Messenger RNA for alpha 2u-globulin of rat liver. Purification, partial characterization of the mRNA, and synthesis of a Hae III restriction fragment as its cDNA probe

The mRNA for the androgen-dependent hepatic protein, alpha 2u-globulin is normally present in the liver of mature male rats to the extent of about 1% of the total mRNA population. alpha 2u mRNA which was found to migrate as a 14 S band was purified about 18-fold through preparative urea-agarose gel electrophoresis. 32P-Labeled cDNA synthesized with this partially purified alpha 2u mRNA was used as substrate for two restriction endonucleases Hha I and Hae III. Digestion of the cDNA with Hha I failed to reduce its electrophoretic heterogeneity. However, Hae III digestion of the cDNA preparation greatly reduced the molecular complexity and produced several distinct cDNA bands. One of these Hae III fragments (Band A) containing 410 nucleotide residues was extracted from polyacrylamide gel and found to be complementary to alpha 2u mRNA. The identity of this cDNA fragment was established by its ability to inhibit selectively the translation of alpha 2u mRNA in the rabbit reticulocyte cell-free system and by its hybridization kinetics with poly(A)+ hepatic RNA from animals with different rates of alpha 2u synthesis. The relative R0t 1/2 values showed a direct correlation between mRNA sequences complementary to the cDNA fragment (A) and to both translatable alpha 2u mRNA and hepatic level of alpha 2u-globulin in adult male, female, and maturing male rats. Thus, the cDNA fragment containing 410 nucleotide residues generated by the restriction cleavage with Hae III can be used as a convenient probe for identification and quantitation of alpha 2u mRNA under different physiological and experimental conditions.

Multiple hormone requirement for the synthesis of alpha 2u-globulin by monolayers of rat hepatocytes in long term primary culture

Primary cultures of adult rat hepatocytes were prepared by releasing liver cells through fractional trypsinization and by a novel nonenzymatic procedure involving the imprinting of liver explants on the surface of the culture flask (explant imprinting). The comparative properties of these two primary cultures and their abilities to synthesize alpha 2u-globulin under multihormonal stimulation were investigated. The hepatocytes isolated from male rats by fractional trypsinization were found to divide rapidly and form a confluent monolayer within 5-7 days of culture. However, these cells failed to synthesize alpha 2u-globulin even after treatment with 5 alpha-dihydrotestosterone, GH, T3, and dexamethasone, hormones with known stimulatory effects on the synthesis of alpha 2u-globulin in vivo. On the contrary, hepatocytes prepared from male rats by the nonenzymatic procedure of explant imprinting were found to synthesize alpha 2u-globulin for more than 2 weeks and responded to GH, T3, and dexamethasone with enhanced production of this protein. Fortification of the culture medium with all of the above three hormones caused an approximately 9-fold enhancement of alpha 2u production within 4 days of culture compared to production in control culture without these hormones. The above results substantiate earlier findings concerning the multiple hormonal requirement for hepatic synthesis of alpha 2u-globulin in vivo and show that isolation and culture of hepatocytes by nonenzymatic explant imprinting may serve as a useful procedure for studying endocrine regulation of gene activity in vitro.

Regulation of gene expression in primary cultures of adult rat hepatocytes on collagen gels

The studies described in this paper demonstrate rather conclusively the efficacy of the study of the regulation of gene expression in primary cultures of adult rat hepatocytes. The utilization of these cells in completely defined medium allows one to determine the exact environmental conditions for the regulation of the expression of specific genes. In the studies described in this work, we have demonstrated that the regulation of glucokinase involved three hormones, insulin, corticosteroids, and T3. In contrast, the regulation of an enzyme involved primarily in fatty acid metabolism, ATP-citrate lyase, required only insulin and T3 for its full expression. Cyclic GMP appeared to be involved in the regulation of glucokinase, but not ATP-citrate lyase, a fact that would be extremely difficult to demonstrate clearly in vivo. The regulation of the gluconeogenic enzyme, ornithine aminotransferase, in vitro involved only a single hormone, glucagon, the inhibition of induction by corticoid steroids demonstrable in vivo being absent in cell culture. However, the repressive effect of glucose on the induction of this enzyme was quite comparable to that seen in vivo and was not mediated through cyclic AMP or insulin, based on findings in cell culture. Thus, the requirements for and the mechanisms involved in enzyme induction and repression by hormones and glucose may be much more easily studied in primary cultures of rat hepatocytes than in vivo, or even in hepatoma cell lines, where relatively few genes are expressed as compared with adult liver. In addition to the regulation of enzyme levels, the characteristics of protein secretion may be investigated in primary cultures of rat hepatocytes and compared with the biochemical and physiological parameters in the whole organism. This was exemplified by the study of the synthesis and secretion of alpha 2u-globulin that was secreted into the culture medium in both glycosylated and nonglycosylated forms but was maintained in the circulation in vivo, principally as the glycosylated form. Furthermore, the function of glycosylation in this particular instance may be deduced from a combination of the in vivo and in vitro approaches. The advantages of the use of primary hepatocyte cultures for the study of the regulation of gene expression in mammalian tissue has only recently been explored. Future investigations of the regulation of a variety of enzymes in these cultures as well as a study of the regulation of the synthesis of their messenger RNA are now possible and should provide an exciting system in which to understand at a molecular level the regulation of the expression of a number of genes.

[Features of the biosynthesis of immunoglobulin G peculiar to the growth process]

It is established that with partial hepatectomy, Shvets leukosis and hepatoma RS-1 the biosynthesis intensity of rat blood serum proteins producing aggregates in the acid medium is considerably higher than that of other serum proteins, the incorporation of the radioactive precursor into immunoglobulin G peculiar to intensive normal and malignant growth being particularly intensive. During liver regeneration as well as in malignant growth specific radioactivity of immunoglobulin G peculiar to the growth processes is three and five times, respectively, as high as this value for blood serum soluble proteins and proteins of alpha-globulin fractions.

A rat serum glycoprotein whose synthesis rate increases greatly during inflammation

Crossed immunoelectrophoresis of rat serum demonstrated considerably increased serum concentrations of at least ten different proteins during turpentine-induced inflammation. One protein, which moved during electrophoresis like an alpha 1 globulin, showed a particularly large increase. This protein was purified to homogeneity by ammonium sulfate fractionation followed by chromatography on DEAE-cellulose. Sephadex G-100, and concanavalin A-Sepharose, and finally disc electrophoresis in polyacrylamide gel. It has a molecular weight of 56,000 determined by equilibrium ultracentrifugation. An apparent molecular weight of 68,000 was estimated for the reduced protein by electrophoresis in polyacrylamide gel plus sodium dodecyl sulfate, suggesting that the native protein is composed of a single polypeptide chain. It has an E2801%, 1 cm of 5.2, an isoelectric pH of 4.7, and contains 19% carbohydrate. The protein does not inhibit bovine trypsin or chymotrypsin. Its physical properties and amino acid composition distinguish this protein from all other rat serum proteins hitherto characterized. During acute inflammation, induced 25 h previously, rats incorporated 20 times more [14C]leucine into this particular protein than did normal rats. However, incorporation into total serum protein during acute inflammation increased only slightly. Regardless of whether inflammation was induced by surgical injury or by a subcutaneous turpentine injection, within 48 h the serum concentration of this major acute-phase protein rose from the normal value of 0.46 g/liter to a maximum value of 7.2 g/liter, which constituted 10% of the total serum protein.

Synthesis and secretion of alpha 1-microglobulin by human lymphocytes

alpha 1-Microglobulin (alpha 1-m) was purified by column chromatography from a supernatant fluid of cultured T and B lymphocytes stimulated with mitogens. This protein had a molecular weight of 33,000 as determined by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis, migrated in the alpha 1-region on immunoelectrophoresis and proved immunologically identical to alpha 1-m which had been purified from the urine of patients with renal tubular disorders. Using indirect immunofluorescence, alpha 1-m was detected on the surface of both T and B lymphocytes, displaying the same intensity on each cell type. These findings indicate that alpha 1-m is actively produced and secreted by T and B lymphocytes.

Cycloheximide inhibition of hormonal induction of alpha 2u-globulin mRNA

The induction of hepatic alpha 2u-globulin synthesis by glucocorticoids in isolated hepatocytes occurs via an increase in the level of its mRNA as measured by cell-free translation and by hydbridization to an alpha 2u-globulin cDNA probe. To explore whether induction of this mRNA is a direct or an indirect consequence of the interaction of the dexamethasone-receptor complex with the alpha 2u-globulin genome, the requirement for ongoing protein synthesis was examined. Concentrations of cycloheximide too low to prevent precursor incorporation into total poly(A)-containing RNA do prevent the hormonal induction of alpha 2u-globulin mRNA. Furthermore, incorporation of 3H-labeled amino acids into total protein was decreased by only 40-50%, and the appearance of the dexamethasone-induced glycosylated forms of alpha 2u-globulin was completely prevented in these cycloheximide-treated hepatocytes. The results suggest that the synthesis of a protein mediator(s) may be required for the induction of alpha 2u-globulin mRNA by glucocorticoids and that the steroid-receptor complex may not interact directly with the alpha 2u-globulin genome.

Superinduction of alpha 2u globulin by actinomycin D: evidence for drug-mediated increase in alpha 2u mRNA

Actinomycin D, an inhibitor of DNA-dependent RNA synthesis, increased the hepatic concentration of alpha 2u globulin, an androgen-inducible protein in the rat. Spayed female rats with a marginally induced state of alpha 2u synthesis showed an approximately 5-fold increase in hepatic alpha 2u globulin within 3-6 hr after treatment with actinomycin D. Initial treatment of these animals with 5 alpha-dihydrotestosterone, followed by actinomycin D, resulted within 2-3 hr in a more than 2-fold increase in hepatic alpha 2u globulin compared to animals treated with the androgen alone. In spite of inhibition of hepatic synthesis of poly(A)-containing RNA to less than 25% of control, superinduction with actinomycin D resulted in a parallel increase in the translatable mRNA for alpha 2u globulin. These results showing increase in both alpha 2u globulin and its translatable mRNA after superinduction with actinomycin D support the concept of post-transcriptional repression of alpha2u synthesis.

Models for mRNA translation: theory versus experiment

Three models for mRNA translation are discussed in the light of available experimental data. It is concluded that the elongation rates vary along a messenger, possibly as a result of a coupling between ribosome movement and mRNA secondary structure. Some promising areas of further experimentation are indicated.

Hormonal induction of alpha2u-globulin synthesis in isolated rat hepatocytes

Hepatocytes freshly prepared with collagenase synthesize alpha 2u-globulin and other hepatic proteins in vitro at approximately the same rate throughout 30 h of incubation. The newly synthesized proteins are efficiently secreted into the medium throughout this period. That the secretion of proteins by hepatocytes is not due to cell leakage is shown by the fact that 30 micrometer colchicine prevents the appearance of labeled alpha2u-globulin and other proteins in the medium. Hepatocytes isolated from animals in different endocrine states synthesize alpha2u-globulin in vitro at rates consistent with the hormonal effects upon its in vivo biosynthesis. In vitro addition of androgens to hepatocytes isolated from castrated male rats evokes an elevation of general protein synthesis in these hepatocytes. Glucocorticoids, added in vitro, specifically induce and elevated rate of alpha2u-globulin synthesis.

Hepatic synthesis and urinary excretion of alpha2u-globulin by male rats: diurnal rhythm and response to fasting and refeeding

The urine of sexually mature male rats contains a protein of hepatic origin, alpha2u-globulin, not found in the urine of immature or female rats; output of this protein is greatly reduced by fasting. We have examined the effects of feeding and of fasting for various lengths of time on urinary output and hepatic synthesis of alpha2u-globulin. Rats eating ad libitum showed diurnal rhythms of urinary alpha2u-globulin excretion reaching maxima between 2000 and 0800 hours, thus coinciding with the daily feeding period of the rat. Fasting for 12 hours extinguished this diurnal rhythm. When fasting was prolonged up to 36 hours, urinary excretion of alpha2u-globulin was reduced to very low levels. Hepatic synthesis of alpha2u-globulin under these nutritional conditions was investigated by incubating liver polyribosomes with [3H]leucine and a preparation of soluble enzymes for protein synthesis and separating the labeled alpha2u-globulin peptides by immunoprecipitation followed by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. By this technique, it was shown that only membrane-bound ribosomes in the livers of mature male rats make this protein. Semi-quantitative measurement suggested that the proportion of liver polyribosomes synthesizing alpha2u-globulin was unchanged after 12 hours of fasting, but was reduced after 24 and 36 hours of fasting. It is proposed that the diurnal rhythm in alpha2u-globulin output in the urine represents translational control of its synthesis in the liver, whereas the more extensive reduction with prolonged fasting is partly due to a selective reduction in transcription of the messenger RNA for this protein.

Sexual difference in the effect of cyproterone acetate and glucocorticoids on alpha2u-globulin in gonadectomized rats

Laboratorium voor Experiméntele Geneeskunde, Katholieke Universiteit Leuven, Rega Instituut, Minderbroedersstraat 10, B-3000 Leuven, Belgium

(Received 28 March 1978)

The synthesis of α2u-globulin, the major protein found in the urine of adult male rats (Roy & Neuhaus, 1966; Roy, Neuhaus & Harmison, 1966), is controlled by several hormones. Androgens, growth hormone, thyroxine and glucocorticoids promote the synthesis of this protein, whereas oestrogens and a factor secreted by ectopically transplanted pituitary glands suppress it (Roy & Neuhaus, 1967; Roy, 1973; Kurtz, Sippel & Feigelson, 1976; Vandoren, Van Baelen, Verhoeven & De Moor, 1978). Cyproterone acetate (CA), a potent antiandrogen, inhibits the androgenic induction of α2u-globulin in ovariectomized rats, but does not suppress its synthesis in intact male rats (Roy, 1976). In the present experiments, the influence of CA on the induction of α2u-globulin by testosterone propionate (TP) in the serum of gonadectomized male and female rats was compared. Evidence is presented for

Transcription of the alpha2u-globulin gene in male rat liver nuclei in vitro

Alpha2u-globulin is a male rat liver protein under multihormonal control which represents approximately 1% of hepatic protein synthesis. We have measured the rate of transcription of the alpha2u-globulin gene using a nuclear cell-free transcriptional system with mercurated CTP as substrate for the endogenous RNA polymerases. The newly synthesized, mercurated RNA was purified free of endogenous RNA by chromatography on sulfhydryl agarose and hybridized to 3H-labeled alpha2u-globulin cDNA. It was found that, in male rat liver nuclei, alpha2u-globulin RNA sequences represent 0.005% of the total newly synthesized RNA. Actinomycin D or alpha-amanitin completely blocks the synthesis of alpha2u-globulin RNA in these nuclei. No alpha2u-globulin RNA synthesis was detectable in female rat liver nuclei. Thus, within the limits of our detection the absence of hepatic alpha2u-globulin mRNA in female rats appears to be due to a lack of transcription of the alpha2u-globulin gene in these animals.

[Placental origin of the progesterone binding protein in the pregnant guinea pig; immunohistoligical study]

The origin of the high affinity progesterone binding protein (PBP) occurring during pregnancy in the guinea pig serum has been investigated. An indirect immunofluorescence technique has been developed using a specific antiserum raised in rabbits. An accumulation of PBP-like immunofluorescent material was detected in the trophoblastic syncytium of the placenta tissue, whereas all other examined pregnant guinea pig organs gave negative reactions. It is concluded that this placental accumulation of immunoreactive PBP-like material may express a placental biosynthesis of this glycoprotein.

Synthesis of alpha-fetoprotein and some other serum proteins in testicular tumors

Serum levels of alpha-fetoprotein were determined in 33 patients with testicular germ cell tumors and were normal in 11 patients with seminoma and in one patient with matured teratoma; high levels were observed in 19 of 21 patients with embryonal carcinoma, teratocarcinoma, or a mixed type of these germ cell tumors. Tissues from the testicular germ cell tumors were cultivated with 14C-labeled leucine. After incubation, the culture media were subjected to immunoelectrophoretic and autoradiographic analyses. The results were: (i) Radioactive alpha-fetoprotein, albumin, transferrin, and alpha1-globulin appeared in the culture media of embryonal carcinomas obtained from two infants. (ii) Radioactive albumin and alpha1-globulin appeared in the culture media of a mixed type tumor metastasized from testis to retroperitoneal region. (iii) No such radioactive proteins appeared in the culture media of primary seminomas.

Production of slow alpha2-globulin in the pregnant rat

Slow alpha2-globulin (salpha2G), a high molecular weight glycoprotein, appears as a component of rat serum in a wide variety of both physiologic and pathologic conditions, including pregnancy; it is also present in the neonate. In the present study, the protein was detectable in serum after 6 to 10 days, and was present at moderate levels on day 13, and thereafter through the rest of pregnancy. From immunofluorescent localization and 14C-labelled amino acid incorporation studies, salpha2G was found to be localized in uterine and placental tissues and to be synthesized by these tissues as early as day 6 of gestation. Production continued throughout pregnancy. Synthesis in the liver of the pregnant rat began at day 17 of gestation, which is in contrast with the observation in pathologic conditions that liver synthesis is an initial source of the serum protein; substantial fetal liver synthesis was occurring at day 21 of gestation, and the amount in fetal serum was four times greater than that in maternal serum at that time. It is likely that the fetal liver produces salpha2G as soon as it begins to function.