Glucocorticoid induction of hepatic alpha2u-globulin synthesis and messenger RNA level in castrated male rats in vivo

Down-regulation of alpha-2u globulin in renal mitochondria of STZ-induced diabetic rats observed by a proteomic method

AIM

To identify the changes of mitochondrial protein expression in diabetic renal parenchyma and to characterize their molecular functions and biological processes in diabetes.

METHODS

Mitochondrial proteins extracted from renal parenchyma mitochondria of streptozotocin-induced diabetic rats and normal rats were separated by two-dimensional polyacrylamide gel electrophoresis and identified by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry.

RESULTS

Eleven proteins from 533 visualized protein spots displayed significant different expressions in mitochondria of diabetic kidneys compared with those in normal ones. Among these altered proteins, two proteins with the most obvious changes in protein expression were identified as alpha-2u globulin (mature protein, named A2) and its proteolytically modified form (named A2-fragment) respectively. These proteins were found in mitochondria of male rat renal parenchyma and were proved to be down-regulated in diabetic rats simultaneously.

CONCLUSION

Our results suggest that down-regulation of alpha-2u globulin may be associated with an abnormal β-oxidation of long-chain fatty acids during diabetes. The decreased expression of A2-fragment in renal mitochondria of diabetic nephropathy may reduce fatty acid β-oxidation, which leads to a diminished energy supply from mitochondria to kidney tissue and the deposition of a large number of fatty acids in the kidney, ultimately causing and aggravating kidney damage. In conclusion, these findings may be helpful for understanding the molecular mechanism of diabetic nephropathy.

Modeling of corticosteroid pharmacogenomics in rat liver using gene microarrays

Corticosteroid (CS) pharmacogenomics was studied using gene microarrays in rat liver. Methylprednisolone (MPL) was administered intravenously at 50 mg/kg. Rats were sacrificed and liver excised at 17 time points over 72 h. RNAs from individual livers were used to query Affymetrix GeneChips that contain sequences for 8000 genes. Cluster analysis revealed six temporal patterns consisting of 197 CS-responsive probes representing 143 genes. Based on our fifth-generation model of CS pharmacokinetics/pharmacodynamics (PK/PD), mechanistic models were developed to describe the time pattern for each CS-responsive gene. Two clusters showed increased expression with different effect duration. PK/PD models assuming CS stimulation of mRNA synthesis were applied. Another two clusters showed an initial decline followed by delayed increase, suggesting two mechanisms might be involved jointly. The initial suppression was captured by CS inhibition of mRNA synthesis or stimulation of degradation. CS may also stimulate the production of a biosignal (transcription factors or other hormones), which can cause secondary induction of the target mRNA. One cluster showed a very abrupt increase in message followed by rapid decrease. These genes were lymphocytic in origin and were modeled combining the fast gene induction effect of CS in lymphoid cells and its direct lymphocyte trafficking effect. Another cluster showed reduction persisting for 18 h, which was described by CS inhibition of mRNA synthesis. Our results reveal the marked diversity of genes regulated by CS via a limited array of mechanisms. These PK/PD models provide quantitation of CS pharmacogenomics and new hypotheses regarding understanding of diverse mechanisms of CS receptor-gene mediated action.

Hepatic alpha(2u)-globulin mRNA levels and diethylstilbestrol-associated testicular atrophy in rats

Biosynthesis of alpha(2u)-Globulin (alpha(2u)-g) is under multihormonal regulation. In this study, we investigated histopathologic changes in the testis and hepatic alpha(2u)-g messenger ribonucleic acid (mRNA) levels in male rats after administration of the potent estrogen diethylstilbestrol (DES) at 0. 01, 0.1, or 1 mg/kg/day by gavage for 14 days. DES treatment decreased hepatic alpha(2u)-g mRNA levels in a dose-dependent manner accompanied by atrophic histopathologic changes in the testis. In addition, alpha(2u)-g mRNA levels were lowest in animals with the most marked testicular changes. Hepatic alpha(2u)-g mRNA may be a useful biomarker for the evaluation of endocrine disruption in male rats.

Molecular evidence of complex tissue- and sex-specific mRNA expression of the rat alpha(2u)-globulin multigene family

alpha(2u)-Globulin is well known to be a rat protein encoded by a highly homologous multigene family with more than twenty members. We report here the cloning and identification of major alpha(2u)-globulin mRNA species expressed in various tissues. Initially, eight individual clones (PGCL1-8) were obtained from a male preputial gland cDNA library. Data base analysis with BLAST demonstrated six mRNAs to be novel, all clones being characterized by highly conserved sequence motifs as lipocalins. All cDNAs contained an open reading frame of 543 nucleotides and encode 181 amino acid proteins showing 92.5-98.7% and 87.3-98.3% nucleic and amino acid identity, respectively. Denaturing gradient gel electrophoresis (DGGE) with sequence analysis showed that PGCL4 is a major member in the female mammary gland, and in the submaxillary and lachrymal glands of both sexes, while the counterpart in male liver and the coagulate glands was found to be PGCL1. Numbers of cDNA species including PGCL1 and PGCL4 were found in preputial glands, no sex-related difference being observed. These results directly demonstrate complex tissue- and sex-specific expression of alpha(2u)-globulins in terms of mRNA species, providing useful information for understanding regulation of the alpha(2u)-globulin multigene family.

A physiological model for ligand-induced accumulation of alpha 2u globulin in male rat kidney: roles of protein synthesis and lysosomal degradation in the renal dosimetry of 2,4,4-trimethyl-2-pentanol

A physiologically based pharmacokinetic (PBPK) model was constructed for the disposition of 2,4,4-trimethyl-2-pentanol (TMP-2-OH) in male rats and its induction of accumulation of renal alpha2u-globulin (alpha2u). The model included diffusion-restricted delivery of TMP-2-OH to compartments representing liver, lung, fat, kidney, GI tract, aggregated rapidly perfused tissues, and aggregated slowly perfused tissues. Metabolism by oxidation and glucuronidation was included for liver and kidneys. Rates of hepatic alpha2u production and resorption by renal proximal tubules were taken from the literature. Degradation of liganded alpha2u by renal lysosomal cathepsins was modeled with a Km value corresponding to the measured 30% reduction in proteolytic efficiency and with free and bound forms of alpha2u competing for access to the enzymes. Increased pinocytotic uptake of alpha2u into the kidney induces cathepsin activity. A model that ascribed renal alpha2u accumulation solely to reduced lysosomal proteolysis failed to reproduce the observed accumulation. The model could reproduce experimental observations if a transient increase in hepatic synthesis of alpha2u, stimulated by the presence of liganded alpha2u in the blood, and accelerated secretion of the protein from the liver were assumed. This model reproduces time course data of blood and kidney TMP-2-OH and renal alpha2u concentrations, suggesting that renal accumulation of alpha2u is not simply a consequence of reduced proteolytic degradation but may also involve a transient increase in hepatic alpha2u production. The model predicts increased delivery of TMP-2-OH to the kidney and consequent increased renal production of potentially toxic TMP-2-OH metabolites than would be the case if no alpha2u were present. Induced lysosomal activity and increased production of toxic metabolites may both contribute to the nephrotoxicity observed in male rats exposed to an alpha2u ligand or its precursor.

Differential regulation of the cytochrome P450 3A1 gene transcription by dexamethasone in immature and adult rat liver

We have previously shown that the in vivo induction of cytochrome P450 3A1 by dexamethasone occurs through a sharp and early transcriptional activation in the immature rat liver that is drastically impaired in adults [Telhada, M. B., Pereira, T. M. & Lechner, M. C. (1992) Arch. Biochem. Biophys. 298, 714-725]. In the present study we investigate the relative importance of cytochrome P450 3A1 gene transcription on the adaptive response to the synthetic glucocorticoid dexamethasone, by measuring the time-course run-on transcription rate and concomitant mRNA accumulation in the male rat liver at two different ontological developmental stages. The primary (direct) or secondary (dependent on protein neo-synthesis) nature of the in vivo inductive response to dexamethasone and to pregnenolone 16 alpha-carbonitrile, is further investigated by inhibiting translation by cycloheximide pretreatment. The induction of cytochrome P450 3A1 gene transcription by the anti-glucocorticoid pregnenolone 16 alpha-carbonitrile is demonstrated to occur through a secondary mechanism, requiring ongoing protein biosynthesis, regardless of the developmental stage of the animals. Conversely, a significant developmentally controlled change is observed in the inductive response of the cytochrome P450 3A1 gene to dexamethasone, characterized by a markedly delayed transcriptional activation in the adult rat liver (90 day old) as compared to the immature rat liver (21 day old). This is consistent with the net primary response of the cytochrome P450 3A1 gene to dexamethasone demonstrated in this study to occur in the immature rat liver and almost lost at the adult stage, when protein neo-synthesis becomes essential for the inductive response. Our results demonstrate (a) a difference in the mechanisms underlying induction of the cytochrome P450 3A1 gene by the glucocorticoid agonist dexamethasone and by the antagonist pregnenolone 16 alpha-carbonitrile, and (b) an important change in the mechanisms of the inductive response to dexamethasone, associated with the immature/adult liver phenotype transition. This indicates the participation of specific labile transcription factors in the induction of cytochrome P450 3A1 gene by the synthetic glucocorticoids.

The role of lysosomes in hyaline droplet nephropathy induced by a variety of pharmacological agents in the male rat

The male rat is prone to hyaline droplet formation in renal proximal tubular cells. Several unrelated pharmaceutical agents exacerbate the formation and accumulation of these droplets. Where the loading of the proximal tubular cells is marked it gives rise to increased cell turnover and a hyaline droplet nephropathy develops. Cytochemical procedures, have confirmed that this accumulation of hyaline droplets represents an increase in the size and number of secondary lysosomes involved in protein uptake and metabolism. This predisposition of the male rat to develop hyaline droplet nephropathy relates to (1) the large amounts of the low-molecular-weight protein alpha 2U globulin in the glomerular filtrate, (2) the resistance of the globulin to proteolysis, and (3) the low protease activity in the proximal tubule lysosomes. The current data would suggest that the pharmacological agents, which cause the nephropathy, exert their effect by reducing the proteolytic breakdown of alpha 2U globulin in the proximal tubule lysosomes. This results in the overloading of a system which is already operating near maximal load. Female rats, and all other species excrete only small amounts of alpha 2U globulin or similar proteins, which are more easily hydrolyzed. Thus it is argued that the type of hyaline droplet nephropathy induced by these pharmacological agents is unique to the male rat and of little relevance to man.

Content of glucocorticoid receptor and arginase in gastric cancer and normal gastric mucosal tissues

The content of glucocorticoid receptor (GR) and arginase in human gastric cancer and the corresponding normal gastric mucosal tissues was determined. Among the 25 patients studied, the GR content in gastric cancer tissues was 33.2 +/- 10.2 fmol/mg protein versus 7.6 +/- 3.4 fmol/mg protein in gastric mucosal tissues. This difference is statistically significant (P less than 0.005). Of the 25 paired samples, 19 cancer tissues contained GR, whereas only seven of the normal mucosal tissues had GR. The level of arginase in gastric cancer tissues in 19 patients was assayed, it was 26.6 +/- 4.2 ng/mg protein which is also significantly higher than that in normal gastric mucosal tissues (13.5 +/- 1.8 ng/mg protein) (P less than 0.005). Since glucocorticoids and arginase are potent immune suppressive agents, the increased level of GR and arginase in gastric cancer tissue suggest that these glucocorticoid-related factors in gastric cancer tissue may play a partial role in regulating cellular immunity.

Regulation of alpha 1-acid glycoprotein plasma concentration by sex steroids and adrenal-cortical hormones during experimental inflammation in the rat

Treatment of adult intact rats with sex steroids (estradiol-17 beta, ethynylestradiol, dihydrotestosterone) raises the concentration of serum acute-phase alpha 1-acid glycoprotein (AGP). Estrogens are more effective than dexamethasone, and experimental inflammation causes an additive effect on AGP synthesis when ethynylestradiol is given simultaneously. Adrenaline is also able to increase the AGP level. Experiments with adrenalectomized and adrenalectomized plus castrated rats result in a 50% reduction in the serum level of AGP as compared with that in normal and hypophysectomized rats. Although ethynylestradiol is the strongest inducer of AGP synthesis in intact animals, it is unable to enhance significantly the AGP level in adrenalectomized rats, contrary to dexamethasone. Adrenalectomized rats are incapable of undergoing a substantial increase in plasma AGP level following experimental inflammation, and ethynylestradiol or adrenaline cannot take the place of dexamethasone in inducing high levels of AGP in these inflamed rats. These results indicate that glucocorticoids play an obligatory role in modulating AGP synthesis either by directly regulating the AGP gene or in modulating AGP synthesis by increasing the stability of AGP mRNA. Finally, it is suggested that glucocorticoids may also act in unmasking receptor binding sites at the AGP gene level for other mediators such as sex steroids and putative inflammatory factors.

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.

Sex dimorphism and hormonal regulation of rat tissue kallikrein mRNA

The regulation of rat tissue kallikrein mRNA levels was investigated by RNA filter hybridization using a kallikrein cDNA probe and by in vitro translation of isolated RNA. The synthesis of a 37 kDa polypeptide has been hybrid-arrested by the tissue kallikrein cDNA in cell-free translation assays directed by submandibular mRNA and the quantitation of this protein was used as a measure of translational activity of kallikrein mRNA. In Northern blot analyses, relative kallikrein mRNA levels were found to be 60-fold higher in submandibular gland than in pancreas and 20-fold higher than in kidney. In addition, it was noted that kallikrein mRNA is differentially regulated in tissues from male and female animals. Rat submandibular gland kallikrein mRNA is 2-times more abundant in male animals as in females. This trend is reversed in kidney, where the kallikrein mRNA in females is twice that in male animals. Relative submandibular gland kallikrein mRNA levels were found to be responsive to hormonal manipulation as measured by both Northern blotting and cell-free translation assays. Castration of male animals resulted in a decrease of kallikrein mRNA which could be partially restored by treatment with thyroxine and almost completely restored by testosterone treatment. The submandibular gland kallikrein mRNA in normal female rats was increased up to 30% by administration of testosterone or thyroxine. Adrenalectomized female rats showed a decrease in submandibular kallikrein mRNA which was significantly increased by testosterone, thyroxine, aldosterone and cortisol, with the largest effect being a 2- to 2.4-fold increase in cortisol-treated rats. These results indicate that hormones regulate tissue kallikrein synthesis in the rat submandibular gland, at least in part, by altering kallikrein mRNA accumulation.

Influence of neonatal androgenization on the expression of alpha 2u-globulin in rat liver and submaxillary gland

We studied the influence of neonatal androgenization on the serum level of alpha 2u-globulin, the level of the corresponding mRNA in liver and submaxillary gland and the concentration of an androgen and oestrogen binding protein in liver cytosol. Male rats gonadectomized on day 15 (after the neonatal surge of androgen secretion) were used as neonatally androgenized animals, their female littermates gonadectomized at the same age served as controls. Using a sensitive radioimmunoassay it could be demonstrated that only very low levels of alpha 2u-globulin are present in adult female control animals. Neonatal androgenization increases these levels some 14-fold. Stimulation with testosterone or dexamethasone results in a relative increase in the serum levels in animals of both sexes. After 11 days of treatment with testosterone propionate or dexamethasone, however, the final alpha 2u-globulin levels are respectively 1.8 times and 8 times higher in neonatally androgenized rats as compared to their female littermates. The concentration of the androgen and oestrogen binding protein in rat liver cytosol displays parallel sex differences in unstimulated animals and parallel changes after treatment with androgens and glucocorticoids. Measurements of alpha 2u-globulin mRNA by dot blot hybridization and by translation in reticulocyte lysate show a good correlation between the serum levels of alpha 2u-globulin and the corresponding mRNA in the liver. The abundance of alpha 2u-globulin mRNA in submaxillary gland is not influenced by neonatal androgens or hormone treatment during adulthood. These data suggest that neonatal androgenization directly or indirectly influences the availability for transcription and/or the transcription rate of alpha 2u-globulin genes in the liver.

Alterations in the activities of subcellular fractions marker enzymes in rat liver and brain by hydrocortisone and corticosterone treatment

The effect of subcutaneous injection of hydrocortisone and corticosterone on the activity values of some subcellular fractions marker enzymes from rat liver and brain was investigated and compared with controls (without treatment with hormones). The following enzymes were studied (subcellular fraction are shown between parentheses): N-acetyl-beta-D-glucosaminidase and beta-glucuronidase (lysosomes); succinate dehydrogenase = SDH (mitochondria); glucose-6-phosphatase (endoplasmic reticulum); 5'-nucleotidase and Na+-K+-Mg2+ ATPase (plasma membrane). The specific activity of lysosomal enzymes from liver showed no change when rats were injected either with hydrocortisone or corticosterone. The same enzymes from brain showed significant increases in their activities with both hydrocortisone or corticosterone except beta-glucuronidase; this enzyme gave activity values remaining between the control levels, after treatment with corticosterone. The activity of mitochondrial SDH was increased after corticosterone injection either in liver or brain. After hydrocortisone injection, its activity rises significantly in brain (72%), but it falls in liver compared to the control values. Glucose-6-phosphatase behaves similarly in brain or liver fractions; its activity increases always after corticosterone treatment and decreases by hydrocortisone. The plasma membrane marker enzymes did not change practically in brain fractions, excepted Na+-K+-Mg2+ ATPase which tends to rise its activity after hydrocortisone injection. In liver fractions, both 5'-nucleotidase and Na+-K+-Mg2+ ATPase activities increase either by corticosterone or hydrocortisone treatment, except 5'-nucleotidase which specific activity decreases in liver after hydrocortisone treatment.

Glucocorticoids inhibit the coordinated translation of alpha- and beta-globin mRNAs in Friend erythroleukemia cells

The dimethylsulfoxide (Me2SO)-mediated induction of hemoglobin synthesis in Friend erythroleukemia cells is inhibited by the glucocorticoids hydrocortisone, dexamethasone, and fluocinolone acetonide; hydrocortisone, at concentrations of 10(-5) to 10(-8) M inhibits by 90-30% and fluocinolone acetonide at concentrations of 10(-8) to 10(-11) M shows a greater than 90% inhibition. At these concentrations the hormones have no effect on cell growth or viability. In this study it has been shown that there is a group of proteins, including the alpha- and beta-globins, whose regulation is associated with the induction of Friend erythroleukemia cell differentiation, and that the expression of some of these, in addition to alpha- and beta-globin, is affected by glucocorticoids. The levels of alpha- and beta-globin mRNAs are very close to fully induced levels and preclude transcription as a major site for glucocorticoid control. In addition, it has been shown that glucocorticoids inhibit the translation of alpha- and beta-globin mRNAs, that the level of this inhibition is concentration dependent, and that the translation of beta-globin mRNA is slightly more sensitive to inhibition than the translation of alpha-globin mRNA. It is concluded that, although the translation of alpha- and beta-globin mRNA is a major site of inhibition by glucocorticoids, there is a detectable amount of alpha- and beta-globin synthesized. Thus, part of this mechanism may involve a differential sensitivity of alpha- and beta-globin mRNA translation which results in unequal amounts of globin synthesis and an overall more potent inhibition of hemoglobin formation.

Regulation by glucocorticoids of rat-liver phenylalanine hydroxylase in vivo

Phenylalanine hydroxylase, a liver-associated enzyme, is induced markedly by glucocorticoids in two permanent rat-hepatoma cell lines. In order to gain evidence that this phenomenon also occurs in vivo, we examined the effect of adrenalectomy and/or hormone supplementation on the levels of phenylalanine hydroxylase in the livers of adult rats: glucocorticoid administration increases, and adrenal ablation reduces, the activity of the hepatic enzyme, and the diminution occurring in the latter instance is entirely prevented by concurrent hormone replacement. These results thus corroborate earlier findings from a single experiment and are consistent with the hypothesis that adrenal corticosteroid hormones participate in modulating phenylalanine-hydroxylase levels within the diploid hepatocyte.

Different forms of alpha 2u-globulin in male and female rat urine

alpha 2u-Globulin is usually considered to be present only in male rat urine. This study demonstrates that a very similar protein exists in female rat urine and compares its properties with those of the male form. Isoelectric focusing followed by immunofixation reveals considerable microheterogeneity of alpha 2u-globulin in male and female rat urine. Important sex differences are noted in the banding pattern. The isoelectric point of the major male component (pI approximately equal to 5.3) is considerably higher than that of the major female components (pI approximately equal to 4.6). In addition, the female form of alpha 2u-globulin has a somewhat higher mobility on sodium dodecyl sulphate/polyacrylamide gel electrophoresis than its male counterpart. These sex differences are preserved after purification of alpha 2u-globulin from male and female rat urine by affinity chromatography and enrichment of the major male and female components by ion-exchange chromatography. Immunologically no differences are observed between these purified components and their amino acid composition reveals only minor differences. A slightly higher carbohydrate content is observed in the major female component than in the major male component. Finally evidence is presented that oestrogen treatment suppresses the male forms of alpha 2u-globulin but has no effect on the female forms. The observed differences between the male and female forms and their different hormonal control suggest that they are encoded by different genes.

Tissue-specific control of alpha 2u globulin gene expression: constitutive synthesis in the submaxillary gland

Synthesis of alpha 2u globulin, previously thought to occur only in the male rat liver, has now been demonstrated in the submaxillary salivary gland. Unlike liver, submaxillary synthesis of alpha 2u globulin mRNA is constitutive--that is, independent of the endocrine state, age and sex. Liver and submaxillary alpha 2u globulin mRNAs are of similar size, and their 5' ends map to the same region of the gene. Isoelectric focusing of in vitro translation products revealed that submaxillary mRNA encodes a more acidic subset of alpha 2u globulins than does liver. Salivary alpha 2u globulin mRNA manifests 5% nucleotide divergence, encoding 20 amino acid substitutions, which specifies a more acidic polypeptide than its hepatic counterpart. Thus the liver and submaxillary gland synthesize alpha 2u globulin from different sets of genes that are subject to very different developmental and hormonal control.

Comparative analysis of proteins labelled with [35S]methionine in the liver in vivo and in freshly isolated and short-term-cultured hepatocytes in vitro

[35S]Methionine-labelled liver proteins, analysed by one- or two-dimensional gel electrophoresis showed a strikingly similar pattern whether synthesized in vivo or by freshly isolated hepatocytes. In contrast, major qualitative and quantitative differences were observed with the patterns of labelled proteins found in cultured hepatocytes. The changes detectable very early (within 1 h) in culture affected preferentially the synthesis of cytoskeleton proteins (cytokeratins, actin, myosin), which was dramatically increased. Physical factors like cell attachment appear to be responsible for these changes which, however, occurred more rapidly in the presence of serum. Freshly isolated hepatocytes and short-term-cultured cells responded similarly to insulin and glucagon, which respectively increased and decreased the labelling of the whole set of cellular and exported proteins. Glucocorticoids caused either an increase or a decrease in the labelling of several proteins, but the effects were detectable only under chronic exposure of cultured hepatocytes. Based on these results, freshly isolated hepatocytes appear more representative of the liver in vivo than cultured hepatocytes, and therefore seem more suitable for short-term studies. However, cultured hepatocytes can be used for long-term studies since they maintain many specific liver functions and remain hormonally sensitive.

Multihormonal induction of alpha 2u-globulin in an established rat hepatoma cell line

A subclone of the FU5-5 rat hepatoma cell line has been isolated which is inducible more than several hundred fold for the 20,000 dalton form of the major rat urinary protein alpha 2u-globulin. The basal relative synthetic rate (RSR) in growth medium containing 10% fetal calf serum was less than 2 X 10(-6) of total protein synthesis. Both dexamethasone and insulin were necessary for induction, and yielded a maximum induced RSR of 4-8 X 10(-3). Triiodothyronine (T3), dihydrotestosterone (DHT), rat growth hormone (GH), and estrogen, all of which have been shown to influence the induction of alpha 2u-globulin in the intact rat, were without effect on the cell line. A factor present in fetal calf serum was also necessary for maximum induction, since dexamethasone plus insulin in serum-free medium raised the RSR to only 3 X 10(-5); exogenous T3, GH, and DHT could not substitute for this serum factor. The kinetics of induction by dexamethasone were slow, with a lag of approximately 48 hr followed by a period of increasing RSR for 6-20 days. Removal of dexamethasone from induced cells led to an exponential decline in the RSR (t 1/2 15 hr). The concentrations of dexamethasone and insulin that could yield half maximum induction were 5 X 10(-8)M and 3 X 10(-11)M, respectively. Higher concentrations of insulin, although still in physiological range (10(-9)M), inhibited induction. At yet higher insulin levels, beyond the physiological range, alpha 2u-globulin synthesis returned to maximum values. The lack of DHT, T3, and GH requirement for alpha 2u-globulin induction in this cell line may mean that a regulatory aberrancy has occurred in this transformed cell line, or, alternatively, that these hormones act indirectly in the intact animal. This cell line should prove useful for the study of the molecular events associated with alpha 2u-globulin induction and for genetic approaches to the problem of multihormonal regulation of gene expression.

The role of growth hormone in alpha 2u globulin synthesis: a reexamination

Hypophysectomy of adult male rats abolishes alpha 2u globulin synthesis; synthesis can be fully restored by daily administration of androgen, thyroid hormone, glucocorticoid and growth hormone for 12 days. It has been previously reported that growth hormone is not required to maintain alpha 2u globulin mRNA levels, and that growth hormone functions only translationally. We have reexamined the role of growth hormone in alpha 2u globulin synthesis using a cloned alpha 2u globulin cDNA probe. Measurement of alpha 2u globulin mRNA levels by hybridization and cell-free translation, and of alpha 2u globulin synthesis by pulse-labeling in vivo, demonstrates that growth hormone is required to maintain full, steady state hepatic levels of both alpha 2u globulin and its mRNA. Furthermore, the small amount of hepatic alpha 2u globulin mRNA that accumulates in the absence of growth hormone is efficiently translated in vivo. Thus we now find no evidence for growth-hormone-mediated translational control. We have also found that rats hypophysectomized prepubescently respond to the multihormonal restoration therapy to only 10% of the alpha 2u globulin mRNA levels observed in rats hypophysectomized as adults. This finding suggests that some unidentified pituitary factor(s) is required during puberty to potentiate normal alpha 2u globulin gene expression.

Cloning of alpha 2u globulin cDNA using a high efficiency technique for the cloning of trace messenger RNAs

An extremely high-efficiency technique is described for cloning double-stranded (ds) cDNAs in Escherichia coli. The method, which uses two synthetic oligonucleotide linkers rather than one, results in approx. 200--500 recombinant clones per ng of ds cDNA. This technique was used to clone a cDNA comprising 95% of the full length of the mRNA of alpha 2u globulin, a male rat liver protein, which represents approx. 1% of hepatic messenger RNA. The cloned probe was applied to study the complex hormone controls of alpha 2u globulin mRNA in male and female rats.

Changes in the hepatic levels of messenger ribonucleic acid for malic enzyme during induction by thyroid hormone or diet

Levels of hepatic messenger ribonucleic acid (mRNA) for malic enzyme [L-malate:NADP oxidoreductase (decarboxylating), EC 1.1.1.40] were quantitated in different dietary and hormonal states of the rat. Polysomal or total cellular poly(A)-containing RNA was translated in the rabbit reticulocyte lysate system, which had been treated to reduce endogenous mRNA activity. The relative level of incorporation of radiolabeled amino acid into malic enzyme was determined by immunoprecipitation with antibody to malic enzyme and formaldehyde-fixed Staphylococcus aureus (Cowens I strain) as an immunoadsorbent. The immunoprecipitated product comigrated with purified malic enzyme on sodium dodecyl sulfate--polyacrylamide gel electrophoresis. No malic enzyme was detected when nonspecific antisera or an excess of unlabeled malic enzyme was added during immunoprecipitation. The level of malic enzyme mRNA was found to markedly increase relative to euthyroid, chow-fed rats when the animal was either fed a high carbohydrate, fat-free diet or made hyperthyroid. Animals receiving both treatments had a further increase in mRNA activity to a level which was approximately 0.2% of the total incorporation of [3H]leucine. Levels of malic enzyme activity and the relative rate of synthesis were found to increase roughly in proportion to mRNA levels in these three states. Thus, the induction of malic enzyme by thyroid hormone or high carbohydrate, fat-free diet is due largely to an increase in the mRNA coding for this enzyme.