d-Limonene induced hyaline droplet nephropathy in alpha 2u-globulin transgenic mice

d-Limonene is a hyaline droplet inducing agent and produces nephrotoxicity in male rats when the 1,2-epoxide metabolite binds to alpha 2u-globulin. Mice, which do not synthesize alpha 2u-globulin, are resistant to hyaline droplet nephropathy. In this study, the ability of d-limonene to cause hyaline droplet nephropathy in a transgenic mouse engineered to express alpha 2u-globulin was evaluated. The C57BL/6-derived mice excreted 0.4 +/- 0.1 mg alpha 2u-globulin/day, or approximately 16 mg alpha 2u-globulin/kg body wt. This represents about 30% of the amount excreted by adult male rats (11.9 +/- 1.1 mg/day or approximately 48 mg/kg). Transgenic mice excreted less mouse urinary protein (9.3 +/- 1.2 mg/day) than normal mice (15.1 +/- 1.6 mg/day). Unlike normal male rats, untreated transgenic mice did not show significant spontaneous hyaline droplet formation. Liver microsomes from naive transgenic mice oxidized d-limonene to the cis- and transisomers of the 1,2-epoxide, and following oral treatment with [14C]d-limonene reversible binding of d-limonene equivalents to renal cytosolic proteins was observed. Furthermore, with d-limonene treatment, hyaline droplets were observed in the transgenic mouse kidneys. These droplets, however, were much smaller in size than those seen in d-limonene-treated male rats. The accumulation of alpha 2u-globulin in the kidneys of transgenic mice and normal male rats before and after d-limonene treatment was analyzed by Western blotting. These results indicated that alpha 2u-globulin was present in the kidneys of the control transgenic mice, despite the lack of spontaneous hyaline droplet formation. After d-limonene treatment, approximately a three-fold increase in alpha 2u-globulin in the transgenic mouse kidney was observed, a response similar in magnitude to that seen in d-limonene-treated male rats. These results indicate that expression of alpha 2u-globulin in a species that does not normally develop hyaline droplet nephropathy is necessary and sufficient to render that species sensitive to this renal toxicity.

Selective interferon-alpha/beta effects on platelet-derived growth factor-stimulated processes in quiescent BALB/c-3T3 fibroblasts

Interferon-alpha/beta (IFN-alpha/beta) suppresses cell cycle activation by platelet-derived growth factor (PDGF) as well as the induction of the 31-kD (pI) and the 35-kD (pII) proteins in density-arrested BALB/c-3T3 cells. We report that elevation of [Ca2+]i by ionomycin induces the synthesis of the 31-kD protein, but not that of the 35-kD protein. Since IFN blocks the PDGF-induced elevation of [Ca2+]i, these results suggest that IFN treatment may suppress pI induction by impairing this PDGF-activated signal transduction pathway. In contrast, because ionomycin did not induce the 35-kD protein, the suppression by IFN of PDGF-induced pII appears to be mediated via a pathway distinct from that operating in the suppression of pI. In BALB/c-3T3 cells, IFN-alpha/beta did not itself affect the turnover or de novo synthesis of inositol phospholipids and the cellular content of diacylglycerol, nor did IFN block the enhancement of these parameters by PDGF.

Post-translational processing of the inter-alpha-trypsin inhibitor in the human hepatoma HepG2 cell line

In human hepatoma HepG2 cells, the serum inter-alpha-trypsin inhibitor (ITI)-like protein is synthesized from two protein precursors, the heavy chain (H) H2 and the light chain (L). Both of them carry sulphate groups involved in the chondroitin sulphate glycosaminoglycan (GAG) linkage, as demonstrated by [35S]sulphate labelling, chondroitinase digestion and inhibition with beta-D-xyloside, an artificial GAG acceptor. While inhibition of N-glycosylation prevented neither the maturation nor the secretion of the ITI-related entities, brefeldin A induced the accumulation of H and L precursors in the cells, therefore blocking subsequent association and maturation of the precursors before their secretion. The enzyme system involved in the ester linkage between H and L chains is localized in the trans-Golgi network since no ITI-like protein could be obtained in the presence of monensin; instead free heavy-chain protein forms and bikunin were secreted in culture supernatants. The ITI-like protein synthesized by HepG2 cells is therefore composed of two heavy chains HC2 linked to two bikunin chains by chondroitin sulphate bridges, although the GAG linkage between HC2 chains is presumably different. Further, a different maturation route leading to restricted heavy-chain forms, Hm and Hd, could be shown.

Cell proliferation and renal carcinogenesis

Enhanced cell proliferation occurs at several stages of renal tumorigenesis. Initiation by genotoxic nephrocarcinogens such as dimethylnitrosamine (DMN) is likely a result of DNA damage coupled with an initial burst of DNA synthesis associated with the cytotoxic effects of the compound. The level of initiation by DMN can be further enhanced by unilateral nephrectomy or hydronephrosis, which induces a brief burst of cell proliferation followed by tumorigenesis in the contralateral kidney. The role of sustained cell proliferation in renal tumor development is less well understood. The most compelling evidence comes from studies with nongenotoxic renal carcinogens such as unleaded gasoline and d-limonene, which induce alpha 2u-globulin (alpha G) nephropathy and renal epithelial tumors exclusively in male rats. Sustained increases in cell proliferation in these studies depend on the presence of a chemical-alpha G complex in phagolysosomes of P2 proximal tubule cells, which results in cytotoxicity and compensatory hyperplasia only in male F344 rats, but not female F344 rats or alpha G deficient male NBR rats. Furthermore, initiation-promotion experiments demonstrated a strong correlation between the dose-response of cell proliferation and the incidence of preneoplastic and neoplastic lesions. Clearly, similar correlative studies with a number of other renal carcinogens and non-carcinogens are warranted before general conclusions can be made. Cell proliferation is excessively elevated in tubules affected by chronic progressive nephropathy, but the significance of the lesion to renal carcinogenesis is unclear. Elucidating mechanisms of renal cell proliferation are necessary for our understanding of cause and effect relationships. An exciting recent finding is altered expression of transforming growth factor-alpha in hereditary rat renal cell carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmentally regulated transcription of the four liver-specific genes for inter-alpha-inhibitor family in mouse

The inter-alpha-inhibitor family is composed of the plasma-protease inhibitors inter-alpha-inhibitor, pre-alpha-inhibitor and bikunin. Inter-alpha-inhibitor and pre-alpha-inhibitor are distinct assemblies of bikunin with distinct sets from three heavy (H) chains designated H1, H2 and H3. These H chains are encoded by a set of three evolutionarily related H genes, and bikunin by an alpha-1-microglobulin/bikunin precursor gene (AMBP). This precursor is cleaved to yield bikunin, a member of the Kunitz-type protease-inhibitor superfamily, and alpha-1-microglobulin, which belongs to the lipocalin superfamily. Northern-blot experiments with RNAs obtained from various tissues in fetal and in adult mice indicated that the transcription of the four AMBP and H genes is liver-restricted, although there is expression of H3 in brain. An analysis of the H1, H2, H3 and AMBP transcripts, as well as of transcripts for other control genes, in liver during development showed a progressive increase in the amounts of the H1, H2, H3 and AMBP RNAs, which all peak transiently at day 5 after birth. This was shown by a nuclear run-on experiment to originate from a change in transcription rate. The transient and postnatal increase in transcription could be explained neither by the liver-restricted expression nor by a common origin of these four genes, nor by a perinatal requirement for many lipocalins or protease inhibitors. This suggests that all four genes are perinatally triggered at the level of similar elements in their transcriptional regulatory regions, a conclusion strengthened by the weak expression of the four genes that is seen in a mutant mouse strain (albino) that is deficient in some liver-specific transcription factors.

Serum amyloid P (female protein) of the Syrian hamster. Gene structure and expression

The structure and expression of the gene encoding serum amyloid P (SAP) component of the Syrian hamster have been studied by isolation of cosmid clones, nucleotide sequence analyses, and quantitation of nuclear run-on transcripts, nuclear RNA, mRNA, and protein levels. Hamster SAP, originally identified as female protein (FP), is a unique pentraxin because pretranslational expression of this gene is modulated by mediators of inflammation and sex steroids. SAP(FP) levels are high in sera from female hamsters and low in males. The response to inflammation is divergent; SAP(FP) levels decrease in females and increase in males during an acute phase response. The SAP(FP) gene encodes a 211 amino acid residue mature polypeptide as well as a 22-residue signal peptide. The intron/exon organization is similar to that of other pentraxins, but additional transcripts are generated from alternate polyadenylation sites in the 3' region. Circulating levels of SAP(FP) and the corresponding hepatic transcript levels are augmented by estrogen, while testosterone, dexamethasone, and progesterone cause a decrease in these levels. In addition the cytokines interleukin-1, -6, and tumor necrosis factor mediate a decrease in hepatic SAP(FP) transcript levels in female hamsters but did not cause a significant elevation of SAP(FP) mRNA in livers of male hamsters. The differences in expression of the SAP(FP) gene between male and female hamsters and between unstimulated male hamsters and male hamsters stimulated with an injection of lipopolysaccharide are due, at least in part, to alterations in transcription.

Differences in alpha 2u-globulins increased in male rat kidneys following treatment with several alpha 2u-globulin accumulating agents: cystein protease(s) play(s) an important role in production of kidney-type-alpha 2u-globulin

Effects of alpha 2u-globulin accumulating agents on alpha 2u-globulins in rat kidneys were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analysis. Treatment of male animals with decalin (150 mg/kg), 2,2,4-trimethylpentane (50 mg/kg), isophorone (150 mg/kg), d-limonene (150 mg/kg) or 1,4-dichlorobenzene (150 mg/kg) by gavage for 14 consecutive days in each case resulted in a marked intensification of a protein band corresponding to kidney-type-alpha 2u-globulin, with a molecular mass calculated to be approximately 16 kDa. However, intraperitoneal treatment with leupeptin and E-64 (two times 0.07 mmol/kg, for each), well known cystein protease inhibitors, while only slightly increasing this kidney-type-alpha 2u-globulin band, caused the intensification of a approximately 19-kDa molecular mass protein band which was revealed to be a native-type-alpha 2u-globulin by SDS-PAGE and immunoblotting. These results indicated that at least two types of alpha 2u-globulin can be increased in male rat kidney by chemical treatment. Moreover, cystein protease(s) appear(s) to play an important role in the degradation of alpha 2u-globulin and particularly in the conversion of native-type-alpha 2u-globulin to kidney-type-alpha 2u-globulin in rat kidneys.

Spatio-temporal expression of estrogen sulfotransferase within the hepatic lobule of male rats: implication of in situ estrogen inactivation in androgen action

Estrogen sulfotransferase (EST) catalyzes transfer of the sulfate group from phosphoadenosine phosphosulfate to estrogenic steroids. Since estrogen sulfates do not bind to the estrogen receptor with high affinity, EST can control the intracellular level of the receptor-active estrogens. Androgen action in the rat liver, as indicated by the androgenic induction of alpha 2u-globulin, is inhibited by low levels of estrogens. Thus, in situ estrogen inactivation by EST is expected to increase hepatic androgen sensitivity. During the lifespan of the animal, rat liver undergoes three distinct phases of androgen sensitivity, i.e. prepubertal androgen insensitivity, androgen sensitivity after approximately 40 days of age, and androgen insensitivity during senescence (greater than 750 days). EST in the liver is expressed only after puberty, when the liver becomes androgen sensitive. Furthermore, localization of EST and its corresponding mRNA within the lobular unit of the liver demonstrates that only androgen-responsive hepatocytes located around the central vein contain immunoreactive EST and its corresponding mRNA. These temporal and spatial correlations of EST expression and hepatic androgen sensitivity support the concept that steroid-inactivating enzymes play important roles in sex hormone action.

Synthesis of alpha 1-microglobulin in cultured rat hepatocytes is stimulated by interleukin-6, leukemia inhibitory factor, dexamethasone and retinoic acid

The secretion of alpha 1-microglobulin by primary cultures of rat hepatocytes was found to increase upon the addition of interleukin-6 or leukemia inhibitory factor, two mediators of acute phase response. This stimulatory effect was further enhanced by dexamethasone. alpha 1-Microglobulin is synthesized as a precursor also containing bikunin, and the precursor protein is cleaved shortly before secretion. Our results therefore suggest that both alpha 1-microglobulin and bikunin are acute phase reactants in rat hepatocytes. Furthermore, we found that retinoic acid, previously shown to be involved in the regulation of cell differentiation and development, also stimulated alpha 1-microglobulin synthesis. Only free, uncomplexed alpha 1-microglobulin (28,000 Da) was detected in the hepatocyte media, suggesting that the complex between alpha 1-microglobulin and alpha 1-inhibitor 3, found in rat serum, is formed outside the hepatocyte.

Application of molecular encapsulation for toxicology studies: comparative toxicity of p-Chloro-alpha, alpha, alpha-trifluorotoluene in alpha-cyclodextrin vehicle versus corn oil vehicle in male and female Fischer 344 rats and B6C3F1 mice

The application of alpha-cyclodextrin (alpha-CD) as an alternative vehicle for water insoluble and volatile chemicals was investigated in toxicity studies of p-chloro-alpha, alpha, alpha-trifluorotoluene (CTFT). Groups of F344 rats and B6C3F1 mice of each sex were administered CTFT (97% pure) by gavage in either corn oil or alpha-CD aqueous formulations daily for 14 consecutive days. The dose levels used were 10 (mice only), 50, 400, and 1000 mg/kg for corn oil vehicle and 10, 50, and 400 mg/kg (maximum achievable dose at gavage volume of 5 ml/kg) for alpha-CD vehicle. With both vehicles CTFT and alpha 2u-globulin were found to accumulate in the male rat kidney after 14 days of exposure and a dose-related toxic nephropathy was observed at dose of 50 mg/kg or higher. The hepatocellular hypertrophy and cytoplasmic vacuolation of the adrenal cortex which appeared in dosed male and female rats were also found to be independent of vehicle. Clinical pathology findings suggested a mild anemia and cholestasis in rats. With both vehicles no tissue bioaccumulation of CTFT was found in male or female mice. Vehicle-independent hepatocellular hypertrophy and cholestasis were also observed in mice at doses of 400 and 1000 mg/kg. In conclusion, the alpha-CD vehicle does not affect the toxic responses of CTFT in both sexes of both species. The results of the studies suggest that alpha-CD may be an appropriate alternative vehicle for toxicity studies.

Sexual dimorphism and growth hormone regulation of a hybrid gene in transgenic mice

The sexually dimorphic expression of the urinary protein genes of mice (Mup genes) in the liver is mediated by the different male and female temporal patterns of circulating GH. Normal females were induced to male levels when GH was administered by injection to mimic the male GH pattern, showing that expression at the male level does not require a male sex steroid status in addition to intermittent GH. Two Mup-alpha 2u-globulin hybrid transgenes with different Mup gene promoters showed sexually dimorphic expression, and their expression in females increased to male levels upon testosterone treatment. GH-deficient (lit/lit) mice did not express these transgenes, and GH-deficient females did not respond to testosterone treatment, showing that GH was required for induction. Both normal and GH-deficient females were induced to male levels when GH was administered by injection. This is the first report of a transgene responsive to GH. A transgene consisting of a Mup promoter fused to a Herpes simplex virus thymidine kinase reporter sequence also showed sexual dimorphism, although to a lesser degree. It was expressed at the same level in normal females and GH-deficient mice of both sexes and was induced when GH-deficient mice were treated with GH. We propose that this transgene has a basal constitutive expression, possibly due to the absence of any rodent DNA downstream of the promoter. Since expression of the transgene was significantly induced by GH, the GH response is due at least in part to sequences in the promoter region.

Biosynthesis of inter-α-trypsin inhibitor and α1-microglobulin in a human hepatoma cell line

1. Biosynthesis of alpha 1-microglobulin and inter-alpha-trypsin inhibitor was investigated in a human hepatoma cell line HepG-2. 2. alpha 1-Microglobulin was translated as a precursor common with the light chain of inter-alpha-trypsin inhibitor. 3. alpha 1-Microglobulin was synthesized and secreted into the growth medium within 30 min. 4. Processing of inter-alpha-trypsin-inhibitor-related proteins appeared slow and incomplete. The light chain was connected via a chondroitinsulphate to a heavy chain to form a 125,000-Mr protein and secreted within 1-4 hr.

NCI-Black-Reiter (NBR) male rats fail to develop renal disease following exposure to agents that induce alpha-2u-globulin (alpha 2u) nephropathy

The NCI-Black-Reiter (NBR) rat is the only strain of male rat known not to synthesize the hepatic form of the low molecular weight protein, alpha 2u-globulin. In previous studies, NBR rats were shown not to develop renal disease when exposed to decalin, a compound known to induce alpha 2u-globulin nephropathy in other rat strains. The objective of this study was to show that the presence of alpha 2u-globulin (alpha 2u) is essential for the development of this syndrome in rats exposed to 2,2,4-trimethylpentane (TMP), 1,4-dichlorobenzene (DCB), isophorone (IP), PS-6 unleaded gasoline (UG), and d-limonene (d-L). The induction of alpha 2u-nephropathy in F344 male rats with lindane was used as a positive control and this response was contrasted to male NBR and female F344 rats treated with lindane. Five to seven 11-week-old male NBR rats were exposed to TMP (500 mg/kg/day), DCB (500 mg/kg/day), IP (1000 mg/kg/day), UG (500 mg/kg/day), d-L (1650 mg/kg/day), or lindane (10 mg/kg/day) and five 11-week-old male and female F344 rats were exposed to lindane (10 mg/kg/day) by oral gavage on 4 consecutive days. NBR male and F344 male and female rats gavaged with corn oil were incorporated in the study as vehicle controls. The presence of hyaline droplets was assessed in perfusion-fixed kidneys by staining paraffin sections with Mallory-Heidenhein stain and in GMA sections with Lee's methylene basic blue fuchsin stain. Paraffin sections were also analyzed immunohistochemically for the presence of alpha 2u. Under exposure conditions that clearly induce alpha 2u-nephropathy in male F344 rats, no lesions, hyaline droplets, or alpha 2u were detectable in treated or control male NBR and female F344 rats. It is thus concluded that the presence of alpha 2u is causal to the development of renal disease in rats exposed to TMP, DCB, IP, UG, d-L, and lindane.

Plasma protein synthesis and secretion in the visceral yolk sac of the fetal rat: gene expression, protein synthesis and secretion

This report compares the relative levels of messenger RNA species coding for plasma proteins in rat visceral yolk sac and fetal liver from 12.5 days to 21.5 days gestation. Transthyretin, retinol-binding protein, transferrin and alpha 1-fetoprotein mRNAs were detected in both tissues, although relative levels were much higher in the yolk sac compared to fetal liver, in early gestation. Messenger RNA coding for the positive acute phase proteins thiostatin, fibrinogen, alpha 2-macroglobulin and alpha 1-antitrypsin were detected at a low but significant level in yolk sac, while the levels in fetal liver steadily increased from 16.5 days gestation and, with the exception of alpha 1-antitrypsin, reached levels higher than those found in adult liver just prior to birth. Albumin, inter-alpha 1-trypsin inhibitor, alpha 1-acid glycoprotein, haptoglobin, vitamin D-binding protein and ceruloplasmin messenger RNA levels were either very low or undetectable in yolk sac and fetal liver. Secretion of proteins by yolk sac endoderm occurred largely across the basolateral surface, i.e. towards the fetal compartment. These data support the hypothesis that one function of the yolk sac in the rat is the synthesis and secretion of a select group of plasma proteins to maintain homeostasis in the fetal compartment in the period before the fetal liver has matured sufficiently to carry out this function.

Effect of dihydrotestosterone on serum concentrations of alpha 2u-globulin and on spermatogenesis in melatonin-treated rats

Adult male rats were given s.c. injections of melatonin (400 micrograms/100 g body weight per day) for 14 days. On day 15, the weights of the testis and accessory sex organs were less, testicular 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activity was inhibited, spermatogenesis was suppressed and serum levels of gonadotrophins, testosterone and alpha 2u-globulin were decreased compared with control animals injected with vehicle. In a third group of rats given the same dose of melatonin for 14 days, administration of dihydrotestosterone (DHT) at a dose of 25 micrograms/100 g body weight per day on days 8-14 resulted in serum levels of alpha 2u-globulin, FSH, LH and testosterone and testicular 17 beta-HSD activity similar to those seen in vehicle-injected control animals. Weights of the testes and accessory sex organs and spermatogenesis were normal after administration of DHT in melatonin-treated rats. In another group of rats, the depressive effects of melatonin treatment on plasma gonadotrophins were reversed by the administration of alpha 2u-globulin on days 8-14. It was concluded that treatment with DHT prevents the depressive action of melatonin on testicular function by inducing the synthesis of alpha 2u-globulin.

Armenian hamster female protein: a pentraxin under complex regulation

The serum of Armenian hamster (Cricetulus migratorius) contains a protein homologous to female protein (FP) that has been characterized in the Syrian (golden) hamster. Of unknown function, FP belongs to a family of proteins (called pentraxins) that have a common ancestral gene and are widely expressed in nature. Whereas serum concentration of FP in Syrian hamsters (SFP) is many fold greater (200- to 300-fold) in females vs. males, Armenian hamster FP (AFP) is only moderately elevated (approximately 3-fold) in female vs. males and only for the fall-winter months of the year. In the Armenian hamster testosterone administration to females or castration of males has no effect on AFP serum levels, whereas in Syrian hamster these treatments change SFP serum concentration to that characteristic of the opposite sex. Some sex steroid control of hepatic AFP synthesis is evident, however, as serum levels decrease after exogenous estrogen treatment. In contrast to Syrian hamster FP, normal levels of AFP are dependent on an intact hypophysial-pituitary axis and also are influenced by the season of the year. As an acute-phase protein, AFP responds in a typical fashion, with increasing serum levels detected in both sexes in contrast to the divergent sex-limited response in Syrian hamsters. Although AFP and SFP are similar structurally, morphologically, and antigenetically and share common binding specificities, the regulation of FP synthesis in Armenian hamster is very different from that previously found in Syrian hamster.

Differential in vitro transcription from the promoter of a rat alpha 2u globulin gene in liver and spleen nuclear extracts

When used in an in vitro transcription assay, the promoter of a cloned alpha 2u globulin gene is much more active in liver than in spleen nuclear extracts. Promoter deletion experiments suggest that both positive and negative regulatory mechanisms may be involved in the differential in vitro transcription from the alpha 2u globulin promoter in these two nuclear extracts. Interestingly, removal of promoter elements upstream from position -74 results in a significant increase of in vitro transcription in spleen but not in liver nuclear extracts, and thus reduces the difference in transcription observed with longer alpha 2u promoters in these two extracts. Deletion of additional nucleotides to position -43 strongly reduces the in vitro transcription efficiency of the promoter in extracts from both tissues. None of the examined promoters containing between 3000 and 22 nucleotides of 5' flanking regions are differentially transcribed in liver nuclear extracts from either male or female rats. Thus, in contrast to cell-type specificity, sex-specificity could not be observed in our in vitro transcription experiments. DNase I protection experiments with crude nuclear extracts and partially or highly purified nuclear proteins suggests the presence of six recognition sites for DNA-binding factors between the TATA element and position -210. Some of these factors could be identified as proteins that also bind to elements within the albumin gene promoter.

Human inter-alpha-trypsin inhibitor. Synthesis and maturation in hepatoma HepG2 cells

In hepatoma HepG2 cells, human inter-alpha-trypsin inhibitor (ITI) was synthesized as three heavy chains, H-1 (100 kDa), H-2 (110 kDa) and H-3 (113 kDa), and light hybrid chain (49.5 kDa) composed of alpha 1-microglobulin and HI-30 (ITI derivative, human inhibitor of 30 kDa). The association of at least two heavy chains, H-1 and H-3, with the HI-30 part of the light chain gave rise to a molecule similar to serum ITI. A composite protein (approximately 250 kDa) including heavy and light chains was also secreted, while alpha 1-microglobulin and ITI H-2 protein were released as separate entities. Light chain synthesis could be the limiting factor for ITI maturation.

Rapid postexposure decay of alpha 2u-globulin and hyaline droplets in the kidneys of gasoline-treated male rats

Unleaded gasoline induces nephropathy, characterized by rapid accumulation of hyaline (protein resorption) droplets in epithelial cells of the renal proximal convoluted tubules, only in male rats. The hepatic synthesis of the male rat-specific protein alpha 2u-globulin, a constituent of renal hyaline droplets, is unaltered by gasoline treatment (Olson et al., 1987). Renal alpha 2u-globulin content increased to 210% of control within 18 h of a single oral dose of gasoline (2.0 ml/kg); maximal levels (320% of control) were attained following gasoline administration for 3 d. Increases in renal alpha 2u-globulin caused by gasoline were accompanied by concurrent proliferation of hyaline droplets. However, within 3 d of terminating gasoline administration renal alpha 2u-globulin content decreased to the same level as that in unexposed rats, although renal hyaline droplet number returned to pretreatment levels somewhat more slowly. The conjoint effect of postexposure recovery and estradiol (an inhibitor of hepatic alpha 2u-globulin synthesis) administration was also determined in male rats. On postexposure d 3, 6, and 9, estradiol treatment (1 mg/kg, sc, 4 d, starting on d 9 of gasoline treatment) decreased renal alpha 2u-globulin content to 75%, 59%, and 48%, respectively, of that in rats allowed to recover from gasoline with no hormone treatment. Hepatic alpha 2u-globulin content in estradiol-treated rats was decreased by 74%, 97%, and 96% at the same intervals. Estradiol treatment during recovery from gasoline also appeared to increase the removal of accumulated hyaline droplets from the renal cortex. Thus, accumulation of alpha 2u-globulin-containing hyaline droplets after subacute exposure of male rats to gasoline is rapidly reversible, dependent on continuous exposure to gasoline and maintenance of the normal rate of hepatic alpha 2u-globulin synthesis. These results emphasize the dynamic state of renal cortical hyaline droplets and suggest strongly that gasoline hydrocarbons cause hyaline droplet accumulation by prolonging the half-time of degradation of alpha 2u-globulin.

Changes in transcriptional activity and matrix association of alpha 2u-globulin gene family in the rat liver during maturation and aging

Hepatic synthesis of alpha 2u-globulin in the male rat begins at puberty (about 40 days), reaches a peak level at about 80 days, and ceases at about 750-800 days of age. The age-dependent changes in alpha 2u-globulin synthesis are correlated with both the steady-state level of the hepatic mRNA for this protein and the rate of transcription of the alpha 2u-globulin gene family. Transcriptional activation of the alpha 2u-globulin gene family at puberty and cessation of transcription at senescence correlate with the association and dissociation of this gene domain with the nuclear matrix. Unlike the alpha 2u-globulin gene, the albumin gene in the liver shows preferential association with the nuclear matrix throughout the life. From these results we conclude that the age-dependent changes in alpha 2u-globulin synthesis are due to the alteration in the rate of transcription of the alpha 2u-globulin gene, and that the association of this gene domain to the nuclear matrix is a prerequisite to its transcriptional activation.

Rapid androgenic stimulation of alpha 2u-globulin synthesis in the perfused rat liver

Hepatic synthesis of alpha 2u-globulin and its mRNA in the male rat is dependent on androgen, glucocorticoid, T4, insulin, and GH. Some of these hormones may act directly on the liver, while others may influence alpha 2u-globulin synthesis through indirect physiological changes. In the present study the specific role of androgen in the synthesis of alpha 2u-globulin was examined in an in vitro liver perfusion system. The addition of 5 alpha-dihydrotestosterone to the medium perfused through livers from castrated rats resulted in a rapid increase (approximately 10-fold over the vehicle control within 120 min) in the circulating level of alpha 2u globulin. Labeling with [35S]-methionine showed that the androgen-mediated increase in the circulating level of alpha 2u-globulin is due to release of the newly synthesized protein. Quantification of alpha 2u-globulin mRNA in the perfused livers with and without androgen supplementation indicated that the increased mRNA level can only partially account for the elevation of the circulating level of this protein. From these results it is concluded that androgen can act directly on the liver to stimulate alpha 2u-globulin synthesis, and the hormone may influence more than one regulatory step.

Independent regulatory influence of growth hormone on the hepatic synthesis of alpha 2u-globulin

Administration of GH through sc injections to hypophysectomized male rats induces the hepatic mRNA for alpha 2u-globulin (a male-specific urinary protein) from an undetectable level to 43.4% of the normal male level. The same treatment administered to hypophysectomized-gonadectomized rats and androgen-insensitive Tfm rats induces alpha 2u-globulin mRNA to a level of only 5-10% of that in the normal male. However, none of these types of animals shows an appreciable response when GH is administered continuously through osmotic minipumps. Perfusion of the livers derived from hypophysectomized male rats with the blood from hypothyroid rabbits (also deficient in GH) was used to examine in vitro effects of GH on alpha 2u-globulin synthesis. Supplementation of the perfusion medium with GH and T4 failed to induce alpha 2u-globulin within the perfusion period of 120 min. These results show that GH can influence alpha 2u-globulin synthesis independent of the androgen and that the mode of administration of GH plays an important role in its biological response.

Effect of age and dietary restriction on the expression of alpha 2u-globulin

The effect of aging on the expression of alpha 2u-globulin was studied in liver tissue from 6-30-month-old male Fischer F344 rats. The synthesis of alpha 2u-globulin by suspensions of isolated hepatocytes decreased 90% between 6 and 22 months of age. The levels of alpha 2u-globulin mRNA and the transcription of alpha 2u-globulin genes by isolated liver nuclei decreased 80-85% between 5 and 24 months of age. Because alpha 2u-globulin has been suggested to be a "senescence marker protein," the expression of alpha 2u-globulin was measured in rats fed a diet restricted in calories. This dietary restriction procedure has been shown to increase significantly the longevity of rodents. The expression of alpha 2u-globulin was compared in liver tissue from 18-month-old rats fed ad libitum and a restricted diet (40% restriction of total calories). The synthesis, mRNA levels, and transcription of alpha 2u-globulin were 1.8-3-fold higher for liver tissue from restricted rats compared to liver tissue from rats fed ad libitum. Therefore, dietary restriction alters the age-related change in the expression of alpha 2u-globulin. Our results demonstrate that the changes in alpha 2u-globulin expression that arise during aging or dietary restriction are regulated at the level of transcription.

Sex-independent synthesis of alpha 2u-globulin and its messenger ribonucleic acid in the rat preputial gland: biochemical and immunocytochemical analyses

alpha 2u-Globulin is the principal urinary protein of the mature male rat. The major urinary source of this protein is the liver where it is synthesized and secreted by hepatocytes under hormonal regulation. High levels of alpha 2u-globulin and its messenger RNA (mRNA) are also present in the preputial gland of both male and female rats, and neither castration nor ovariectomy significantly alters the preputial concentration of this protein and its mRNA. Per unit mass of RNA and protein, the preputial gland as compared to liver contains about 3-fold higher level of alpha 2u-globulin mRNA and about 300-fold higher level of alpha 2u-globulin. Despite a 3-fold (300%) difference in the content of alpha 2u-globulin mRNA, nuclear run-off experiments show only a 30% higher rate of alpha 2u-globulin gene transcription in the preputial gland than in the liver. Immunocytochemical analyses reveal that the liver possesses two alpha 2u-globulin cell populations, one showing higher immunoreactivity than the other. In contrast, the preputial gland contains only one type of alpha 2u-globulin containing acinar cells, and a large amount of alpha 2u-globulin accumulates in the ductal lumen. From these results we conclude that the 300% higher level of alpha 2u-globulin mRNA in the preputial gland is not due to a corresponding difference in the rate of transcription of alpha 2u-globulin gene. Such a difference may represent tissue-specific regulation at a posttranscriptional level of mRNA metabolism. Furthermore, the huge difference in the alpha 2u-globulin content of the preputial gland and the liver is primarily due to the cellular and ductal accumulation of this protein in the preputial gland vs. its rapid secretion by the liver.