Post-transcriptional regulation of rat liver gene expression by glucocorticoids

Chronic ethanol consumption upregulates the cytosolic and plasma membrane sialidase genes, but down regulates lysosomal membrane sialidase gene in rat liver

We have previously shown that chronic ethanol feeding stimulates liver cytosolic sialidase (CS) and plasma membrane sialidase (PMS), whereas it decreases lysosomal membrane sialidase (LMS) activities with concomitant alterations in their relative synthetic rate in rat. To understand the molecular mechanism(s) for these changes, we have evaluated the effect of ethanol administration in male Wistar rats as a function of increasing dietary ethanol concentration after 8 weeks of pair-feeding on (i) the expression of CS, PMS, and LMS genes by real-time quantitative polymerase chain reaction method; (ii) their relative transcription rates by nuclear run-on assay; and (iii) the actual amount of these sialidase proteins in the liver fractions of the respective groups by Western blot method. We have demonstrated that the animals fed with 10.6%, 20.8%, and 36% of total calories as ethanol showed a 20% (P<.05), 34% (P<.01), and 69% (P<.01) increase in CS mRNA level, and 22% (P<.05), 26% (P<.01), and 47% (P<.01) increase in PMS mRNA level, but a decrease in LMS mRNA level by 35% (P<.05), 50% (P<.01), and 80% (P<.01), respectively, as compared to controls. Western blot analyses of CS, PMS, and LMS in the liver subfractions showed that changes in protein levels of CS, LMS, and PMS were consistent with the corresponding changes in the respective mRNA levels. Thus, the upregulation of CS and PMS, but not LMS which is down regulated by chronic ethanol, may account for the appearance of asialoconjugates in alcoholics.

Dexamethasone stimulates transcription of the Na+-K+-ATPase beta1 gene in adult rat lung epithelial cells

Na+-K+-ATPase plays an essential role in active alveolar epithelial fluid resorption. In fetal and adult alveolar epithelial cells, glucocorticoids (GC) increase Na+-K+-ATPase activity and mRNA levels. We sought to define the mechanism of Na+-K+-ATPase gene upregulation by GC. In a rat alveolar epithelial cell line (RLE), dexamethasone (Dex) increased beta1-subunit Na+-K+-ATPase mRNA expression two- to threefold within 3 h after exposure to the GC. The increased gene expression was due to increased transcription as demonstrated by nuclear run-on assays, whereas mRNA stability remained unchanged. Transient transfection of 5' deletion mutants of a beta1 promoter-reporter construct demonstrated a 1.5- to 2.2-fold increase in promoter activity by Dex. All of the 5' deletion constructs contained partial or palindromic GC regulatory elements (GRE) and responded to GC. The increased expression of promoter reporter was inhibited by RU-486, a GC receptor (GR) antagonist, suggesting the involvement of GR. The palindromic GRE at -631 demonstrated Dex induction in a heterologous promoter construct. Gel mobility shift assays using RLE nuclear extracts demonstrated specific binding to this site and the presence of GR. We conclude that GC directly stimulate transcription of Na+-K+-ATPase beta1 gene expression in adult rat lung epithelial cells through a GR-dependent mechanism that can act at multiple sites.

Alkaline phosphatase expression in tissues from glucocorticoid-treated dogs

OBJECTIVE

To determine the effect of glucocorticoids on the induction of alkaline phosphatase (ALP) isoenzymes in the liver, kidneys, and intestinal mucosa, 3 tissues that are principally responsible for ALP synthesis in dogs.

SAMPLE POPULATION

Tissues from the liver, kidneys, and intestinal mucosa of 6 dogs treated with 1 mg of prednisone/kg/d for 32 days and 6 untreated control dogs.

PROCEDURES

Using canine-specific primers for the ALP isoenzymes, a reverse transcription-polymerase chain reaction assay was designed to measure liver ALP (LALP) and intestinal ALP (IALP) mRNA and heterogeneous nuclear RNA (hnRNA) expression in tissues from the liver and kidneys and intestinal mucosa of glucocorticoid-treated and control dogs. Tissue ALP isoenzyme activities were compared between the groups.

RESULTS

The LALP activity and mRNA concentrations increased in tissues of the liver and kidneys in dogs treated with prednisone, whereas LALP hnRNA increased only in liver tissues. The IALP activity and mRNA expression increased in intestinal mucosa and liver tissues in prednisone-treated dogs. We did not detect an increase in IALP hnRNA expression in these tissues.

CONCLUSIONS AND CLINICAL RELEVANCE

Synthesis of ALP is increased in the liver, kidneys, and intestinal mucosa of dogs in response to prednisone treatment. This response appears to be regulated at the transcriptional level, but mechanisms may differ between LALP and IALP.

Dexamethasone stimulates ribosomal protein L32 gene transcription in rat myoblasts

Incubation of rat L6 myoblasts for 24 h with 10(-7) M dexamethasone, a glucocorticoid analogue, resulted in a 2.5-fold increase in the rate of ribosomal protein L32 (rpL32) gene transcription with a corresponding increase in the level of rpL32 mRNA. The increased rate of transcription was accompanied by a dramatic enhancement in binding of the delta, but not beta and gamma, factors to the rpL32 gene promoter as measured by gel mobility shift assays. This increased binding reflects a change in the activity of the delta factor since its level is unchanged by dexamethasone treatment. The presence of the glucocorticoid analogue RU38486 reversed the stimulating effect of dexamethasone on rpL32 gene transcription and binding of the delta factor to the delta element. These results suggest that the mechanism which enhances rpL32 gene transcription in dexamethasone-treated rat L6 myoblasts involves glucocorticoid-receptor mediated changes in the activity of the delta factor.

Dexamethasone induces lipocalin-type prostaglandin D synthase gene expression in mouse neuronal cells

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is responsible for the production of PGD(2), the main PG in the CNS. PGD(2) is an endogenous sleep inducer, and it is involved in the control of odor and pain responses and body temperature. In addition, PGD synthase transports lipophilic molecules in the subarachnoid space and CSF. By northern and western assays we show that the synthetic glucocorticoid dexamethasone, an inhibitor of PG production in most tissues, induces L-PGDS mRNA and protein in a dose- and time-dependent fashion in mouse neuronal GT1-7 cells. Accordingly, dexamethasone increases cellular L-PGDS enzymatic activity. Dexamethasone induced L-PGDS gene transcription in run-on assays and activated the mouse L-PGDS gene promoter in transiently transfected cells. It is interesting that the tumor promoter 12-O-tetradecanoyl-phorbol 13-acetate (TPA), which induces the synthesis of PGs in many tissues, inhibited the increase in L-PGDS expression induced by dexamethasone. In contrast, neither dexamethasone nor TPA affected the expression of cyclooxygenases-1 and -2. Our data demonstrate that dexamethasone induces L-PGDS gene transcription in neuronal cells.

Up-regulation of the low density lipoprotein receptor-related protein by dexamethasone in HepG2 cells

Dexamethasone has been shown to decrease the expression of the low density lipoprotein (LDL) receptor, but its effect on other members of the LDL receptor family is not known. We studied the effect of dexamethasone in HepG2 cells on the expression of the LDL receptor family members using radiolabeled receptor associated protein (RAP) which binds to all the members of the family. Treatment of HepG2 cells with increasing concentrations of dexamethasone resulted in a 2-fold increase in the binding and degradation of RAP. To identify the receptor responsible for the increased binding and degradation of RAP, we used specific ligands. For LDL receptor, we used LDL itself. For the LDL receptor-related protein/alpha 2-macroglobulin receptor, we used activated alpha 2-macroglobulin. The binding of LDL to HepG2 cells was decreased, whereas binding and degradation of activated alpha 2-macroglobulin was increased by 2-fold suggesting that dexamethasone increased LRP expression. Increased LRP expression was positively correlated with the increase in the steady-state levels and transcript numbers of the LRP mRNA; no changes in RAP or gamma-actin mRNA levels were observed. Increased mRNA levels were not due to an increased rate of transcription of the gene as assessed by nuclear run-on experiments. These studies indicate that dexamethasone increases cell-surface LRP activity in HepG2 cells by increasing the steady state mRNA levels and suggest that post-transcriptional mechanisms play a role in controlling LRP mRNA levels.

Internalization and nuclear localization of peptide hormones

The presence of neuropeptide receptors on the plasma membrane is well accepted, as is its internalization and down-regulation. The analysis of the fate of these peptides within their target-cells is difficult. Endogenous peptides or administered native peptides are visualized in these cells using immunocytology after cryoultramicrotomy. Labelled peptides can be injected and their internalization kinetics studied using ultrastructural autoradiography. The pituitary gland is a suitable model for the study of the neuropeptide mechanism, with the lactotroph function being taken as an example in the present case. Prolactin (PRL) release depends on two main neuropeptides: thyrotropin-releasing hormone (TRH) and somatostatin (SS). The TRH immunoreactivity obtained from endogenous as well as injected material was restricted to the plasma membrane, secretory granules, cytoplasmic matrix and nucleus. The internalization kinetics of exogenous native TRH showed an increase of immunoreactive material in all compartments including the nucleus. The endogenous SSs (SS14 and SS28) were detected in the same subcellular lactotroph compartments. Injection of 125I-SS showed a rapid binding of SS at the plasma membrane level before internalization. For 60 min of in vivo uptake, 125I-SS28, the large SS molecule, was detected in the cytoplasm only, while 125I-SS14 was found in the nuclear matrix. In vitro 125I-SS28 was restricted to the nuclear membrane. Under physiological conditions the endogenous neuropeptides were visualized in the nucleus, but after injection of labelled peptides only small molecules were found in the nucleus. The significance of the presence of these neuropeptides is discussed.

Effect of dexamethasone and phenobarbital on run-on transcription rate and CYP3A mRNA concentration in rat liver: changes during development

Modulation of CYP3A1 and CYP3A2 mRNA expression by dexamethasone and by phenobarbital has been studied in immature (21-day-old) and adult (90-day-old) rat liver. Positive modulation of these forms by both agents markedly declines with the age of the animals. However, CYP3A2 mRNA, although physiologically extinguished in the adult females, still responds to dexamethasone stimulation. The regulatory mechanisms underlying the differential behavior of CYP3A1 in the immature and adult animals have been further investigated by analyzing the early changes in the run-on transcription rates and the subsequent mRNA accumulation in the liver in response to the inducer agents. CYP3A genomic clones were constructed and characterized for this purpose. The use of a unique cosCYP/3A1 intronic sequence, identified in this work, made possible the selective determination of the transcription rate of this gene by run-on assay, as a function of ontological development and inducer treatment. Parallel determination of the mRNA concentration in the liver by dot blot analysis demonstrated that dexamethasone induces CYP3A1 essentially through transcription regulation in immature animals, while in adults it is suggested to act mainly at a post-transcriptional level.

Hormonal regulation of the nuclear localization signals of the human glucocorticosteroid receptor

Nuclear localization of the rat glucocorticosteroid receptor (rGR) transiently expressed in COS-7 cells appears to be mediated by two nuclear localization signals, NL1 and NL2, in a hormone-dependent mechanism. We investigated the intracellular distribution of the human GR (hGR) expressed in COS-7 cells, by a different immunohistochemical technique involving immunostaining of cell pellet sections, thus avoiding the use of cell permeabilizing agents and allowing rigorous comparison between successive experiments. With a large set of hGR mutants, we could define determinants of the hGR nuclear localization and compare them with those previously reported for rGR. Our study demonstrated two hormone-dependent nuclear localization signals. NL1 activity, overlapping the DNA-binding domain (DBD)-hinge boundary, was repressed by the unliganded ligand-binding domain (LBD), even if the repressed NL1 retained a residual potency to target hGR in the nucleus. Structure/function analysis suggested a bipartite structure of NL1, analogous to that of other nuclear targeting signals (the carboxy-terminal part of DBD between amino acids 478 and 487 and the beginning of the hinge region which includes a basic amino acid stretch between 491 and 498). Upon hormone binding, NL2, located in the LBD, was activated, but was unable by itself to sustain full nuclear localization, which required the derepressed NL1 activity. Only two sequences in the LBD, localized between amino acids 600 and 626 and from amino acid 696 up to the carboxyl-terminal amino acid 777, respectively, were found to inhibit NL1 activity. As previously reported, efficient nuclear retention, mandatory for gene expression, did not required DNA-binding activity. The controversial intracellular localization of the unliganded form of hGR and the role of hsp90 in cytoplasmic localization are further discussed.

Glucocorticoids modulate the induction of BLTE/granzyme A activity in the murine T cell hybridoma PC60

The cytolytic granule-associated serine esterase granzyme A cleaves the synthetic substrate benzyloxycarbonyl-L-lysinate-thiobenzylester (BLT) and has been described as a marker for cytotoxic T lymphocyte (CTL) activation. We recently showed that BLT-esterase activity (BLTE activity) can be induced in the murine CTL-hybridoma PC60 by exogenous interleukin-1 (IL-1) and/or a rise of the intracellular cAMP level, although cAMP does not act as a second messenger for IL-1 in this system. The present study demonstrates that glucocorticoids (GC) such as dexamethasone and hydrocortisone efficiently inhibit the induction of BLTE activity by IL-1 and/or cAMP and downregulate the basal BLTE levels in PC60 cells; these results could be reproduced in part with progesterone and were steroid class-specific, since estrogen did not affect the induction of BLTE activity. The GC-induced effects on the production of BLTE activity required the activation of specific GC receptors, since induction of the activity could be restored upon addition of the contragestative drug RU 38486; they further could not be related to any alteration of the cellular metabolism of arachidonic acid and did not appear to be mediated by secreted macromolecules such as lipocortins.

Regulation of protein kinase C gene expression by retinoic acid in B16 mouse melanoma cells

We have previously shown that the retinoic acid (RA)-induced growth arrest and differentiation of B16 mouse melanoma cells is accompanied by a large increase in the amount and activity of protein kinase C (PKC). Since PKC is a multigene family, we investigated which isoforms were expressed in control and RA-treated B16 melanoma cells, and characterized the manner by which RA regulates PKC gene expression. We found that RA treatment of B16 cells resulted in an increase in PKC alpha mRNA beginning at 4-8 h and reached a maximum of 10- to 12-fold over control levels by 48 h. There was also a small amount of PKC gamma mRNA, present only in 48-h RA-treated cells, but no PKC beta mRNA was detected. The effect of RA on PKC alpha mRNA induction was not direct since the induction was abolished when cycloheximide was included in the incubation medium. Nuclear run-on experiments showed that the RA-induced increase in PKC alpha steady-state mRNA was not entirely due to an increase in transcriptional activity, as the increase in PKC alpha transcription was only 2- to 3-fold over control, which is not enough to account for the 10- to 15-fold increase in steady state levels. There was also no change in PKC alpha mRNA stability in RA-treated B16 cells compared to untreated cells. The 10.9-kb PKC alpha message in both control and RA-treated cells was less stable than the 3.8-kb PKC alpha message. Therefore, we propose that the major level of control of PKC alpha mRNA levels by RA is post-transcriptional, either RNA processing or transport out of the nucleus.

Biological effects of glucocorticoid hormones on two rat colon adenocarcinoma cell lines

Glucocorticoid hormones are thought to play a role in carcinogenesis as they regulate cell differentiation and proliferation. We have investigated the effect of dexamethasone on two cell lines derived from a colon carcinoma, which differ by their tumorigenicity. Dexamethasone was found to inhibit growth of both the progressive (PROb) and the regressive clone (REGb). Upon glucocorticoid treatment, PROb cells were found to secrete an additional Mr approximately 40,000 protein. The synthesis and the release in the culture medium of this protein is stimulated specifically by glucocorticoid agonists, and not by other steroid hormones. The anti-glucocorticoid RU 38486 is inefficient and suppresses the induction of this protein by dexamethasone. Induction is sensitive to actinomycin D, suggesting that regulation may be related to an alteration of the rate of mRNA synthesis. The cellular effect of glucocorticoid hormones being mediated through a specific soluble receptor, we have characterized this protein. The PROb cells contained more specific glucocorticoid-binding sites (approximately 170,000 sites per cell) than the regressive ones (REGb cells; approximately 100,000 sites per cell). In both clones, the receptor was associated with the Mr approximately 90,000 heat shock protein to yield large complexes (Stokes radius Rs approximately 7.5 nm), which were dissociated to the same extent upon heat- and salt-treatment. The steroid- and DNA-binding unit of the receptor, characterized under denaturing conditions using an anti-receptor monoclonal antibody, was found to be more degraded in the PROb cell line.

Effect of interferon-gamma on complement gene expression in different cell types

We have studied the expression of the complement components C2, C3, factor B, C1 inhibitor (C1-inh), C4-binding protein (C4-bp) and factor H in human peripheral blood monocytes, skin fibroblasts, umbilical vein endothelial cells (HUVEC) and the human hepatoma cell line G2 (Hep G2) in the absence and the presence of interferon-gamma (IFN-gamma). E.l.i.s.a. performed on culture fluids, run-on transcription assays, Northern blot and double-dilution dot-blot techniques confirmed that monocytes expressed all six components, whereas fibroblasts, HUVEC and HepG2 each expressed five of the six components. Fibroblasts and HUVEC did not synthesize C4-bp, and Hep G2 did not produce factor H. In addition to these differences, the synthesis rates of C3, C1-inh and factor H were not the same in all cell types. However, the synthesis rates of C2 and factor B were similar in all four cell types. The half-lives of the mRNAs were shorter in monocytes than in other cell types. Monocyte factor H mRNA had a half-life of 12 min in monocytes, compared with over 3 h in fibroblasts and HUVEC. The instability of factor H mRNA in monocytes may contribute to their low factor H secretion rate. IFN-gamma produced dose-dependent stimulation of C2, factor B, C1-inh, C4-bp and factor H synthesis by all cell types expressing these proteins, but decreased C3 synthesis in all four cell types. Cell-specific differences in the response to IFN-gamma were observed. The increased rates of transcription of the C1-inh and factor H genes in HUVEC were greater than in other cell types, while the increased rate of transcription of the C2, factor B and C1-inh genes in Hep G2 cells was less than in other cell types. IFN-gamma did not affect the stability of C3, factor H or C4 bp mRNAs, but increased the stability of factor B and C1-inh mRNAs and decreased the stability of C2 mRNA. Although these changes occurred in all four cell types studied, the half-life of C1-inh mRNA in monocytes was increased almost 4-fold, whereas the increases in the other cell types were less than 30%. These data show that the constitutive synthesis rates of complement components may vary in the different cell types. They also show that the degree of change in synthesis rates in response to IFN-gamma in each of the cell types often varies due to differences in transcriptional response, sometimes in association with changes in mRNA stability.

Modulation of complement gene expression by glucocorticoids

The addition of dexamethasone, prednisolone or cortisol (in order of efficacy) to human monocytes in culture produced dose-related increases in the synthesis rates of the complement components C1 inhibitor (C1-inh), factor B (B) and C2. In contrast, concentrations of C3 and lysozyme in the culture supernatants were decreased. Indomethacin stimulated synthesis of C1-inh, C2 and B, but had little effect on synthesis of C3 or lysozyme. The simultaneous addition of cycloheximide (2.5 micrograms/ml) abrogated the effects of dexamethasone on synthesis of C2, B and C1-inh, but the effect of indomethacin on the synthesis of these components was unchanged. These data suggest that protein synthesis is required for the effects of glucocorticoids on the synthesis of C2, B and C1-inh to occur. Dexamethasone and indomethacin increased the abundances of C1-inh mRNA, B mRNA and C2 mRNA in parallel with changes in the synthesis rates of these proteins. The changes in mRNA abundance were not transcriptional, but were shown to be due to increased mRNA stability. In contrast, dexamethasone decreased the expression of C3 and lysozyme by decreasing the rate of transcription of these genes. Indomethacin had no effect on transcription of the C3 and lysozyme genes. The half-lives of C3 mRNA, lysozyme mRNA and actin mRNA were not altered by dexamethasone or indomethacin. It is concluded that the effects of glucocorticoids on monocyte synthesis of C2, B and C1-inh are due to increased mRNA stability and may be related to inhibition of prostaglandin synthesis, as these effects are similar to those produced by indomethacin. The effects of dexamethasone on the synthesis of C3 and lysozyme differ from those on C2, B and C1-inh as they depend upon a decrease in gene transcription, which is not affected by indomethacin.

A secreted Mr approximately 40,000 glycoprotein specifically induced by glucocorticoids in a rat colon carcinoma cell line

Glucocorticoid hormones are thought to play a role in carcinogenesis, as they regulate cell differentiation and proliferation. We have previously shown that dexamethasone inhibits the growth of a rat colon carcinoma cell line, and induces the secretion of an Mr approximately 40,000 protein. We now report that the synthesis and the release in the culture medium of this protein is stimulated specifically by glucocorticoid agonists, and not by other steroid hormones. The anti-glucocorticoid RU 38486 is inefficient and suppresses the induction of this protein by dexamethasone. Induction is sensitive to actinomycin D, suggesting that regulation may be exerted by altering the rate of mRNA synthesis. Characterization of culture medium from dexamethasone-treated cells revealed that the Mr approximately 40,000 protein is glycosylated, and can be further separated from other secreted proteins by high-performance anion-exchange chromatography.

Control of HILDA/LIF gene expression in activated human monocytes

In the present study we have investigated some of the mechanisms involved in HILDA/LIF gene expression in activated human monocytes and compared them to those of G-CSF gene expression, another monocyte-derived cytokine. In the absence of added stimuli, HILDA/LIF mRNA was barely detectable in monocytes. HILDA/LIF mRNA accumulation was weakly induced by stimuli such as LPS or phorbol ester alone, and in a synergistic manner when they were used in combination with 1,25-dihydroxyvitamin D3. Nuclear run-on transcription analysis in U937 cells did not detect an increase of HILDA/LIF gene transcription upon phorbol ester and 1,25-dihydroxyvitamin D3 stimulation. Posttranscriptional control of HILDLA/LIF mRNA levels by an increase in mRNA half-life was demonstrated in the synergy between phorbol ester and 1,25-dihydroxyvitamin D3 and in the superinduction of HILDA/LIF transcript accumulation when CHX was added to stimulated cells shortly before cell harvesting. HILDA/LIF mRNA expression was largely inhibited when U937 cells were treated with CHX either at the onset or 4 h after the beginning of the stimulation period. When CHX was added 2 h before cell harvesting, a superinduction of mRNA accumulation was obtained. G-CSF mRNA accumulation showed a different pattern of response to the same stimuli, in particular a higher rate of response to LPS. In contrast to HILDA/LIF, an augmentation of G-CSF gene transcription was detected in activated monocytic cells when compared to controls. These studies indicate that HILDA/LIF gene expression by phorbol ester- and 1,25-dihydroxyvitamin D3-treated human monocytes has a relatively specific regulation, as compared to G-CSF gene expression, and that it is largely dependent on posttranscriptional mechanisms probably acting through labile, newly synthesized proteins.

RNA processing is a limiting step for murine tumor necrosis factor beta expression in response to interleukin-2

We have previously reported that tumor necrosis factor beta (TNF beta) expression is induced by interleukin-2 (IL-2) in the murine lymphocytic T-cell line CTLL-2. In this study, we have characterized the nuclear and cytoplasmic TNF beta transcript and assessed their role in TNF beta gene expression. A unique feature of TNF beta expression was the accumulation of nuclear precursors, which reflected a slow nuclear RNA processing. As a consequence, there was a delay in the appearance of cytoplasmic messengers after the transcriptional induction of TNF beta by IL-2. We also found that two messengers, the fully spliced messenger and an intron 3-retaining messenger, were exported to the cytoplasm and actively translated. The same pattern of expression was observed in concanavalin A-stimulated splenocytes, although the level of expression was much lower than in CTLL-2 cells. The simple genetic structure and the high level of accumulation of nuclear precursors make TNF beta a particularly attractive model system to use for studies of RNA processing and cytoplasmic transport of partially spliced messengers.

Interferon-mediated transcriptional and post-transcriptional modulation of complement gene expression in human monocytes

The addition of lymphoblastoid interferon alpha, fibroblast interferon beta and recombinant interferon gamma to in vitro monocyte cultures produced dose-dependent increases in transcription rates of the genes encoding the second component of complement (C2), factor B (B) and C1 inhibitor, and the abundance of their respective mRNA. Interferon gamma was the most effective at stimulating transcription of the C1-inhibitor gene whereas interferons alpha and beta were more effective at increasing the transcription of the C2 and B genes. Transcription of the C3 gene was reduced by interferon gamma. None of these cytokines altered the level of transcription of the actin gene. Interferon-induced changes in the levels of transcription of the C2, B and C1-inhibitor genes occurred rapidly, with significant changes occurring within 30 min of exposure to these cytokines. Within 4 h of removal of the interferons from the culture fluid, the level of transcription of the C1-inhibitor, C2, B and C3 genes returned to control values, as did abundance of C2, B and C3 mRNA. However, the abundance of C1-inhibitor mRNA remained elevated in interferon-gamma-treated monocytes. Combinations of interferons produced less than additive effects on the stimulation of the transcription of C2, B and C1-inhibitor genes, whereas measurements of C1-inhibitor mRNA and B mRNA showed that interferon gamma acted synergistically with interferon gamma to increase the abundance of the mRNA. Their effects on C2 mRNA abundance were less than additive. The half-lives of C1-inhibitor, C2, B and C3 mRNA were not altered by interferon alpha, whereas interferon gamma shortened the half-life of C2 mRNA by approximately 50%, and prolonged the half-lives of B and C1-inhibitor mRNA approximately twofold and fivefold, respectively. The half-life of C3 mRNA was unaltered by either interferon. These results show that the large increase in C1-inhibitor synthesis which occurs in interferon-gamma-treated monocytes, is due to a combination of increased transcription and increased C1-inhibitor mRNA stability. They also suggest that the synergistic effects of interferon alpha together with interferon gamma on C1-inhibitor and factor B synthesis is also dependent upon increased transcription and increased mRNA stability.

Interferon-induced transcriptional and post-transcriptional modulation of factor H and C4 binding-protein synthesis in human monocytes

Cultured human monocytes synthesize factor H (H) and C4 binding protein (C4-bp), as assessed by measuring their presence in culture fluids, and demonstrating the presence of their corresponding mRNAs in total monocyte RNA by Northern blot analysis and by nuclear run-on experiments. H mRNA (4.3 kb and 1.8 kb) could only be detected when cycloheximide (2.5 micrograms/ml) was present in monocyte culture fluid. Recombinant interferon-gamma (IFN-gamma) and lymphoblastoid interferon-alpha (IFN-alpha) produce dose-related increases in the synthesis of H and C4-bp and in the abundance of C4-bp mRNA (2.5 kb). Increased abundance of H mRNA was also seen when cycloheximide (2.5 micrograms/ml) was present in the cultures. Both cytokines increased the transcription rates of the H and C4-bp genes. These changes in transcription were rapid, with significant increases being observed within 30 min of exposure. Following the removal of the cytokines from the cultures the transcription rates of both genes returned to control levels within 4 h. The effects of combining IFN-alpha and IFN-gamma on H and C4-bp transcription rates, mRNA abundances and protein secretion rates were not quantitatively additive. The half-life of H mRNA in monocytes was 15 min, whereas that of C4-bp mRNA was 2 h 45 min. Neither half-life was altered by IFN-gamma.

RNA processing is a limiting step for murine tumor necrosis factor beta expression in response to interleukin-2

We have previously reported that tumor necrosis factor beta (TNF beta) expression is induced by interleukin-2 (IL-2) in the murine lymphocytic T-cell line CTLL-2. In this study, we have characterized the nuclear and cytoplasmic TNF beta transcript and assessed their role in TNF beta gene expression. A unique feature of TNF beta expression was the accumulation of nuclear precursors, which reflected a slow nuclear RNA processing. As a consequence, there was a delay in the appearance of cytoplasmic messengers after the transcriptional induction of TNF beta by IL-2. We also found that two messengers, the fully spliced messenger and an intron 3-retaining messenger, were exported to the cytoplasm and actively translated. The same pattern of expression was observed in concanavalin A-stimulated splenocytes, although the level of expression was much lower than in CTLL-2 cells. The simple genetic structure and the high level of accumulation of nuclear precursors make TNF beta a particularly attractive model system to use for studies of RNA processing and cytoplasmic transport of partially spliced messengers.

Modulation by interferons of the expression of monocyte complement genes

Interferons-alpha, -beta and -gamma (IFNs-alpha, -beta and -gamma) stimulated the synthesis of the second complement component (C2), Factor B (B) and C1 inhibitor (C1-inh) by human monocytes in vitro. The degree of increase of the secretion rates of C2, B and C1-inh was dose-dependent and proportional to increases in the abundances of their respective mRNAs. IFN-gamma was the most effective at stimulating monocyte C1-inh synthesis, whereas IFN-alpha and IFN-beta were marginally more effective at stimulating monocyte C2 and B synthesis. Kinetic studies showed that the effect of the IFNs was rapid, with maximum stimulation occurring within 1-2 h for all three proteins. After the removal of IFNs from cultures the C1-inh mRNA abundance remained elevated for over 24 h in IFN-gamma-treated monocytes but returned to control levels within 8 h in IFN-alpha-treated and IFN-beta-treated monocytes. The abundances of C2 mRNA and B mRNA also returned to basal values within 8 h after removal of any of the three cytokines from the cultures. Both IFN-alpha and IFN-beta acted synergistically with IFN-gamma to stimulate synthesis of C1-inh and B. This synergistic effect only occurred when the cytokines were present in the cultures simultaneously. The effects of IFN-gamma plus IFN-alpha or IFN-beta on C2 synthesis appeared to be additive rather than synergistic. IFN-gamma inhibited synthesis of C3 by monocytes, but IFN-alpha and IFN-beta had no effect on the synthesis of this protein. Furthermore, none of the three cytokines had any effect on the expression of actin mRNA in monocytes.

A difference in the regulation of mRNA expression between the phenotypic and the embryonic alkaline phosphatase genes in human cancer cells

The steady-state levels of mRNAs encoding alkaline phosphatase isoenzymes were examined in two human breast carcinoma cell lines. MDA-MB-157 cells expressed the phenotypic breast alkaline phosphatase and BT20 cells expressed the nonphenotypic placental alkaline phosphatase isoenzyme, frequently reexpressed in neoplasms. Dexamethasone (DEX), which elicits a general effect on phosphatase expression, and 1,25-dihydroxy vitamin D3 (1,25(OH)2D3), a promoter of cell differentiation that correspondingly effects embryonic phosphatase expression, were chosen as perturbing agents for these experiments. RNA blot analysis showed a single RNA species of approximately 2.6 kb under all treatment conditions in BT20 cells and a single RNA species of 2.6 kb under each condition in MDA-MB-157 cells. The results showed that the expression of both the AP isoenzyme mRNA phenotypic of breast produced by MDA-MB-157 cells and the embryonic alkaline phosphatase isoenzyme (PLAP) mRNA produced by BT20 cells was increased by treatment with DEX. By comparison 1,25(OH)2D3 caused an increase in the tissue-unspecific AP mRNA in the MDA-MB-157 cells, but caused a decrease in PLAP mRNA levels in BT20 cells. The level of each isoenzyme mRNA species is altered by either hormone in a dose- and time-dependent manner in both cell lines. In BT20 cells, treatment with cycloheximide showed that ongoing protein synthesis is not required to potentiate the PLAP mRNA response to DEX, but is required for the action of 1,25(OH)2D3. However, protein synthesis is required for the action of both hormones in the MDA-MB-157 cells which make the breast phenotypic AP. These data demonstrate that the DEX- and 1,25(OH)2D3-regulated expression of both of these alkaline phosphatase isoenzymes occurs via a complex mechanism involving control of mRNA abundance, not translational control of constant message levels.

Mechanism of glucocorticoid regulation of alkaline phosphatase gene expression in osteoblast-like cells

In the rat osteosarcoma cell line ROS 17/2.8, glucocorticoids increase the activity of the plasma membrane enzyme, alkaline phosphatase. To determine the mechanisms responsible for this effect, we have studied the actions of dexamethasone on alkaline phosphatase activity, immunoreactive protein, and steady-state mRNA levels. Dexamethasone treatment increased both specific activity of alkaline phosphatase and the cell surface expression of immunoreactive protein in a dose-dependent manner, with a half-maximal increase at 2 nM. Steady-state alkaline phosphatase mRNA levels were also increased in a dose-dependent manner. The time course of dexamethasone induction occurred relatively slowly, with a lag period of 12 h before any discernable effect on alkaline phosphatase mRNA levels. The rise in alkaline phosphatase mRNA levels was attributable entirely to changes in gene transcription, with no effect on message stability. Treatment of ROS 17/2.8 cells with actinomycin D completely abolished the dexamethasone-induced rise in alkaline phosphatase mRNA levels. Measurement of alkaline phosphatase mRNA degradation, by incubation of cells with the transcriptional inhibitor 5,6-dichloro-ribofuranosylbenzimidazole, indicated an apparent half-life of 24 h in both untreated and dexamethasone-stimulated cells. The protein synthesis inhibitors cycloheximide and puromycin blocked the dexamethasone induction of alkaline phosphatase mRNA. These data suggest that the dexamethasone-induced rise in alkaline phosphatase gene transcription requires the synthesis of an unknown mediator protein.

Translational initiation factor expression and ribosomal protein gene expression are repressed coordinately but by different mechanisms in murine lymphosarcoma cells treated with glucocorticoids

P1798 murine lymphosarcoma cells cease to proliferate upon exposure to 10(-7) M dexamethasone and exhibit a dramatic inhibition of rRNA and ribosomal protein synthesis (O. Meyuhas, E. Thompson, Jr., and R. P. Perry, Mol. Cell Biol. 7:2691-2699, 1987). These workers demonstrated that ribosomal protein synthesis is regulated primarily at the level of translation, since dexamethasone did not alter mRNA levels but shifted the mRNAs from active polysomes into inactive messenger ribonucleoproteins. We have examined the effects of dexamethasone on the biosynthesis of initiation factor proteins in the same cell line. The relative protein synthesis rates of eIF-4A and eIF-2 alpha were inhibited by about 70% by the hormone, a reduction comparable to that for ribosomal proteins. The mRNA levels of eIF-4A, eIF-4D, and eIF-2 alpha also were reduced by 60 to 70%, indicating that synthesis rates are proportional to mRNA concentrations. Analysis of polysome profiles showed that the average number of ribosomes per initiation factor polysome was only slightly reduced by dexamethasone, and little or no mRNA was present in messenger ribonucleoproteins. The results indicate that initiation factor gene expression is coordinately regulated with ribosomal protein synthesis but is controlled primarily by modulating mRNA levels rather than mRNA efficiency.

Translational initiation factor expression and ribosomal protein gene expression are repressed coordinately but by different mechanisms in murine lymphosarcoma cells treated with glucocorticoids

P1798 murine lymphosarcoma cells cease to proliferate upon exposure to 10(-7) M dexamethasone and exhibit a dramatic inhibition of rRNA and ribosomal protein synthesis (O. Meyuhas, E. Thompson, Jr., and R. P. Perry, Mol. Cell Biol. 7:2691-2699, 1987). These workers demonstrated that ribosomal protein synthesis is regulated primarily at the level of translation, since dexamethasone did not alter mRNA levels but shifted the mRNAs from active polysomes into inactive messenger ribonucleoproteins. We have examined the effects of dexamethasone on the biosynthesis of initiation factor proteins in the same cell line. The relative protein synthesis rates of eIF-4A and eIF-2 alpha were inhibited by about 70% by the hormone, a reduction comparable to that for ribosomal proteins. The mRNA levels of eIF-4A, eIF-4D, and eIF-2 alpha also were reduced by 60 to 70%, indicating that synthesis rates are proportional to mRNA concentrations. Analysis of polysome profiles showed that the average number of ribosomes per initiation factor polysome was only slightly reduced by dexamethasone, and little or no mRNA was present in messenger ribonucleoproteins. The results indicate that initiation factor gene expression is coordinately regulated with ribosomal protein synthesis but is controlled primarily by modulating mRNA levels rather than mRNA efficiency.

Glucocorticoid-receptor complexes are associated with small RNA in vitro

Identification of RNA associated with soluble glucocorticoid-receptor complexes of HeLa cells was performed by immunoprecipitation of receptor complexes with a monoclonal antibody raised against rat liver glucocorticoid receptor. Polyacrylamide gel electrophoresis of RNA extracted from immunoprecipitates of cytosolic complexes revealed the presence of eight RNA bands, consisting of 28S, 18S, and small RNAs, including 5.8S, 5S and tRNA. A comparison of RNA species immunoprecipitated by monoclonal anti-glucocorticoid receptor antibody and IgG purified from normal mouse serum showed that four small RNAs were preferentially recovered after immunoprecipitation with anti-glucocorticoid receptor antibody. When these species were analyzed on sequencing gels, their nucleotide lengths coincided with those of 7-3, 7S, U2, and U1 RNA. Immunoprecipitation of nuclear extracts containing glucocorticoid-receptor-RNA complexes showed that the same set of small RNAs was preferentially immunoprecipitated by anti-glucocorticoid receptor antibody. The four small RNAs we detected represented minor species in whole extracts, and their preferential immunoprecipitation by anti-glucocorticoid receptor antibody was prevented by removal of glucocorticoid-receptor complexes from HeLa cell extracts. We conclude that 7-3, 7S, U2, and U1 RNA are associated with glucocorticoid-receptor complexes in vitro, and hypothesize that post-transcriptional effects of glucocorticoids may in part be mediated through interaction of receptor complexes with these small RNAs.

Glucocorticoid regulation of the rat cytochrome P450c (P450IA1) gene: receptor binding within intron I

The actions of polycyclic aromatic hydrocarbons and glucocorticoids to regulate the expression of cytochrome P450c were investigated using cultured fetal rat hepatocytes. Cytochrome P450c mRNA content, determined by Northern blot analysis, was induced in cells treated with 1,2-benzanthracene from levels undetectable in untreated cells. When dexamethasone was included in the culture medium together with 1,2-benzanthracene there was a further 2-fold increase in the induction of cytochrome P450c mRNA. The concentration of dexamethasone required for a half-maximal increase in cytochrome P450c mRNA content was approximately 10(-9) M. By nuclear run-on transcription assays, treatment with 1,2-benzanthracene induced cytochrome P450c transcription 5.3-fold over untreated cells. In the presence of dexamethasone and 1,2-benzanthracene, there was a further 2-fold increase in cytochrome P450c transcription. Southwestern blotting and exonuclease footprinting methods have identified binding interactions of a purified glucocorticoid receptor fraction with portions of the cytochrome P450c gene within the first intron. Using a chimeric plasmid containing the first intron, the first exon, and 824 bp of 5'-flanking region of the cytochrome P450c gene, chloramphenicol acetyltransferase activity was induced in transfected HepG2 hepatoma cells by the addition of 1,2-benzanthracene. The addition of dexamethasone induced a further 2.2-fold increase in activity. Deletion of the first intron within the chimeric plasmid abolished responsiveness to dexamethasone. It is concluded that glucocorticoids act together with polycyclic aromatic hydrocarbons to increase the levels of cytochrome P450c expressed in the fetal rat hepatocyte, and that this action is mediated by the glucocorticoid receptor. A glucocorticoid responsive element, which binds the glucocorticoid receptor, has been identified within the first intron of the cytochrome P450c gene. These results suggest that glucocorticoids play a significant role in the response of the hepatic cytochrome P450c gene to xenobiotics.

Monocyte C1-inhibitor synthesis in patients with C1-inhibitor deficiency

Monocytes of seven out of eight patients with type 1 C1-inhibitor (C1-inh) deficiency (HAE) produced 40% as much C1-inh as monocytes from normal donors (controls). In contrast, monocytes from three patients with type 2 and three patients with acquired C1-inh deficiency produced similar amounts of C1-inh as controls. Recombinant gamma-interferon (gamma-interferon 10 ng/ml) stimulated C1-inh production of C1-inh (eight-10-fold) by control and patients' monocytes. Monocytes from patients with type 1 HAE contained 40% the level of C1-inh messenger ribonucleic acid (mRNA) found in control monocytes. Gamma-interferon increased the abundance of C1-inh mRNA by the same extent in both control and patients' monocytes. C1-inh protein and mRNA were undetectable in the monocytes of one patient, unless stimulated by gamma-interferon. Under these conditions, his monocytes produced comparable amounts of C1-inh (protein and mRNA) as gamma-interferon-stimulated monocytes of the other type 1 HAE patients. The data suggest that in most type 2 HAE patients there is a lesion in the C1-inh gene such that mRNA is transcribed by a single allele.

Small cytoplasmic RNA associated with polyadenylated RNA is involved in the hormonal regulation of gene expression

The fraction of small RNA (sacc-RNA) associated with cytoplasmic rat liver poly(A)+ RNA by non-covalent, possibly complementary, interactions has been isolated and studied. Fingerprint analysis and Northern blot hybridization data reveal that the specific changes occur in the population of sacc-RNA in response to glucocorticoid treatment. The close similarity of the oligonucleotide composition of sacc-RNA and RNA-component of small nuclear RNP-acceptor of glucocorticoid hormones has been found. The hypothesis of the involvement of the small RNA in the hormonal regulation of posttranscriptional stages of gene expression in the cytoplasm has been put forward.

Concomitant transcriptional and post-transcriptional control of mRNA abundance during human myeloid cell differentiation

The mechanisms controlling the expression of two genes during the differentiation of HL60 cells have been studied. The relative abundance of one mRNA, designated 2B5, increases during retinoic acid-induced differentiation; this increase can be accounted for, in part at least, by a marked increase in the rate of transcription of the gene. The relative abundance of the second, pCG56, decreases during retinoic acid-induced differentiation although the rate of transcription of this gene also increases during the course of differentiation. The bulk of pCG56 transcripts, though polyadenylated and apparently fully processed, are located in the nuclei of the uninduced cells, but on the polysomes of the induced cells. The data indicate that the change in the expression of the gene encoding pCG56 RNA is regulated differently from that encoding 2B5 RNA, and are interpreted as evidence that the pCG56 gene is regulated by an interaction between transcriptional and post-transcriptional controls. Furthermore, the latter includes both mRNA stability and a post-transcriptional mechanism that has not previously been demonstrated in differentiating cells, viz. nucleo-cytoplasmic transport of mRNA.

Molecular cloning of gene sequences regulated during squamous differentiation of tracheal epithelial cells and controlled by retinoic acid

A cDNA library was constructed from polyadenylated RNA present in squamous differentiated rabbit tracheal epithelial cells. Screening of the cDNA library was aimed at identifying RNAs that were abundant in squamous cells and expressed at low levels in undifferentiated cells. Two different recombinants were obtained containing inserts, 0.86 and 0.77 kilobases (kb) in size, that hybridized to mRNAs 1.0 and 1.25 kb in length. These RNAs were present at approximately 50-fold higher levels in squamous cells than in proliferative or confluent retinoic acid-treated cells. The increase in the levels of the 1.0- and 1.25-kb RNAs correlated closely with the onset of squamous differentiation and was not related to induction of terminal cell division. Treatment of rabbit tracheal epithelial cells with transforming growth factor beta, which induces squamous differentiation in these cells, also resulted in elevated levels of the 1.0- and 1.25-kb RNAs. The increased levels of these RNAs in squamous cells appeared to a large extent to be regulated at a posttranscriptional level. Retinoic acid not only inhibited the increase in the levels of the 1.0- and 1.25-kb RNAs but also reversed the expression of these RNAs in squamous cells. These results suggest that retinoic acid affects, directly or indirectly, molecular events that induce alterations in the posttranscriptional processing of the transcripts corresponding to the 1.0- and 1.25-kb RNAs.

Glucocorticoid regulation of insulin receptor gene transcription in IM-9 cultured lymphocytes

We have reported that glucocorticoids increase steady state insulin receptor mRNA levels in target cells. In the present study using IM-9 cultured human lymphocytes, we investigated the mechanism responsible for this glucocorticoid mediated increase in insulin receptor mRNA levels. Incubation of IM-9 cells with 100 nM dexamethasone for 4 h stimulated a parallel increase in both polysomal and nuclear insulin receptor RNAs indicating that glucocorticoids did not alter the nuclear transport of insulin receptor RNA. Dexamethasone did not alter insulin receptor mRNA half life (t 1/2 = 140 +/- 20 min), indicating that glucocorticoids did not influence mRNA stability. Furthermore, the dexamethasone-induced increase in insulin receptor mRNA levels was not blocked by pretreatment of cells with cycloheximide indicating that the glucocorticoid effect was independent of new protein synthesis. When the labeled transcripts from nuclear run-off incubations were then hybridized to immobilize human insulin receptor cDNA, a three- to fourfold increase in transcriptional activity was observed. This transcriptional effect occurred before the increase in steady state insulin receptor mRNA levels and over the same range of dexamethasone concentrations. These studies indicate therefore a direct effect of glucocorticoids on insulin receptor gene transcription, and demonstrate that the insulin receptor gene is under hormonal control.

Glucocorticoid receptor binding to defined regions of alpha 2u-globulin genes

A DNA-cellulose competition assay was used to study binding of glucocorticoid receptor complexes to two alpha 2u-globulin genes, RAP 01 and RAO 01. Two binding regions were found in RAP 01, one localized between bp -642 and -452, the other between -252 and -118 from the transcriptional initiation site. Only the second region was found in RAO 01. The binding affinity was comparable to that observed using a long terminal repeat fragment of mouse mammary tumor virus. Both regions contain sequences homologous to a 17-bp consensus proposed for the glucocorticoid receptor binding. Therefore, despite evidence that glucocorticoid induction of alpha 2u-globulin may be indirect, a direct action of the receptor in the 5'-upstream region of the genes cannot be excluded.

Plasminogen activator inhibitor type 1 biosynthesis and mRNA level are increased by dexamethasone in human fibrosarcoma cells

Dexamethasone increases type 1 plasminogen activator inhibitor (PAI-1) activity released from the human fibrosarcoma cell line HT-1080. We demonstrated that dexamethasone caused about 10-fold increases in the intracellular and extracellular levels of PAI-1 protein, as measured by an enzyme-linked immunosorbent assay, in the rate of PAI-1 biosynthesis, and in the PAI-1 mRNA level. The effects on PAI-1 biosynthesis and mRNA level were detectable within 4 h and were maximal 16 to 24 h after the addition of dexamethasone. Cycloheximide did not inhibit the dexamethasone-induced increases in the capacity of the cells to synthesize PAI-1 and in the PAI-1 mRNA level.

Changing patterns of transcriptional and post-transcriptional control of liver-specific gene expression during rat development

Genes coding for unique or tissue-specific (differentiated) functions in the liver are induced at different times during development. It has generally been felt that transcriptional control represents the dominant mechanism for regulating expression of these genes. We have determined the relative transcription rates and mRNA steady-state levels for a series of genes specifically or preferentially expressed in rat liver and find examples of transcriptional control (albumin, alpha-fetoprotein, alpha 1-antitrypsin, tyrosine aminotransferase, transferrin, and cytochrome P450, TF-1) and post-transcriptional control (alpha 1-acid glycoprotein, apolipoproteins A-1 and E, malic enzyme, and ATP citrate lyase), as well as "mixed" regulation (ligandin and cytochrome P450, R17). Examples have been identified in which the predominant mode for regulating expression of preferentially expressed genes changes from transcriptional to post-transcriptional at different stages of liver development and some members of multigene families (cytochrome P450s and apolipoprotein genes) also show independent and sometimes contrasting modes of regulation. Therefore, it appears that regulation of specific gene expression in the liver is a dynamic process, far more complex than heretofore suspected, and a much greater contribution of post-transcriptional regulation accounts for changes in expression of genes representing major functions of the liver.

Molecular cloning of gene sequences regulated during squamous differentiation of tracheal epithelial cells and controlled by retinoic acid

A cDNA library was constructed from polyadenylated RNA present in squamous differentiated rabbit tracheal epithelial cells. Screening of the cDNA library was aimed at identifying RNAs that were abundant in squamous cells and expressed at low levels in undifferentiated cells. Two different recombinants were obtained containing inserts, 0.86 and 0.77 kilobases (kb) in size, that hybridized to mRNAs 1.0 and 1.25 kb in length. These RNAs were present at approximately 50-fold higher levels in squamous cells than in proliferative or confluent retinoic acid-treated cells. The increase in the levels of the 1.0- and 1.25-kb RNAs correlated closely with the onset of squamous differentiation and was not related to induction of terminal cell division. Treatment of rabbit tracheal epithelial cells with transforming growth factor beta, which induces squamous differentiation in these cells, also resulted in elevated levels of the 1.0- and 1.25-kb RNAs. The increased levels of these RNAs in squamous cells appeared to a large extent to be regulated at a posttranscriptional level. Retinoic acid not only inhibited the increase in the levels of the 1.0- and 1.25-kb RNAs but also reversed the expression of these RNAs in squamous cells. These results suggest that retinoic acid affects, directly or indirectly, molecular events that induce alterations in the posttranscriptional processing of the transcripts corresponding to the 1.0- and 1.25-kb RNAs.

Plasminogen activator inhibitor type 1 biosynthesis and mRNA level are increased by dexamethasone in human fibrosarcoma cells

Dexamethasone increases type 1 plasminogen activator inhibitor (PAI-1) activity released from the human fibrosarcoma cell line HT-1080. We demonstrated that dexamethasone caused about 10-fold increases in the intracellular and extracellular levels of PAI-1 protein, as measured by an enzyme-linked immunosorbent assay, in the rate of PAI-1 biosynthesis, and in the PAI-1 mRNA level. The effects on PAI-1 biosynthesis and mRNA level were detectable within 4 h and were maximal 16 to 24 h after the addition of dexamethasone. Cycloheximide did not inhibit the dexamethasone-induced increases in the capacity of the cells to synthesize PAI-1 and in the PAI-1 mRNA level.

Regulation of albumin synthesis by hormones and amino acids in primary cultures of rat hepatocytes

Culture conditions necessary for optimizing albumin secretion were studied in rat hepatocytes maintained in a chemically defined, serum-free medium. Amino acid analysis of the culture medium, which was based on a 1:1 mixture of Ham's F12:Dulbecco's modified Eagle's medium (unsupplemented medium), revealed that certain essential amino acids were depleted from this medium over a 24-h incubation. Rates of albumin secretion were significantly higher and better maintained when the medium was supplemented with additional amino acids (supplemented medium). Moreover, selective removal of an essential amino acid resulted in an immediate decrease in total protein and albumin synthesis and after 48 h a further selective decrease in albumin synthesis. Linear rates of albumin secretion were observed over a wide variety of experimental conditions, but secretion was not strictly proportional to cell number. Maximal rates of secretion were obtained at plating densities of 2-3 X 10(6) cells/60 mm culture dish. Albumin secretion also increased with time in culture reaching a maximum on days 3 and 4. When added singly, either insulin or dexamethasone increased rates of albumin secretion in a dose-dependent manner, but both hormones and an adequate supply of amino acids were necessary for maximal rates of secretion as well as long-term maintenance of the hepatocytes (greater than 3-4 days). In the presence of dexamethasone the dose-response curve for insulin was shifted toward physiological insulin concentrations. Changes in rates of albumin secretion in response to added hormones in supplemented media were found to parallel changes in albumin synthesis and relative amounts of albumin mRNA. Changes in gene transcription were probably involved.

Effects of bovine pancreatic ribonuclease A, S protein, and S peptide on activation of purified rat hepatic glucocorticoid-receptor complexes

Bovine pancreatic ribonuclease (RNase) A and S protein (enzymatically inactive proteolytic fragment of RNase A which contains RNA binding site) stimulate the activation, as evidenced by increasing DNA-cellulose binding, of highly purified rat hepatic glucocorticoid-receptor complexes. These effects are dose dependent with maximal stimulation of DNA-cellulose binding being detected at approximately 500 micrograms (50 units of RNase A/mL). RNase A and S protein do not enhance DNA-cellulose binding via their ability to interact directly with DNA or to increase nonspecific binding of receptors to cellulose. Neither S peptide (enzymatically inactive proteolytic fragment which lacks RNA binding site) nor cytochrome c, a nonspecific basic DNA binding protein, mimics these effects. RNase A and S protein do not stimulate the conformational change which is associated with activation and is reflected in a shift in the elution profile of receptor complexes from DEAE-cellulose. In contrast, these two proteins interact with previously heat-activated receptor complexes to further enhance their DNA-cellulose binding capacity and thus mimic the effects of an endogenous heat-stable cytoplasmic protein(s) which also function(s) during step 2 of in vitro activation [Schmidt, T. J., Miller-Diener, A., Webb, M. L., & Litwack, G. (1985) J. Biol. Chem. 260, 16255-16262]. Preadsorption of RNase A and S protein to an RNase affinity resin containing an inhibitory RNA analogue, or trypsin digestion of the RNA binding site within S protein, eliminates the subsequent ability of these two proteins to stimulate DNA-cellulose binding of the purified receptors.(ABSTRACT TRUNCATED AT 250 WORDS)