Cortisol decreases the concentration of translatable type-I procollagen mRNA species in the developing chick-embryo calvaria

Characterization of the continuous skin fibroblastoid cell line, WE-skin11f, from walleye (Sander vitreus)

A walleye dermal fibroblastoid cell line, WE-skin11f, was established and characterized. WE-skin11f was immunocytochemically positive for two known dermal fibroblast protein markers: vimentin and collagen I. At passage 26, WE-skin11f cultures contained both diploid and aneuploid populations. Ascorbic acid was required to produce extracellular collagen I fibres. Both of the skin fibroblastoid cell lines, WE-skin11f and rainbow trout-derived RTHDF, were not as good as the walleye caudal fin fibroblastoid cell line, WE-cfin11f, at forming abundant dense extracellular collagen matrices. The thermobiology of WE-skin11f was similar to that of other walleye cell lines with 26°C showing best temperature for growth and 4°C showing no growth but 100% viability. The transcript levels of b2m and mhIa genes of the major histocompatibility class I receptor in WE-skin11f were largely similar at all temperatures examined (4, 14, 20 and 26°C). Cortisol had a variety of effects on WE-skin11f cells: growth inhibition, morphological change from fibroblastoid to epithelioid, and enhancement of barrier function. Treatment of WE-skin11f cells with the physiologically relevant concentration of 100 ng/ml cortisol inhibited collagen I synthesis and matrix formation. Thus, WE-skin11f cell line could be useful in fish dermatology, endocrinology, and immunology research.

A tissue-culture model for the study of canine vocal fold fibroblasts

A tissue-culture model has been developed for the study of fibroblasts from the canine vocal fold. Laryngeal tissue (lamina propria) obtained from euthanized dogs is rinsed, cut into 1-mm3 pieces, and incubated in 5% carbon dioxide at 37 degrees C. A confluent monolayer is established within several days. Detectable levels of elastin in the tissue culture supernatant are measured by an indirect enzyme-linked immunosorbent assay. Various external agents have been shown to affect elastin production. The effects of KTP laser irradiation, hydrocortisone (1.3 mumol/L), transforming growth factor-beta (10 ng/mL), and human leukocyte elastase have been measured. Thus the canine vocal fold fibroblast tissue culture is established as a model for further investigations to improve wound healing and to understand the wound-healing process following laryngeal microsurgery.

Peptide growth factors and wound healing

Growth factors and cytokines are important signal transducers in wound microenvironments. Experimental data are accumulating rapidly which demonstrate their ability to influence populations of polymorphs and macrophages to migrate to the wound, subsequently to be replaced by synthetic cells which produce collagen and matrix; these events are controlled sequentially at cell receptor level by a variety of locally delivered (paracrine and autocrine) peptides. Preliminary results from clinical trials using recombinant human growth factors to improve cutaneous healing are encouraging. Current research aims to produce growth preparations which can be applied to a wound to accelerate healing.

Effect of long-term PUVA treatment of psoriasis on the collagen and elastin gene expression and growth of skin fibroblasts in vitro

The proliferation rate, collagen metabolism and collagen and elastin messenger-RNA levels were studied in fibroblasts derived from patients who had received many courses of either systemic 8-methoxypsoralen or topical trioxsalen PUVA treatment. The proliferation rate of fibroblasts as measured by the incorporation of 3H-thymidine or by cellular division was decreased in those obtained from patients who had PUVA treatment as compared with controls. Collagen synthesis was slightly increased in the cells from PUVA-treated patients, but the relative collagen synthesis and the ratio between types I and III collagen were unchanged. The levels of collagen and elastin mRNAs were increased in fibroblasts derived from the PUVA-treated patients. No significant differences in histology or immunochemistry could be found in the biopsies taken from topical and systemic PUVA-treated patients.

Cyclic AMP-dependent inhibition of collagen synthesis in avian epiphyseal cartilage cells: effect of chicken and human parathyroid hormone and parathyroid hormone-related peptide

Avian cartilage cells derived from epiphyseal growth-plate and avian skin fibroblasts were cultured in vitro. Production of cAMP by cartilage cells was stimulated by the synthetic fragments (1-34) of chicken (cPTH), human (hPTH) parathyroid hormone and by parathyroid hormone-related peptide (PTHrP). The enhancement of cAMP production by any of the peptides could be blocked by the parathyroid hormone analogue (3-34)PTH, suggesting interaction with PTH specific receptors. When incubated with [3H]proline, both cell types released radiolabelled collagenase-digestible and non-digestible proteins into the medium. cPTH, hPTH, PTHrP, forskolin, prostaglandin E2 (PGE2) and 8-bromo cAMP inhibited collagen production in cartilage cells with only minor effects on non-collagenase digestible proteins. No effect of cAMP on collagen production by fibroblasts was observed. The present results provide additional evidence that avian growth-plate cartilage cells are targets for PTH, and are first to demonstrate the response of a non-mammalian system to mammalian PTHrP. The data suggest that collagen production by epiphyseal growth-plate cartilage cells is inhibited by PTH and that this inhibition is mediated by cAMP.

Epidermal growth factor (EGF) prevents methylprednisolone-induced inhibition of wound healing

Subcutaneously implanted cylindrical hollow viscose cellulose sponges were used to study the effect of locally applied epidermal growth factor (EGF) on methylprednisolone-induced inhibition of granulation tissue formation in rats. In in vivo studies the sponges were treated immediately after implantation with a single injection of 2 mg (approximately 1.7 x 10(-3) M) of depot methylprednisolone or with its carrier solution only. Thereafter the implants were injected daily with 5 micrograms of EGF or with its carrier solution 0.1% albumin for 7 days. Methylprednisolone treatment decreased the accumulation of nucleic acids, collagen, and glycosaminoglycans in the developing granulation tissue. After daily injections of EGF the concentrations of these tissue components returned close to the control values. In cultures of rat granulation tissue fibroblasts, 10(-4) M and 10(-3)M methylprednisolone decreased collagen synthesis by 41 and 81% from the control level, respectively. In the presence of methylprednisolone EGF treatment could not increase collagen synthesis of fibroblasts. Methylprednisolone treatment resulted in a dose-dependent reduction in pro alpha 1(I) collagen mRNA levels, which was partially inhibited by low EGF concentrations (1 and 10 ng/ml). In the presence of methylprednisolone all concentrations of EGF increased fibronectin mRNA levels in a dose-dependent manner. It is concluded that EGF treatment can prevent the inhibitory effect of methylprednisolone on wound healing by stimulating fibroblast proliferation but does not stimulate collagen synthesis per cell.

Comparison of the effects of dexamethasone and 13-cis-retinoic acid on connective tissue biosynthesis in human skin fibroblasts

The effects of glucocorticoids and retinoids on connective tissue biosynthesis were studied in cultured human skin fibroblasts (HSFs). More specifically attention was paid to the effects of dexamethasone and 13-cis-retinoic acid (RA) on total protein and collagen synthesis and on collagen and fibronectin mRNA levels. The results indicated that dexamethasone reduced the relative collagen synthesis and collagen mRNA levels in HSFs and increased the total incorporation of proline into proteins, the latter effect being due to increased activity in the intracellular proline pool. 13-cis-RA did not affect collagen synthesis at the concentration studied (10(-7) M) but it did reduce the corresponding mRNA levels. Simultaneous addition of both dexamethasone and 13-cis-RA or etretinate resulted in the largest decrease in type I and type III procollagen mRNA levels, indicating that retinoids do not oppose the effect of glucocorticoids on collagen synthesis in cultured HSFs. For comparison the effects of dexamethasone and 13-cis-RA on the mRNA levels of another extracellular matrix component, fibronectin, and of a constitutive enzyme, glyceraldehyde-3-phosphate dehydrogenase, were also studied. The results indicated, that dexamethasone treatment did not alter fibronectin mRNA levels in HSFs, while 13-cis-RA did so to a marked extent. Both dexamethasone and 13-cis-RA also reduced the mRNA level of glyceraldehyde-3-phosphate dehydrogenase, indicating that glucocorticoids and retinoids have both similar and different effects on gene expression in HSF.

Modulation of collagen metabolism by glucocorticoids. Receptor-mediated effects of dexamethasone on collagen biosynthesis in chick embryo fibroblasts and chondrocytes

The steroid modulation of collagen metabolism was studied by injecting chick embryos with dexamethasone in vivo, and collagen synthesis was subsequently assayed by pulse-labeling the tissue with [14C]proline in vitro. The synthesis of [14C]hydroxyproline in tendons and sterna from chick embryos treated with dexamethasone was markedly reduced as compared with untreated controls. The inhibition of [3H]hydroxyproline synthesis was accompanied by a similar reduction in type I and II procollagen mRNA levels, as detected by Northern blot and dot blot hybridizations with chick pro alpha 1(I), pro alpha 2(I) and pro alpha 1(II) sequence specific cDNAs. The reduction in type II procollagen mRNA level was shown to be dose dependent. Control experiments indicated that the post-translational hydroxylation of prolyl residues was only slightly decreased in dexamethasone treated animals, and that the specific activity of the intracellular free proline pool and the intracellular degradation of collagen were unchanged. To address the mechanisms of the inhibition of collagen biosynthesis, specific binding of dexamethasone to glucocorticoid receptors in chick embryo tendon and cartilage cells was studied in a whole cell assay using [3H]dexamethasone as the ligand. Matrix-free tendon and cartilage cells had approximately 19,000 and 15,000 receptor sites per cell, respectively, and the binding affinities (Kd) for dexamethasone in tendon and cartilage cells were 2.9 x 10(-9) and 2.3 x 10(-9) M. Comparable values were obtained using a cytosol binding assay. The nuclear binding of dexamethasone in tendon and cartilage cells were similar. The results suggest that the dexamethasone-induced inhibition of collagen production is primarily due to decreased levels of functional procollagen mRNA, possibly resulting from receptor-mediated inhibition of the gene expression on the transcriptional level.

Collagen gene expression in keloids: analysis of collagen metabolism and type I, III, IV, and V procollagen mRNAs in keloid tissue and keloid fibroblast cultures

Regulation of collagen gene expression was studied in keloids and fibroblast cultures established from keloid biopsies from 9 patients. The collagen concentration in keloid tissue was not different from that in normal skin. The activities of 2 enzymes catalyzing intracellular collagen biosynthesis, prolyl 4-hydroxylase (PH) and galactosylhydroxylysyl glucosyltransferase (GGT) were significantly elevated in the keloids, the mean increase in the former enzyme being 5-fold and in the latter 3-fold with respect to the controls. The mean procollagen production rate in the keloid fibroblasts was at the control level, with only 1 keloid cell line showing a procollagen synthesis rate higher than the mean value + 2 SD of the controls. The mean PH and GGT activities of the keloid fibroblasts were not elevated, but PH activity in 2 cell lines and GGT activity in 1 cell line were higher than the mean + 2 SD for the controls. Cellular type I, III, IV, and V procollagen mRNAs were measured by slot blot hybridization using specific human cDNA clones for the various collagen types. The amounts of type I, III, and V procollagen mRNAs corresponded to the ratios in which these collagen types are produced by fibroblasts. No synthesis of type IV procollagen mRNA by keloid fibroblasts was observed. The total amount of type I and III procollagen mRNAs correlated significantly (p less than 0.01) with the procollagen synthesis rate measured after radioactive labeling of the cells in the keloid and control fibroblasts, indicating that collagen production in these cells is mainly controlled by regulating the final steady state levels of collagen mRNA. The results suggest that fibroblasts isolated from keloids often synthesize normal amounts of collagen.

Preventive effect of malotilate on carbon tetrachloride-induced liver damage and collagen accumulation in the rat

Malotilate is a new drug suggested for use in chronic liver diseases. It is shown here to prevent liver damage caused by CCl4. The concomitant administration of malotilate with CCl4 significantly decreased hydroxyproline accumulation in the liver, liver prolyl 4-hydroxylase and liver and serum galactosylhydroxylysyl glucosyltransferase activities. However, it had no effect on the daily urinary hydroxyproline excretion or the hydroxyproline content of the skin, liver or lungs in normal young growing rats. It also had no specific inhibitory effect on hydroxyproline synthesis or secretion in fibroblast cultures, and did not affect the amount of procollagen-alpha 1(I)-specific mRNAs in these cultures. Thus it seems to have no direct inhibitory effect on collagen metabolism. In addition to inhibition of liver collagen accumulation, malotilate was also able to prevent the development of morphological changes in the liver such as focal necrosis, fatty infiltration and inflammatory changes. It also normalized almost completely the standard liver-function tests. It is possible that malotilate may prevent excessive collagen deposition by inhibiting the inflammation caused by CCl4-induced liver damage.

Dexamethasone modulates the metabolism of type IV collagen and fibronectin in human basement-membrane-forming fibrosarcoma (HT-1080) cells

The effect of dexamethasone on the synthesis and degradation of type IV collagen was studied in human fibrosarcoma cells, HT-1080. A dexamethasone concentration as low as 0.1 microM markedly increased collagen synthesis in HT-1080 cells labelled with [14C]proline. The increase in type IV collagen synthesis was not specific, since total protein synthesis was also increased. Further studies indicated that part of the increase was due to an increase in the specific radioactivity of the intracellular proline pool, after dexamethasone treatment. In fact, with dexamethasone concentrations of 0.1-10 microM the relative collagen synthesis was decreased, indicating that synthesis of other protein was increased more than that of type IV collagen. This was also confirmed by measuring the relative amount of type IV collagen RNA by using recombinant plasmid cDNA specific for the human procollagen pro alpha l (IV) RNA. The results indicated that relative collagen synthesis and the relative amount of type IV collagen messenger RNA was decreased similarly, indicating that dexamethasone affected type IV collagen synthesis at the pre-translational level. The dexamethasone-induced effect on total protein and collagen synthesis was maximal after 12-24 h. Dexamethasone induced a marked accumulation of collagen into the cell layer, leading to diminished deposition of soluble collagen into the medium. Since bacterial-collagenase treatment of the cell layer drastically decreased the collagen content of the dexamethasone-treated cells, this indicates that dexamethasone caused an accumulation of collagen into the extracellular matrix of the cell layer. In contrast, the amount of fibronectin was markedly increased in the medium. Dexamethasone decreased the type IV collagen-degrading activity in HT-1080 cells. The HT-1080 cells contained glucocorticoid receptors, as demonstrated by two different methods: by a whole-cell binding assay and by using a cytosol-gel-filtration method. The number of specific binding sites was similar to that in human skin fibroblasts. In conclusion, glucocorticoids affect the metabolism of type IV collagen and fibronectin in HT-1080 cells, and, since these cells contain specific glucocorticoid receptors, the effects are apparently receptor-mediated.

Gene expression of type I, III and IV collagens in hepatic fibrosis induced by dimethylnitrosamine in the rat

Dimethylnitrosamine (DMN)-induced hepatic fibrosis was used as an experimental model to study collagen-gene expression during liver fibrogenesis. Increase in the concentrations of the mRNAs for type I, III, and IV collagens was found to be an early event in the development of hepatic fibrosis, as the mRNAs for all three collagen types showed a definite increasing tendency by day 7 of DMN treatment. Prolyl 4-hydroxylase (EC 1.14.11.2) and galactosylhydroxylysyl glucosyltransferase (EC 2.4.1.66) activities were also distinctly elevated at this stage, whereas no increase could be detected in the liver collagen content. The increase in the mRNAs for type I collagen was the smallest and that for type IV collagen the greatest at all the time points studied. The relative concentrations of the mRNAs for the three collagen types on day 21 of DMN treatment were 350% of the control mean for type I collagen, 490% for type III and 660% for type IV. The data further indicate that the proportions of the mRNAs for the three collagen types are 1.0:0.9:0.2 in normal rat liver, 1.0:1.4:0.8 on day 14 of DMN treatment, and 1.0:1.3:0.5 on day 21. The early marked increase in the mRNA for type IV collagen suggests that enhanced production of basement-membrane collagen may be an early event in the development of hepatic fibrosis.

Elevated pro alpha 2(I) collagen mRNA levels in cultured scleroderma fibroblasts result from an increased transcription rate of the corresponding gene

Fibroblasts cultured from affected and unaffected skin sites of three scleroderma patients were studied for the activation of type I collagen gene expression. Dot blot hybridizations with pro alpha 2(I) collagen specific cDNA probe revealed 2.9-4.8-fold increases in pro alpha 2(I) mRNA levels in the affected fibroblasts over the unaffected control cells. Transcription rate of the pro alpha 2(I) gene in the nuclei isolated from the same cells was 2.0-3.7-fold higher in the scleroderma fibroblasts than in the controls. The results show that scleroderma fibroblasts have undergone activation of collagen gene expression at the transcriptional level, which subsequently results in elevated procollagen mRNA levels, overproduction of collagen, and development of dermal fibrosis.

Transforming growth factor-beta increases steady state levels of type I procollagen and fibronectin messenger RNAs posttranscriptionally in cultured human dermal fibroblasts

Transforming growth factor-beta (TGF beta), when injected subcutaneously into newborn mice, induces a rapid fibrotic response, stimulates chemotaxis, and elevates the rates of biosynthesis of collagen and fibronectin by fibroblasts in vitro. We explored the molecular mechanisms of TGF beta-mediated stimulation of collagen and fibronectin synthesis in cultured human foreskin fibroblasts. TGF beta preferentially stimulated the synthesis of fibronectin and type I procollagen chains 3-5-fold as shown by polypeptide analysis. Concomitant elevation in the steady state levels of messenger RNAs (mRNAs) coding for type I procollagen and fibronectin also occurred but without a net increase in the rate of transcription of either of these genes. The preferential stabilization of mRNAs specifying type I procollagen and fibronectin provides a partial explanation for the mechanisms by which TGF beta enhances the synthesis of type I procollagen and fibronectin in mesenchymal cells.

Necrobiosis lipoidica: ultrastructural and biochemical demonstration of a collagen defect

Ten patients with necrobiosis lipoidica lesions were studied. Five patients had diabetes mellitus. The age of the patients varied from 15 to 73 years and the duration of the skin lesions was from 2 to 20 years. Histologically, the lesions were characterized by degeneration of collagen and elastin. In some lesions elastin fibers could be seen in areas devoid of normal-looking collagen. Electron microscopy revealed loss of cross-striation of collagen fibrils and a marked variation in the diameter of individual collagen fibrils. The concentration of collagen, measured by assay of hydroxy-proline, a collagen-specific amino acid, was markedly decreased in the lesional skin, but the ratio of type I/III collagen was unchanged in the affected skin. Fibroblasts established from affected skin synthesized less collagen than cells derived from healthy-looking skin. The decreased collagen synthesis was due to a decreased amount of messenger RNA for type I procollagen, measured by hybridization with a specific human cDNA clone. The production of collagenase by these fibroblasts was not increased. Our results thus indicate that in necrobiosis lipoidica lesions, collagen fibrils are defective and the amount of collagen is reduced, probably due to decreased synthesis of collagen by affected fibroblasts.

Age differences in the effect of hydrocortisone on the synthesis of insoluble elastin in aortic tissue of growing chicks

Glucocorticoids have been shown by others to increase the synthesis of elastin both in aortic tissue of embryo chicks and in cells derived from fetal ligamentum nuchae. This report describes the effects of hydrocortisone on the production of elastin in aortic tissue of developing chick embryos and chicks. While the effect of hydrocortisone on elastin synthesis is stimulatory in the 14 day chick embryo and the day-old chick, the same dose of this glucocorticoid has no effect on elastin production in the 7 day old chick and significantly inhibits synthesis of elastin in the 14 day old chick. These age-related alterations in elastin production in response to hydrocortisone cannot be attributed to an effect of the steroid on the pool size of the radioactively labelled amino acid used to measure elastin synthesis.

Altered steady-state ratio of type I/III procollagen mRNAs correlates with selectively increased type I procollagen biosynthesis in cultured keloid fibroblasts

Regulation of collagen gene expression was studied in fibroblast cultures established from patients with keloids, fibrotic lesions of the skin. In selected keloid fibroblast cultures, an overproduction of type I procollagen was observed. This increase was accompanied by a parallel increase in type I procollagen-specific mRNA levels, as detected by dot-blot and RNA transfer hybridizations, without concomitant change in type I procollagen gene copy number. At the same time, type III procollagen mRNA levels were unaltered, resulting in markedly elevated type I/III procollagen mRNA ratios. Thus, keloid fibroblasts offer a unique model to study the independent regulation of the gene expression of two genetically distinct procollagens, type I and type III.

Modulation of glucocorticoid receptor activity by cyclic nucleotides and its implications on the regulation of human skin fibroblast growth and protein synthesis

The modulation of glucocorticoid receptor activity by cyclic nucleotides was studied in cultured human skin fibroblasts. The receptors appeared to be activated in the presence of dibutyryl-cAMP and inactivated by dibutyryl-cGMP. Significantly, the cGMP content of the fibroblasts increased during cell growth, with a concomitant decrease in the glucocorticoid receptor activity, while when the cells reached early confluency the decrease in cGMP content was accompanied by an increase in cAMP and increased activity of the glucocorticoid receptors. In addition, cortisol induced (2'-5')oligoadenylate synthetase in these cells and raised the cellular (2'-5')oligoadenylate concentrations. This resulted in a decrease in both DNA and protein synthesis activity in the cells, a response which correlated with the (2'-5')oligoadenylate concentration. The combination of cortisol and dibutyryl-cAMP had a synergetic stimulatory effect on the (2'-5')oligoadenylate concentration and a synergetic inhibitory effect on protein synthesis. In conclusion, it is demonstrated here that cyclic nucleotides can modulate glucocorticoid receptor activity in cultured human skin fibroblasts, and thus these compounds may indirectly affect cellular metabolism by regulating the cellular responses to glucocorticoids.

Increased type I collagen mRNA levels in cultured scleroderma fibroblasts

Pro alpha 1(I)collagen mRNA levels in fibroblasts cultured from affected and non-affected skin areas of two scleroderma patients were measured by hybridization of RNA blots with a specific cDNA clone. Collagen synthesis was estimated with an inhibition ELISA for type I collagen and with densitometric scans of fluorograms of [3H]proline-labelled medium proteins. Affected scleroderma fibroblasts exhibited 2-7-fold higher levels of pro alpha 1(I)collagen mRNAs to account for the increased synthesis of collagen by the same cells. This suggests that the control of collagen synthesis in scleroderma is altered at transcriptional level.

Glucocorticoids stimulate collagen and noncollagen protein synthesis in cultured vascular smooth muscle cells

The effect of glucocorticoids on collagen synthesis was examined in cultured bovine aortic smooth muscle (BASM) cells. BASM cells treated with 0.1 microM dexamethasone during their proliferative phase (11 d) were labeled with [3H]proline for 24 h, and the acid-precipitable material was incubated with bacterial collagenase. Dexamethasone produced an approximate twofold increase in the incorporation of proline into collagenase-digestible protein (CDP) and noncollagen protein (NCP) in the cell layer and medium. The stimulation was present in both primary mass cultures and cloned BASM. An increase in CDP and NCP was detected at 0.1 nM, while maximal stimulation occurred at 0.1 microM. Only cells exposed to dexamethasone during their log phase of growth (1-6 d after plating) showed the increase in CDP and NCP when labeled 11 d after plating. The stimulatory effect was observed in BASM cells treated with the natural bovine glucocorticoid, cortisol, dexamethasone, and testosterone, but was absent in cells treated with aldosterone, corticosterone, cholesterol, 17 beta-estradiol, and progesterone. The increase in CDP and NCP was absent in cells treated with the inactive glucocorticoid, epicortisol, and totally abolished by the antagonist, 17 alpha-hydroxyprogesterone, suggesting that the response was mediated by specific cytoplasmic glucocorticoid receptors. Dexamethasone-treated BASM cells showed a 4.5-fold increase in the specific activity of intracellular proline, which was the result of a twofold increase in the uptake of proline and depletion of the total proline pool. After normalizing for specific activity, dexamethasone produced a 2.4- and 2.8-fold increase in the rate of collagen and NCP synthesis, respectively. Cells treated with dexamethasone secreted 1.7-fold more collagen protein in 24 h compared to control cultures. The BASM cells secreted 70% Type I and 30% Type III collagen into the media as assessed by two-dimensional gel electrophoresis. The ratio of these two types was not altered by dexamethasone. The results of the present study demonstrate that glucocorticoids can act directly on vascular smooth muscle cells to increase the synthesis and secretion of collagen and NCP.

Cortisol decreases the cellular concentration of translatable procollagen mRNA species in cultured human skin fibroblasts

The effect of cortisol on the cellular concentration of translatable procollagen mRNAs was studied in cultured human skin fibroblasts. Cortisol selectively decreased the amount of procollagen mRNAs, in comparison to the total mRNA activity, when the cells were grown in enriched medium conditions, i.e., with 10% newborn calf serum. The selective decrease was first observed after 6 h exposure to 1 microM cortisol. In depleted medium conditions, i.e., with 2% newborn calf serum, the initial response was a stimulatory one, followed after about 12 h by a decrease in the procollagen mRNA activity. The results suggest that the selective inhibitory effect of cortisol on the cellular concentration of translatable procollagen mRNA species needs an optimal serum concentration. Furthermore, the results give support to the hypothesis that the decrease in the procollagen mRNA concentration after cortisol administration is a secondary response, preceded by the induction of some intracellular regulation system.

Glucocorticoid effects on thymidine incorporation into the DNA of S49 lymphoma cells

The effects of glucocorticoids on lymphoid cell growth and thymidine incorporation into DNA were studied using the S49 mouse lymphoma cell line. Glucocorticoid-mediated lymphocytolysis in these cells is preceded by an arrest in the G1 phase of the cell cycle [1]. However, this arrest is only partial, and is reversible by washing out the hormone. Thus, although the overall impression is that these cells are arrested in G1 and then begin to die, they apparently can escape the arrest and proceed through the cell cycle, albeit at a relatively low level. The mode of DNA synthesis in these glucocorticoid-treated cells is replicative and not repair. The importance of the inhibition of thymidine incorporation to the cell death process in S49 cells is evident from experiments in which cells are treated with both the hormone and various DNA synthesis inhibitors; a synergistic killing of the cells is obtained. Thus, the inhibition of DNA synthesis and cell proliferation is a rapid, and perhaps primary effect of glucocorticoids on the complex process of hormone-mediated lymphocytolysis in this mouse cell line.

DNA fragmentation in S49 lymphoma cells killed with glucocorticoids and other agents

The effects of glucocorticoids on DNA integrity in the mouse S49 lymphoma cell line were assessed. DNA cleavage at the internucleosomal regions was observed, and this response was correlated to the dose of hormone used and the time of treatment. Also, an apparent steroid specificity was observed: internucleosomal cleavage was associated only with treatment of the cells with glucocorticoids. Cells treated with dibutyryl cyclic AMP (which also causes lymphocytolysis) also exhibited DNA cleavage. However, when cells were killed with various DNA synthesis inhibitors and other lethal agents, the same DNA cleavage pattern was observed. Furthermore, new protein synthesis did not seem to be required, since cells killed with puromycin and cycloheximide also exhibited internucleosomal DNA fragmentation. Although DNA fragmentation may not be a specific early effect of glucocorticoid-mediated lymphocytolysis, it may be the final, irrevocable step in this complex process.

A rapid and sensitive assay for protein disulphide isomerase activity

An assay procedure for the determination of protein disulphide isomerase activity is presented. The method is based on the reactivation of randomly cross-linked RNAase, the extent of RNAase reactivation being determined from the degradation of radioactively labelled RNA. The method is rapid and sensitive and allows one to test a large number of samples simultaneously.