-BB 73-81 in the native molecule. The cyclic peptide may constitute a basis for developing more potent inhibitors of PDGF action.

Inhibition of DNA Synthesis and G 1 /S-Phase Transition in Normal Human Fibroblasts Elicited by a Heat-Labile Trans-Acting Factor in Gamma-Irradiated HeLa Cell Extracts

Proliferating human cells exposed to ionizing radiation show complex cellular responses including a delay in progression through various phases in the cell cycle. These cell cycle checkpoints are regulated by mitogenic signaling pathways which transduce the extracellular signals to the cell cycle control machinery. In this study we demonstrate that microinjection of a cellular extract, prepared from gamma-irradiated (40 Gy) HeLa cells, into the cytoplasm of normal human fibroblasts results in suppression of DNA replicative synthesis, indicating the presence of a trans-acting DNA synthesis-inhibiting factor(s). The addition of this same extract to the culture medium for a short time (< or = 2 h) also inhibits DNA synthesis in human fibroblasts, affecting both replicon initiation and DNA chain elongation processes. Moreover, a 2-h incubation of the fibroblast cultures with the extract causes a transient delay in cell progression from G1 to S phase coupled with up-regulation of the p53 tumor suppressor protein. Both the DNA synthesis-inhibiting and G1-phase-blocking activities are reduced markedly when the extract is heated (80 degrees C; 10 min) prior to its addition to the culture medium. On the other hand, pretreatment of the fibroblast cultures with KN62, an inhibitor of calmodulin-dependent kinase II (CaMKII), serves to abrogate the inhibitory effect of the extract on DNA synthesis without influencing its ability to induce the G1-phase block. These results are compatible with the presence in HeLa cell extracts of a heat-labile trans-acting factor that triggers, in normal human cells, the activation of (1) a CaMKII-dependent signal transduction pathway mediating suppression of DNA synthesis and (2) a p53-dependent pathway mediating G1-phase checkpoint control.

Correlation of the lipophilicity of xenobiotics with their synergistic effects on dna synthesis in human fibroblasts

The binary combination effects on DNA synthesis of human fibroblasts were investigated using 2,4-D with 15 xenobiotics of different chemical substance classes. Results were compared with previous investigations on cell growth. Each of the 15 chemicals tested at their no effect concentrations (NOEC's) increased the effects of 2,4-D on DNA synthesis. Thereby, the EC 20 value of 2,4-D was reduced by approximately 40 % in the combinations. The NOEC's of the xenobiotics used in the combinations varied by a factor of 1,600 and depended strongly on the lipophilicity of the agents combined with 2,4-D. A significant statistical correlation of r = 0.90 was found between the NOEC's of the 15 combined xenobiotics and their lipophilicity. The combination effects on DNA synthesis were similar to those on cell growth. The regression lines of the relationship between the NOEC's and lipophilicity in both assays showed only slight differences in the slopes. This is an additional confirmation of our hypothesis on a facilitated uptake of 2,4-D in the binary combinations.

Suppression of growth-associated phosphorylation of proteins of fibroblasts by collagen fibrils.

Collagen fibrils suppressed serum- or epidermal growth factor (EGF)-inducible DNA synthesis of human fibroblasts. The phosphorylation of cellular proteins upon these mitogenic stimulation was analyzed by two-dimensional polyacrylamide gel electrophoresis in order to reveal a possible interference of collagen fibrils with the cellular mitogenic signal transduction pathway coupled with the protein phosphorylation-dephosphorylation reaction. Spots of phosphorylated proteins numbered 192 on plain plastic which were reduced to 143 on collagen fibrils. More than half of them were matched between the two substrates, most of which were much more weakly phosphorylated on collagen fibrils. EGF stimulated the phosphorylation of these proteins of cells on plastic. Among them a protein with an approximate molecular weight of 27K and an isoelectric point of 5.3 was early and highly responsive to EGF, phosphorylation of which seemed to be catalyzed mainly by protein kinase C and tyrosine kinase. Collagen fibrils significantly suppressed this phosphorylation. The present study demonstrates that collagen fibrils modulate the growth-associated protein phosphorylation of cells, which seems to lead to the suppression of DNA synthesis.

Transforming Growth Factor-β1 Has both Promoting and Inhibiting Effects on Induction of DNA Synthesis in Human Fibroblasts

Growth-arrested human normal fibroblasts, TIG-1, initiated DNA synthesis following addition of epidermal growth factor (EGF). Transforming growth factor-β1 (TGF-β1) by itself had no effect on induction of DNA synthesis. When EGF and TGF-β1 were added simultaneously to growth-arrested TIG-1 cells, induction of DNA synthesis was enhanced compared with that by EGF alone. Contrarily, when TGF-β1 was added earlier than 2 h or later than 2 h of EGF addition, induction of DNA synthesis was prevented. Induction of DNA synthesis by EGF was insensitive to pertusis toxin (PT, an inhibitor of Gi protein) and to staurosporine (a protein kinase inhibitor). The promoting effect of TGF-β1 on DNA synthesis was PT-insensitive and staurosporine-sensitive. Contrarily, inhibitory activity of TGF-β1 on DNA synthesis was PT-sensitive and staurosporine-insensitive. These studies suggest that the effect of TGF-β1 is to promote or to inhibit induction of DNA synthesis by EGF expressed through different signal transduction processes in the same cell.

Cyclin D1-mediated inhibition of repair and replicative DNA synthesis in human fibroblasts.

Cyclin D1 is a key regulator of the G1 phase of the cell cycle. Inhibition of cyclin D1 function results in cell cycle arrest, whereas unregulated expression of the protein accelerates G1. Cyclin D1 is localized to the nucleus during G1. We found that during repair DNA synthesis, subsequent to UV-induced DNA damage, G1 cells readily lost their cyclin D1 while the proliferating cell nuclear antigen (PCNA) tightly associated with nuclear structures. Microinjection of cyclin D1 antisense accelerated DNA repair, whereas overexpression of cyclin D1 prevented DNA repair and the relocation of PCNA after DNA damage. Coexpression of cyclin D1 with its primary catalytic subunit, Cdk4, or with Cdk2, also prevented repair. In contrast, coexpression of PCNA, which is also a cyclin D1-associated protein, restored the ability of cells to repair their DNA. Acute overexpression of cyclin D1 in fibroblasts prevented them from entering S phase. Again, these effects were abolished by coexpression of cyclin D1 together with PCNA, but not with Cdk4 or Cdk2. Altogether, these results indicate that down-regulation of cyclin D1 is necessary for PCNA relocation and repair DNA synthesis as well as for the start of DNA replication. Cyclin D1 appears to be an essential component of a G1-checkpoint.

Bradykinin inhibition of EGF- and PDGF-induced DNA synthesis in human fibroblasts.

Bradykinin exhibits proliferative influences in several types of cells; however, in the present study, bradykinin did not promote DNA synthesis but actually inhibited the DNA synthesis induced by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) in human gingival fibroblasts (HGF). This dose-dependent inhibitory effect was a specific intracellular interaction in that increasing concentrations of EGF did not counteract the inhibitory actions of bradykinin when added at 100 nM. The phosphoinositide-calcium signaling cascade is a likely point of interaction for the inhibitory influences of bradykinin; however, no interactions between bradykinin and EGF were observed with the generation of inositol phosphates or intracellular calcium fluxes. The inhibitory influences of bradykinin do not appear to be the result of a transmodulation of the EGF receptor, since EGF-mediated autophosphorylation was not negatively affected by bradykinin. Bradykinin-stimulated prostaglandin E2 (PGE2) release was potentiated by EGF, and, in the presence of indomethacin, the inhibition of the EGF-induced DNA synthesis by bradykinin was minimized. The results presented demonstrate that bradykinin can inhibit EGF- and PDGF-induced DNA synthesis and suggest that PGE2 synthesis is responsible for the observed bradykinin inhibition of EGF-induced DNA synthesis.

Action of ornithine α ketoglutarate on DNA synthesis by human fibroblasts

Ornithine alpha ketoglutarate (OKG) is largely used in clinical nutrition for its anabolic effects. However, the mechanism of its action remains questionable. We investigated the effect of OKG on the rate of DNA synthesis in human fibroblasts. The in vitro experimental procedure required to demonstrate in cell culture the anabolic effects of OKG observed in vivo was found to be glutamine-free and serum-poor medium with sparse cells. In these conditions, OKG induced a significant increase in [3H]thymidine incorporation compared to untreated control cells. This effect was dose-dependent and was observed in all the cultures tested. Taken individually, the two constituents of OKG, i.e. alpha KG and Orn, also showed a stimulatory effect, but did not demonstrate a dose-dependent response. Concomitant analysis of extracellular aminoacids showed in alpha KG-treated cultures an increase in glutamate and a decrease in aspartate, suggesting a cellular transamination of alpha KG. Glutamine, which is the preferential energetic substrate of fibroblasts, can be produced from glutamate and might play a role in the action of OKG. Moreover, OKG induced a rise in the cellular polyamine content. This, in association with the inhibitory effect on OKG action of difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, suggests a link between the polyamine biosynthesis pathway and the anabolic effect of OKG.

Identification of a Family of Insulin-Like Growth Factor II Secreted by Cultured Rat Epithelial-Like Cell Line 18,54-SF: Application of a Monoclonal Antibody

Somatomedin/insulin-like growth factor (IGF)-like polypeptides (designated SMP) were purified from the serum-free conditioned medium of cultured rat epithelial-like cells, 18,54-SF. A monoclonal antibody (MAb) was produced against partially purified SMP. The antibody was immunoglobulin G1 relatively specific for multiplication-stimulating activity III-2 (rat IGF-II), with a Kd value of 5.6 X 10(-9) M. The antibody showed 100% cross-reactivity with human IGF-II and 10% cross-reactivity with human IGF-I, but did not cross-react with insulin. For purification of SMP, therefore, immunoaffinity chromatography on Sepharose coupled with the MAb was used besides a procedure including ion exchange chromatography, gel filtration, and reverse phase HPLC. The purified SMP (at least five polypeptides) each gave a single peak on reverse phase HPLC and appeared as a single band with an apparent mol wt of 5000-8000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The major components of SMP (designated HP1-SMP and HP3-SMP), which were purified about 100-fold from conditioned medium, stimulated DNA synthesis in human fibroblasts in culture and sulfation in chick embryonic cartilage in culture. These polypeptides showed almost the same cross-reactivity as multiplication-stimulating activity III-2 on RIA with the MAb. The partial amino acid sequences of HP1- and HP3-SMP were determined, and these polypeptides were identified with rat IGF-II.

Induction of cyclic AMP synthesis by forskolin is followed by a reduction in the expression of c‐myc messenger RNA and inhibition of 3H‐thymidine incorporation in human fibroblasts

We have studied the effect of increased intracellular levels of cyclic AMP on the growth response to platelet-derived growth factor (PDGF) of human foreskin fibroblasts in culture. It was found that forskolin, a potent stimulator of adenylate cyclase activity, inhibits the stimulatory effect of PDGF on 3H-thymidine incorporation with a dose dependence similar to that observed with regard to cyclic AMP formation. A time-course study indicated that forskolin has no effect on ongoing DNA synthesis but affects events in the prereplicative phase. The cell-cycle block induced by forskolin was found to be reversible; after removal of the drug, DNA synthesis was initiated after a lag period, similar to that of the prereplicative phase of control cells. Forskolin had no effect on PDGF binding, receptor autophosphorylation, or c-fos mRNA expression. However, a reduction in PDGF-induced c-myc mRNA expression was observed in cultures given forskolin. Forskolin was also found to have a marked stimulatory effect on the expression of interferon-beta 2 mRNA expression. However, we were unable to demonstrate that the growth-inhibitory effect of forskolin is mediated by interferon-beta. In conclusion, an increase in cAMP levels leads to a reversible inhibition of PDGF-induced DNA synthesis in human fibroblasts, which may be related to an inhibition of c-myc mRNA expression.

Pancreatic secretory trypsin inhibitor as an acute phase reactant

Pancreatic secretory trypsin inhibitor (PSTI) in serum is an acute phase reactant and increases remarkably in response to surgical stress or invasion. The magnitude of the elevation of serum PSTI is far greater than that of acute phase reactants previously known. Recent investigations revealed that human PSTI stimulated DNA synthesis in human fibroblasts and that PSTI bound specifically to various cultured cells. These findings together with the result that PSTI or a polypeptide very similar to PSTI stimulated the growth of endothelial cells suggested that PSTI could possess previously unknown physiological function as a growth-stimulating hormone.

Electric stimulation of protein and DNA synthesis in human fibroblasts.

Human fibroblast cell cultures were employed as a model system to rapidly examine several potentially important variables involved in the use of high-voltage, pulsed galvanic stimulation (HVPGS) to increase the healing rate of soft tissue injuries. Fibroblasts were grown on Millipore filters and exposed to HVPGS of various voltages and pulse rates for 20 min in a rectangular, plastic chamber filled with growth medium. Filters with attached cells were placed either in the center of the chamber or close to the positive or negative electrode. Protein synthesis and DNA synthesis were monitored after stimulation using the radioactively labeled precursors, [3H]proline and [3H]thymidine, respectively. The major results obtained in this study are as follows: 1) the rates of both protein and DNA synthesis can be significantly increased by specific combinations of HVPGS voltage and pulse rate; 2) maximum stimulation of protein and DNA synthesis was obtained at 50 and 75 V, respectively, with a pulse rate of 100 pulses/s and the cells located near the negative electrode; and 3) exposure to HVPGS intensities greater than 250 V (at all pulse rates and locations within the chamber) is inhibitory for both protein and DNA synthesis. In view of the results obtained in preliminary clinical studies on the use of HVPGS for the treatment of dermal ulcers, it appears that similar voltages, pulse rates, and relative electrode location may be required for maximum acceleration of human skin wound healing.

The type II insulin-like growth factor receptor does not mediate deoxyribonucleic acid synthesis in human fibroblasts.

Two insulin-like growth factor (IGF) receptors, the type I and type II IGF receptors, have been described. While substantial evidence indicates that the type I receptor is involved in the regulation of cell division, it is uncertain if the type II receptor also mediates this response. Similarly, the role of the insulin receptor in mediating DNA synthesis remains controversial. To address these questions, we used a monoclonal antibody (alpha IR-3) to specifically inhibit type I IGF receptor activity and examined the effects of this inhibition on IGF- and insulin-stimulated DNA synthesis in human fibroblasts. WI-38 human embryonic lung fibroblasts have both type I and type II IGF receptors, as determined by cross-linking [125I] IGF-I and [125I]IGF-II to monolayers of these cells. In serum-free medium both IGF-I and IGF-II stimulate DNA synthesis in WI-38 fibroblasts, with half-maximal effects occurring at 1.5 +/- 0.3 (+/- SD) and 3.4 +/- 1.4 nM, respectively. At maximally effective concentrations, however, both hormones stimulate DNA synthesis to equal levels. alpha IR-3 binds to the type I, but not the type II, IGF receptor on WI-38 cells. It also inhibits IGF binding to the type I receptor on these cells. alpha IR-3 competitively inhibited both IGF-I- and IGF-II-stimulated DNA synthesis in WI-38 cells, but had no effect on either epidermal growth factor- or platelet-derived growth factor-stimulated DNA synthesis. These results indicate that in WI-38 fibroblasts the mitogenic effects of both IGF-I and IGF-II are mediated through the type I receptor and that the type II IGF receptor is not directly involved in this response. To define the role of the insulin receptor in mediating DNA synthesis we compared the effects of alpha IR-3 on insulin-stimulated DNA synthesis in a variety of human cell lines under identical experimental conditions. With WI-38 and HEL, another human embryonic lung fibroblast cell line, alpha IR-3 competitively inhibited the mitogenic effect of insulin. However, in two other fibroblast cell lines (GM498 and HES) and an osteogenic sarcoma cell line (MG63), alpha IR-3 inhibited IGF, but not insulin-stimulated DNA synthesis. These results indicate that human cell lines differ in the receptor type through which insulin stimulates DNA synthesis and that these differences are intrinsic properties of the cell lines and are not artifacts resulting from differences in experimental conditions.

1α, 25 — Dihydroxyvitamin D 3 modulates the growth of 3T3 cells and human skin fibroblasts stimulated by platelet-derived growth factor

We investigated the effect of 1α, 25 — dihydroxyvitamin D 3 (1,25 (OH) 2 vit D 3) on the H-thymidine uptake by Balb/c 3T3 cells and by human skin fibroblasts stimulated by normal human serum or by purified PDGF. We found an inhibitory effect of 1,25 (OH) 2 vit D 3 on the DNA synthesis of Balb/c 3T3 cells grown in the presence of human serum as well as in the presence of PDGF. At 5 % human serum this effect is minimal at 10 −12M 1,25 (OH) 2 vit D 3 and is maximal at 10 −9 M. On the DNA synthesis of human fibroblasts stimulated by human serum or by PDGF a modulatory effect of 1,25 (OH) 2 vit D 3 was shown. On these cells the vitamin had a stimulatory effect between 10 −11 and 10 −9 M and an inhibitory effect at very high concentrations (10 −7 M). Our results suggested that the effect of 1, 25 (OH) 2 vit D 3 on fibroblast DNA synthesis could be mediated by interactions with its specific intracellular receptor. 1,25 (OH) 2 vit D 3 had no any action on the growth of human fibroblasts stimulated by fibroblast growth factor.

Effect of an anti-insulin-like growth factor I receptor antibody on insulin-like growth factor II stimulation of DNA synthesis in human fibroblasts

To investigate the role of insulin-like growth factor II in the control of DNA synthesis in human fibroblasts, dose-response curves for insulin-like growth factor I and II stimulation of [3H]thymidine incorporation were compared in the absence and presence of alpha IR-3, a highly specific monoclonal antibody directed against the type I insulin-like growth factor receptor. Specific binding of [125I]insulin-like growth factor I to human fibroblast monolayer cultures was inhibited 60-70% in the presence of alpha IR-3. alpha IR-3 had no effect on [125I]insulin-like growth factor II binding to human fibroblasts. However, alpha IR-3 inhibited both insulin-like growth factor I and II stimulated [3H]thymidine incorporation. These data indicate that the type II insulin-like growth factor receptor does not function as a transducer of insulin-like growth factor II's mitogenic effect in human fibroblasts.

3-Aminobenzamide does not affect radiation-induced inhibition of DNA synthesis in human cells

3-Aminobenzamide (3AB), a potent inhibitor of poly(ADP-ribose) synthesis, does not affect the dose response for ionizing radiation-induced inhibition of DNA synthesis in human fibroblasts. If the radioresistant DNA synthesis observed in fibroblasts from patients with ataxia-telangiectasia (A-T) were due to reduced poly(ADP-ribose) synthesis after irradiation, as has been proposed, the response in normal cells incubated with 3AB would have been similar to that observed in A-T cells. Therefore, altered poly(ADP-ribose) synthesis in A-T cells is not solely responsible for their radioresistant DNA synthesis.

Sodium butyrate selectively inhibits host cell glycoprotein synthesis in human fibroblasts infected with cytomegalovirus

Host cell as well as viral DNA synthesis in human fibroblasts infected with human cytomegalovirus was found to be largely resistant even to high concentrations of sodium butyrate. Likewise, production of viral progeny was reduced by 1-2 orders of magnitude but not abolished. On the other hand, the drug allowed (modified) glycosylation only of viral polypeptides whereas that of host proteins was suppressed. Immunofluorescence studies on living cells suggested that butyrate may interfere with processing and intracellular transport of virus-specific surface membrane antigens.