Growth factor- and dexamethasone-induced proteins in Swiss 3T3 cells. Relationship to DNA synthesis

Dexamethasone-mediated androgen metabolism in human gingival and oral periosteal fibroblasts

Dexamethasone modulates the effects of other hormones and mediates cell function; the periodontium is a target tissue for androgens. It was therefore relevant to investigate the modulation of androgen metabolism by dexamethasone in cultured human gingival (HGF) and oral periosteal fibroblasts (HPF). Each cell line was incubated in Eagle minimum essential medium with [(14)C]testosterone/[(14)C]4-androstenedione as substrates and serial concentrations of dexamethasone (0.5-50 microg/ml), for 24h; the medium was solvent-extracted, analyzed and quantified for steroid metabolites. In response to dexamethasone, both HGF (n=6) and HPF (n=4) showed up to two-fold increases in the formation of 5alpha-dihydrotestosterone and 4-androstenedione (P<0.01, one-way ANOVA), and 3.6- to 5-fold increases in the formation of testosterone (P<0.001), from [(14)C]4-androstenedione, with some inhibition at higher concentrations. Dexamethasone stimulated the formation of physiologically active androgen metabolites in a dose-dependent manner. These metabolites might therefore contribute to dichotomous effects in connective tissues of the periodontium, dependent on effective concentrations of dexamethasone.

Two-dimensional gel analysis of secreted proteins induced by interleukin-1 beta in rat astrocytes

Interleukin-1 beta (IL-1 beta) is a pro-inflammatory cytokine produced in the brain by endogenous microglial cells responding to injury. Levels of IL-1 beta are elevated in several neurodegenerative disorders, including Alzheimer's disease. IL-1 beta, which can act as a mitogen for astrocytes, also elicits the expression and secretion of multiple factors and paracrine 'second messengers' such as other cytokines, nerve growth factor, prostaglandins and nitric oxide that may in turn modulate neuronal and glial responses to injury. Utilizing giant, high-resolution two-dimensional gel electrophoresis, we have sought to more fully define the potential range of protein mediators that are secreted by astrocytes treated with IL-1 beta. In cultured rat astrocytes, we observe dramatic increases in the secretion of eight different protein species after 24 h of treatment with human recombinant IL-1 beta (1 U/ml). Seven of the proteins are also induced by tumor necrosis factor-alpha or basic fibroblast growth factor. Based on immunoprecipitation with specific antisera, we have identified three of these proteins as plasminogen activator inhibitor type-1, ceruloplasmin, and complement component C3. The identities of the other proteins, including the IL-1 beta-specific induction, are currently unknown. Characterization of these downstream modulators of IL-1 beta action complements gene-based approaches and will provide a better understanding of astrocyte responses to injury as well as markers for astrocyte activation in neurodegenerative diseases.

Large-format, two-dimensional polyacrylamide gel electrophoresis of ovine periimplantation uterine luminal fluid proteins: identification of aldose reductase, cytoplasmic actin, and transferrin as conceptus-synthesized proteins

Early pregnancy in ruminants, such as the sheep, is characterized by relatively extensive development of the conceptus before attachment to the endometrium. Between the period of blastocyst hatching and initial attachment, the uterus responds to signals from the conceptus and adapts to provide an environment that permits the establishment of pregnancy. We used large-format two-dimensional (2D) PAGE to analyze the dynamic changes in protein composition of uterine luminal fluid (ULF) during this stage of pregnancy, and we determined the contribution of each of the extraembryonic membranes and the endometrium to these changes. The majority of the more than 40 pregnancy-associated proteins in ULF at Day 17 were secreted by the conceptus. By 2D gel map comparison and Western blotting, we identified transferrin, secreted by the yolk sac from Day 15, and cytoplasmic actin, one of the most abundant proteins produced by the trophoblast at Day 17. Apolipoprotein A1 and aldose reductase, whose abundance were markedly increased in pregnancy, were identified by peptide microsequencing. Aldose reductase, an enzyme required for the conversion of glucose to fructose, was shown to be synthesized by the trophoblast, and its detection even before the formation of the placenta suggests that the synthesis of fructose may occur much earlier than previously reported.

Leukoregulin induction of protein expression in human orbital fibroblasts: evidence for anatomical site-restricted cytokine-target cell interactions

The molecular basis for the profound inflammatory response and the accumulation of hyaluronan in orbital connective tissues seen in thyroid-associated ophthalmopathy is unknown. Moreover, the link between the orbital manifestations of Graves' disease and those in the pretibial skin, localized dermopathy, has yet to be established. We have reported recently that leukoregulin, an activated T lymphocyte-derived cytokine, dramatically induces hyaluronan synthesis and prostaglandin-endoperoxide H synthase 2 in human orbital fibroblasts in culture. In the current studies, utilizing giant two-dimensional gel electrophoresis, we find that orbital fibroblasts express constitutively a protein profile that distinguishes them from skin fibroblasts derived from the abdominal wall and from the pretibium. We further demonstrate that leukoregulin, when present in culture medium for 16 hr, up-regulates a set of orbital fibroblast proteins not present in untreated cultures or in fibroblasts from the abdominal wall. However, some of the same protein inductions are present in the pretibial fibroblasts. These leukoregulin-induced changes in protein expression are completely blocked by dexamethasone (10 nM). Our findings are the first to identify proteins that appear to be expressed and differentially regulated in an anatomical site-restricted manner in orbital and pretibial fibroblasts and seem to establish a molecular link between fibroblasts from the orbit and those in pretibial skin.

Glucocorticoid and phorbol ester effects in 3T3-L1 fibroblasts suggest multiple and previously undescribed mechanisms of glucocorticoid receptor-AP-1 interaction

A number of mechanisms have been proposed to account for glucocorticoid hormone and mitogen effects observed on the transcription of engineered exogenous target genes. However, the effect of the co-addition of these agents on the full range of endogenous responsive genes in a given cell type has not been addressed. We detected 19 metabolically labeled proteins or in vitro translation products whose synthesis was altered in 3T3-L1 fibroblasts in response to glucocorticoid hormone using two-dimensional electrophoresis on large-format gels. Co-addition of the mitogenic phorbol ester, tetradecanoylphorbolacetate (TPA), with glucocorticoid hormone resulted in independent (one species), synergistic (six species), and antagonistic (five species) effects on the glucocorticoid regulation of individual gene products, while seven other glucocorticoid regulated species were not affected. These and additional observations suggest direct and gene-specific effects of glucocorticoid receptor and AP-1 on the transcription of responsive genes, and for some of these genes the pattern of regulation is not accounted for by mechanisms described to date. In addition, the pattern of regulation of five species is consistent with a role in mediating the opposing physiological effects of glucocorticoid hormone and growth factors in these cells.

Corticosterone-responsive mRNAs in primary rat astrocytes

Glucocorticoids are important in neuronal development, regulation of the hypothalamic-pituitary-adrenal axis, adaptive behavior, and neuronal survival. Glia have receptors for glucocorticoid hormones and thus represent targets for hormone action in the brain. To identify mRNAs that are regulated by corticosterone in primary type 1 rat astrocytes, we have utilized ultra-high resolution giant two-dimensional gel electrophoresis of in vitro translated proteins. Our results reveal 12 in vitro translation products likely representing 10 mRNA species that are regulated by corticosterone. Eleven products are significantly increased and one decreased, most within 3 h of hormone treatment. Inclusion of cycloheximide does not prevent these changes, suggesting that they represent alterations in transcription; however, other mechanisms, such as changes in mRNA stability, cannot be excluded. Two corticosterone-regulated proteins were identified as glucocortin and glutamine synthetase. These two proteins are glucocorticoid-regulated in a variety of cell types, whereas the others appear to be astrocyte-specific. Future identification of these hormone-responsive mRNAs and proteins will help elucidate the molecular basis for glucocorticoid action in the CNS.

Platelet-derived growth factor and dexamethasone combined with a collagen matrix induce regeneration of the periodontium in monkeys

Platelet-derived growth factor (PDGF) and the glucocorticoid dexamethasone combined with a collagen carrier matrix (CM) induced regeneration of the periodontium in monkeys. Regeneration was stringently defined as: (1) new cementum, (2) new supra-crestal bone extending coronally from the residual alveolar interdental septum and (3) functionally-oriented periodontal ligament fibers attaching new cementum to new bone. A single application of PDGF/dexamethasone/CM or CM was placed in debrided lesions of experimental periodontitis displaying 3-5 mm of attachment loss associated with horizontal and angular bony defects. Regeneration, judged histologically by these criteria and quantified by computer assisted histomorphometry after 4 weeks, was present only in PDGF/dexamethasone/CM treated lesions and not in those treated with CM or debridement alone. PDGF/dexamethasone/CM induced 5-fold more new cementum and ligament, and 7-fold more supra-crestal bone than control treatments. The presence of substantial amounts of regenerated periodontium including increased height of the alveolar bone; fill of vertically resorbed interdental alveolar septa in PDGF/dexamethasone/CM treated lesions suggests that this combination may provide a new therapeutic agent for the regeneration of lesions of periodontitis associated with horizontal as well as angular bony defects.

Synergistic effects of dexamethasone on platelet-derived growth factor mitogenesis in vitro

Platelet-derived growth factor (PDGF) and insulin-like growth factor-I (IGF-I) interact to stimulate proliferation of fibroblasts in culture. Glucocorticoids variably effect the response of cultured fibroblasts to polypeptide growth factors. This study determined the effects of dexamethasone on growth-factor stimulation of gingival, periodontal ligament and pulp fibroblast proliferation in vitro. Cultures of quiescent, low-passage, human fibroblasts were treated for varying periods of time with transforming growth factor-beta 2 (TGF-beta 2), PDGF and IGF-I: (1) alone, (2) in combination with each other, (3) singly plus dexamethasone, (4) in combination plus dexamethasone. Combinations of human, recombinant PDGF and IGF-I (10-1000 ng/ml) induced significantly higher rates of cell proliferation than either factor alone. Dexamethasone at doses ranging from 10(-5) to 10(-8) M substantially enhanced cell proliferation induced by these combinations and by PDGF without IGF-I but not IGF-I alone. By 6 days after a single application, 2-3 times as many cells were present in the PDGF and dexamethasone cultures as compared to PDGF without IGF-I. TGF-beta 2 specifically blocked the effects of dexamethasone added to PDGF-stimulated cells. Collagen and non-collagenous protein synthesis was not affected by the addition of PDGF and IGF-I with or without dexamethasone. These data suggest that dexamethasone may substitute for IGF-I in PDGF stimulation of cell proliferation.

Giant two-dimensional gel electrophoresis: methodological update and comparison with intermediate-format gel systems

Two-dimensional (2-D) gel electrophoresis methods for separating complex mixtures of proteins have not changed fundamentally since their original description in the late 1970's. Nevertheless, 2-D gel resolution has improved substantially as a result of a series of incremental modifications. One of these was the development of the "giant-gel" format, using gels measuring at least 30 x 30 cm to provide the highest resolution 2-D gel system available. As originally described, this procedure has several important limitations: it requires custom-built equipment; it is expensive in terms of time, reagents, film and support matrices; and it generates gels which are difficult to manupulate, particularly for silver staining. This report describes modifications in the giant gel procedure to permit use of a commercially available gel apparatus and to obtain giant gels of improved mechanical strength suitable for silver staining. The resolution of giant gels is compared with that obtained using two systems currently being marketed for use by laboratories performing large numbers of 2-D gel analyses. The smaller format gels resolved fewer proteins, by 30-40%, compared with the giant gels. This difference in resolving power suggests that giant gels will continue to be useful in selected applications.

Non-classical antiestrogenic actions of dexamethasone in variant MCF-7 human breast cancer cells in culture

The aim of this work was to determine whether dexamethasone (Dex), a synthetic glucocorticoid, counteracts the stimulatory effects of estradiol (E2) on MCF-7 cells. We have shown that Dex inhibits in a dose-dependent fashion the estradiol-stimulated cell proliferation. This inhibition (ID50 congruent to 5-10 nM), which is complete at 100 nM Dex, is prevented by the antiglucocorticoid RU 486 and is clearly different from that found with trans-4-OH-tamoxifen because the inhibition due to a fixed concentration of Dex is not abolished by a high concentration of estradiol. This inhibitory effect displays some degree of specificity. Progesterone and the progestins R 5020 and ORG 2058 are without effect and Dex does not alter the triiodo-L-thyronine-stimulated cell growth. To characterize further the antiestrogenic action of Dex, the effects of this drug on specific responses to estradiol were studied. (1) Among the positive responses to estradiol two are prevented by Dex (the increase of concentration of progestin receptors and that of immunoreactive insulin-like growth factor I, IR-IGF-I, in conditioned medium) and two are insensitive to Dex (the enhancement of the secretion of 52,000 and 160,000 Mr proteins). (2) A negative response to estradiol (the down-regulation of estrogen receptor) is not prevented but rather accentuated by Dex. Thus, Dex counteracts the stimulatory effects of estradiol on the proliferation of MCF-7 cell variants characterized by progestin insensitivity. This non-classical antiestrogenic effect could be due in part to the attenuation of the E2-induced IR-IGF-I secretion and, less probably, to the accentuation of the down-regulation of E2 receptors. It could account for certain therapeutic and/or side effects of glucocorticoids on estrogen target cells.

Papillomavirus-associated inductions of cellular proteins in mouse C127 cells: correlation with the presence of open reading frame E2

Bovine papillomavirus type 1 (BPV-1) readily transforms mouse C127 cells, conferring the ability to grow in soft agar and to form tumors in athymic (nu/nu) mice. Electrophoresis of total cellular proteins from these BPV-transformed lines on ultra-high resolution, giant two-dimensional gels displays the presence of novel, papillomavirus-related protein phenotypes. Analysis of the established BPV-1-transformed C127 cell lines, ID13 and ID14, reveals a set of six proteins which are either absent or synthesized at extremely low levels in the parental cell line. One of these proteins is also present in v-ras-transformed C127 cells, but none of the others are found in cells transformed by a variety of viral oncogenes, including the polyomavirus middle T, v-mos, or v-fes. The genome of BPV-1 contains two separate open reading frames (ORFs), E5 and E6, which can act independently to transform C127 cells. In addition, trans-activator and repressor proteins encoded respectively by the full-length and carboxy-terminal E2 ORF regulate the level of expression of other BPV-1 genes. We examined 34 cell lines transformed by intact and subgenomic recombinant DNAs of BPV-1. Cells harboring BPV-1 DNAs engineered to eliminate the expression of ORFs E4, E5, E6, or E7 display five of the PV-associated proteins, but these proteins are not seen in lines lacking the full E2 ORF. Moreover, G418-selected nontransformed cells expressing E2 cDNA from an SV40 promoter exhibit these proteins at high levels. Surprisingly, these proteins are also present in cells containing BPV-1 DNAs with amino-terminal E2 deletions, suggesting that these PV-associated proteins represent novel cellular responses to a factor encoded within the E2-C gene region.

Rapid modulation of a 64 K dalton fibroblast protein: a PDGF mediated early cellular event

The results presented here reveal a novel platelet derived growth factor (PDGF) mediated early cellular event. Treatment of growth arrested Balb/c3T3 fibroblasts with PDGF induces a specific and rapid modulation of a 64,000 Dalton (64 KD) protein preexisting in quiescent cells. The kinetics of 64 KD protein modulation indicate that, temporally, this PDGF mediated step lies between the membrane associated immediate events such as receptor autophosphorylation or ion mobilization and the earliest known transcriptional event, the activation of the proto-oncogene c-fos.

Detection of glucocorticoid sensitive secretory proteins from human melanoma cells

NEL-M1 human melanoma cells have been established to grow in Ham's F12 medium in the absence of serum, hormones, and exogenous growth factors. Conditioned medium from NEL-M1 cultures stimulates growth of these same cells whereas glucocorticoids retard growth in the presence and absence of conditioned medium. Because recent reports indicate that glucocorticoids inhibit the synthesis of growth factors from a variety of cell types, we hypothesized that glucocorticoids may be inhibiting growth of NEL-M1 cells by either suppressing the synthesis of the autocrine growth factor or regulating other secretory proteins that may inhibit the activity of the autocrine growth factor. Initial studies were done to clearly show that NEL-M1 cells were growth inhibited, both in vivo and in vitro, when exposed to the synthetic glucocorticoid, triamcinolone acetonide (TA). When NEL-M1 cells were injected into nude mice and treated with TA (100 micrograms per mouse per week) a 67% reduction in tumor mass was observed compared to the control group over a 5-wk growth period. Additional studies show that in a serum-free defined medium TA (100 nM) inhibited growth of NEL-M1 cells by 56% after 6 d in culture. At this same time TA was shown to affect the expression of several proteins secreted from these cells. TA treatment resulted in the appearance of a 125,000 molecular weight protein, suppression of the synthesis-secretion of three proteins (37,000, 57,000, and 76,000 molecular weight) and enhanced expression of a 60,000-molecular weight protein. However when NEL-M1 cells were cultured in conditioned medium from TA-treated cells, a stimulation in both [3H]thymidine incorporation into DNA and cell proliferation was observed. When the conditioned medium was fractionated by Amicon ultrafiltration, the growth stimulatory activity was found in the less than 10,000 molecular weight fraction. These results demonstrate that glucocorticoids, as a single agent, inhibit the growth of NEL-M1 human melanoma cells. However, this growth inhibition by glucocorticoids may not be through the regulation of the synthesis-secretion of the autocrine growth factor. Furthermore, the data suggest that the glucocorticoid-sensitive secretory proteins may not be directly involved in the in vitro regulation of NEL-M1 cellular growth.

Maturation-related gene expression of rat astroblasts in vitro studied by two-dimensional polyacrylamide gel electrophoresis

Maturation of rat astroblasts was induced in vitro by acidic fibroblast growth factor (aFGF), hydrocortisone and dibutyryl cyclic AMP. Cells grown for 20 days were treated for 48 h and labelled with [35S]methionine only during the last 18 h of treatment. Cell proteins solubilized in lithium dodecyl sulfate were submitted to two-dimensional polyacrylamide gel electrophoresis. About 300 radioactive proteins could be analysed visually and compared. All treatments induced visible quantitative and sometimes qualitative changes. A total of 81 proteins had their rate of biosynthesis modified. For some proteins, this rate was changed by only one treatment, while for others it was changed by two or even by the three treatments, mostly in the same way. These results are consistent with the hypothesis that the proteins involved in the maturation process are organized in sets, proteins belonging to one set always being regulated together under a common control. Some sets would be regulated by only one effector while others would be regulated by several effectors.

Low-cost two-dimensional gel densitometry

A major obstacle to full utilization of the powerful technique of two-dimensional (2-D) gel electrophoresis is the expense and complexity of quantifying the results. Using an analog-to-digital converter already present in the widely available Commodore 64 or Commodore 128 microcomputer, we have developed a 2-D gel densitometer (GELSCAN) which adds only $20.00 to the cost of the Commodore system (currently around $700.00). The system is designed to work with autoradiograms of 2-D gels. Spots of interest are identified visually and then positioned manually over a light source. A pinhole photoelectric sensor mounted in a hand-held, Plexiglas holder, or "mouse," is briefly rubbed over each spot. Maximum density of the spot is determined and its value is converted to counts per minute via an internal calibration curve which corrects for the nonlinear response of film to radiation. Local spot backgrounds can be subtracted and values can be normalized between gels to adjust for variation in amount of radioactivity applied or in exposure time. Reproducibility is excellent and the technique has some practical as well as theoretical advantages over other more complicated approaches to 2-D gel densitometry. In addition, the GELSCAN system can also be used for scanning individual bands in 1-D gels, quantitation of "dot-blot" autoradiograms and other tasks involving transmission densitometry.