Net glucuronidation in different rat strains: importance of microsomal beta-glucuronidase

The net glucuronidation of bilirubin (BR) has been determined in inbred and outbred rat strains and their subpopulations with similar glucuronosyltransferase (EC 2.4.1.17) activity but with different levels of beta-glucuronidase (beta G) (EC 3.2.1.31), or in which the level of beta G activity was reduced with D-glucaro-1,4-lactone. These studies demonstrated that outbred rat strains consist of two subpopulations that differ approximately 1.5- to two-fold in serum and liver beta G activity. Evidence is presented indicating that owing to its compartmentalization the lysosomal beta G, unlike the corresponding microsomal enzyme, is neither inhibited by glucarolactone nor accessible for hydrolysis of newly synthesized glucuronides. The ratio of glucuronidated to unconjugated BR 15 min after injection of albumin-bound BR into the tail vein appears to correlate negatively with the liver microsomal beta G activity. The results may be relevant to the relative risk to toxins, including carcinogens, and to their reduction by dietary intervention.

Active transport of messenger ribonucleoprotein particles in a reconstituted cell-free system

The ability of a reconstituted cell-free system to transport mRNA as a ribonucleoprotein particle has been examined. Poly(A) messenger ribonucleoproteins (mRNPs), UV cross-linked after release from isolated liver nuclei in a cell-free system, exhibited a buoyant density of 1.33 g/cm3 in cesium sulfate and 1.47 g/cm3 in cesium chloride, values identical to those of poly(A) mRNP isolated directly from liver polysomes. Furthermore, the in vivo and in vitro transported mRNP showed a similar degree of resistance to RNase digestion and had sedimentation coefficients approximately 2.5 times that of the isolated mRNA. Release of both total mRNA and alpha 2 mu-globulin mRNA was proportional to the concentration of a specific cytoplasmic protein. Removal of the transport proteins from the cytosol with streptomycin sulfate provided a basal system incapable of supporting the active transport of alpha 2 mu-globulin mRNA. Hybridization of released RNA with a recombinant probe specific for intron 6 of alpha 2 mu-globulin showed that intron sequences were retained within the nucleus under optimal alpha 2 mu-globulin mRNA transport conditions and that the transported alpha 2 mu-globulin mRNA was of mature size.

Dietary glucarate-mediated reduction of sensitivity of murine strains to chemical carcinogenesis

Serum beta-glucuronidase activity is shown to differ quantitatively in the following strains of mice, listed in order of increasing activity: C3H, C57BL/6 less than BALB/c, DBA/2, ICR less than SENCAR, A/He. The level of the enzyme in the murine strains is shown to correlate with the urinary excretion of 17-ketosteroids, which in turn reflects the endogenous level of androgens. Dietary calcium D-glucarate, an in vivo beta-glucuronidase inhibitor, reduced the steady state level of both beta-glucuronidase and 17-ketosteroid excretion in the highly susceptible A/He and SENCAR strains to that of strains known to be resistant to chemical carcinogenesis. Sensitivity of the A/He strain is significantly reduced by dietary calcium glucarate, which is shown to inhibit DNA binding and the induction of pulmonary adenomas by benzo[a]pyrene.

beta-Glucuronidase levels in patients with fibrocystic breast disease

Certain enzymes in tissues and body fluids may, through reversal of the detoxification process, influence the composition and availability of steroid hormones, toxins, and carcinogens. The ubiquitous enzyme beta-glucuronidase, which hydrolyzes glucuronide conjugates, thereby reversing one of the main detoxification and excretion pathways, was found to vary in concentration in different cysts over a 300-fold range. The distribution was a continuum, devoid of discrete sub-populations. Evidence obtained on selected cyst fluids of high and low beta-glucuronidase activities indicated that the level of the enzyme significantly influenced the ratio of unconjugated: glucuronidated estradiol. The patients with fibrocystic breast disease fell into 2 distinct subpopulations on the basis of their serum beta-glucuronidase activity. In one group the activity was near normal, while in the second group the average serum beta-glucuronidase activity was 3-fold higher than in the women who did not have benign breast disease.

Dietary glucarate as anti-promoter of 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis

Using as a criterion the inhibition of serum beta-glucuronidase activity, dietary calcium D-glucarate is shown to serve as an efficient slow-release source in vivo of D-glucaro-1,4-lactone, the potent endogenous inhibitor of this enzyme. Using the 7,12-dimethylbenz[a]anthracene model of mammary tumor induction in rats it is shown for the first time that feeding the rats calcium D-glucarate-supplemented diet after treatment with the carcinogen, inhibits tumor development by over 70%. Supportive evidence is presented for the theory that calcium D-glucarate inhibits or delays the promotion phase of mammary carcinogenesis by lowering endogenous levels of estradiol and precursors of 17-ketosteroids. Therefore, dietary glucarate can be used to lower blood and tissue levels of beta-glucuronidase, and in turn of those carcinogens and promoting agents which are excreted, at least in part, as glucuronide conjugates.

Chemical carcinogens as specific inducers of a 60-kilodalton oncofetal protein in rats

A 60-kd oncofetal protein which is released to circulation in vivo from tumor cells, or from normal tissues following carcinogen-treatment, has been evaluated against single dose regimens of 18 known chemical carcinogens and 13 known chemical non-carcinogens. The carcinogens included genotoxic and presumed non-genotoxic compounds and the blood plasma 21 days post-treatment of rats with the chemicals was measured. All carcinogens tested transiently induced the 60-kd factor, while none of the non-carcinogens, which included non-carcinogenic analogs or toxins, induced the factor. The results suggest that the early induction of this oncofetal protein may be an indicator of carcinogenicity. The induction of reversible phenotypic changes in normal cells by tumor promoters did not induce the 60-kd factor. Following the carcinogen-mediated transient induction, persistent production of the 60-kd factor occurred at later times if a tumor developed.

Analysis of nuclear RNA processing and transport by temperature perturbation of a cell-free system from mammalian cells

The similarity of the Arrhenius plots relating temperature to messenger RNA (mRNA) transport from intact and membrane-denuded rat liver nuclei demonstrates that the ATP and cytosol-dependent transport is independent of the lipid phase of the nuclear membrane. This temperature dependence of RNA release was confirmed for alpha 2u-globulin mRNA by use of a recombinant DNA probe. Ribosomal RNA (rRNA) release showed a similar temperature dependence, suggesting that both mRNA and rRNA share a common temperature-sensitive step. The kinetics of RNA release at different temperatures suggest that RNA transport from mammalian cell nuclei is a rate-controlled rather than a graded unlocking phenomenon. The processing of mRNA precursors also exhibits a temperature dependence as shown by the linear increase in the ratio of total alpha 2u-globulin RNA to alpha 2u-globulin precursor as a function of time at 30 degrees C but not at 14 degrees C in spite of residual transport at the lower temperature. This temperature dependence of mRNA processing was confirmed by Northern blot analysis of the nuclear RNA following a 45 min incubation. Thus, both the processing and transport of RNA show temperature-sensitive steps when analyzed in cell-free systems derived from mammalian cells.

Immunological identity of a 60 kd oncofetal protein induced in rats by chemical carcinogens and released by transformed cells

A 60,000 dalton (60 kd) oncofetal protein was previously shown to be produced by tumors in tumor-bearing rats and by target tissues within 3 weeks of carcinogen treatment. The factor is released to and accumulates in the blood in vivo and in the conditioned medium of cultured transformed cells in vitro. A polyclonal antibody produced against the 60 kd factor purified from the plasma of a rat carrying the N-2-fluorenylphthalamic acid-induced transplantable Hepatoma 7777, was tested against the 60 kd factor from various sources. Based on the results of immunoprecipitation of biochemical activity associated with the 60 kd factor, it was determined that these anti-60 kd antibodies cross-reacted with the factor released by a dimethylbenzanthracene-induced rat mammary carcinoma, with the factor in rat tumor cytosol and with rat spontaneous lymphoma cells, but not with a 60 kd factor isolated from pooled cancer patient plasma. Furthermore, these antibodies cross-reacted with the 60 kd factor induced within 21 days of treatment of the rats with a range of carcinogens from 8 chemical structural groups. The anti-60 kd factor antibodies did not cross-react with a 35 kd factor having similar biochemical activity found in normal adult cells.

Endogenous and exogenous factors affecting ribosomal RNA release from rat liver nuclei in a cell-free system

rRNA release from isolated liver nuclei has been analyzed in a reconstituted cell-free system using density-gradient analysis and hybridization to a specific recombinant DNA probe to monitor the process. The cell-free system was shown previously to be energy- and cytosol-dependent and to support the formation and release of functional ribosomal subunits. The release of rRNA is now shown to have an absolute dependence on a 70000 dalton cytosol protein. Although in vivo studies suggest that chronic administration of thioacetamide may block formation of a protein involved in the nucleocytoplasmic transfer of ribosomes, the 70000 dalton transport factor is not affected by the treatment. Rather the defect appears to be localized to the nucleus, since it cannot be reversed with normal cytosol from a homologous source. Early stages of nRNA processing appear to be affected by thioacetamide, although additional effects on transport are not ruled out.

Inhibition of 7,12-dimethylbenzanthracene-induced rat mammary tumorigenesis by 2,5-di-O-acetyl-D-glucaro-1,4:6,3-dilactone, an in vivo beta-glucuronidase inhibitor

2,5-Di-O-acetyl-D-glucaro-1,4:6,3-dilactone ( DAGDL ) is a slow release form of D-glucaro-1,4-lactone (GL), a non-toxic natural inhibitor of beta-glucuronidase. When administered orally to female rats in conjunction with a carcinogenic dose of 7,12-dimethylbenzanthracene (DMBA), this compound caused a 70% reduction in the number of rats with mammary tumors and 72% reduction in the number of mammary tumors per rat. Co-administration also reduces the induction by DMBA of a 60 kd oncofetal protein, previously shown to be associated with carcinogenesis and tumorigenesis. DAGDL administration depressed beta-glucuronidase activity both in the absence and presence of concurrent treatment with DMBA and also markedly reduced binding of DMBA to organ DNA. The anti-carcinogenic effect of DAGDL appears to be independent of route of administration of DMBA. It is proposed that inhibition of beta-glucuronidase increases the proportion of DMBA which is sequestered and excreted as the glucuronide and therefore unavailable for activation to the proximal carcinogen.

Nucleocytoplasmic release of repetitive DNA transcripts in carcinogenesis correlates with a 60 kilodalton cytoplasmic protein

Treatment of rats with the hepatocarcinogen 3'-methyl-4-dimethylamino-azobenzene (3'-MeDAB) causes the appearance in the liver cytosol of a 60 kilodalton oncofetal protein. The appearance of this factor occurs within 40 h of treatment and coincides with the increase in the amount of rapidly labeled RNA released from nuclei in a reconstituted cell-free system. Cross-over experiments show that this increase is due to an enhanced transport capacity of the cytosol. The 60 kilodalton RNA transport factor is also present in the cytosol of tumor cells. Addition of the 60 kilodalton factor to normal liver cytosol causes the transport of repetitive RNA sequences similar to those transported from liver nuclei to tumor cell cytosol and those transported to the tumor cell cytoplasm in vivo. This factor modifies nuclear RNA restriction, at least in part, by eliciting the transport of repetitive RNA normally retained within the nucleus of the normal cell.

Absence of the cancer-associated factor with a molecular weight of 60,000 from the plasma of patients with a spectrum of nonneoplastic conditions

We demonstrated previously (Cancer Res., 42: 4964-4969, 1982) that a tumor-associated factor was consistently present in the plasma of over 100 human cancer patients with tumors at 31 different sites. The plasma of healthy controls had very low activity in the biochemical assay. In the present study, we show by a combination of molecular sieving and assay of nuclear RNA transport that the tumor-associated factor, which has a molecular weight of 60,000, is undetectable in the plasma of healthy adults. The low activity reported earlier is due to three normal cell factors of markedly different molecular weight. Furthermore, the tumor factor is shown to be absent from the plasma of male and female patients hospitalized for a variety of nonmalignant surgical conditions. Only the plasma from patients who were pregnant, suffered from chronic renal failure, or had recent myocardial infarction gave false positives in the biochemical assay. However, in these cases, the activity was due to an increase in the normal tissue-associated factors and not to the appearance of the Mr 60,000 tumor-associated factor. The factor is present in amniotic fluid, confirming that it is a fetal factor which does not cross the placental barrier. Thus, it may be classified as an oncofetal factor. All four factors found in the plasma were identified in the cytosol from a human tumor. In summary, the tumor-associated factor appears to be tumor specific and can be unambiguously identified by bioassay of the plasma factors eluting from Sepharose CL-6 B columns in the Mr 60,000 region. It can also be identified by examination of sodium dodecyl sulfate:polyacrylamide gel electrophoretograms of the appropriate Sepharose CL-6 B fractions after removal of albumin.

Characterization of a 60,000-dalton oncofetal protein from the plasma of tumor-bearing rats

A tumor cell-associated protein, previously shown to be present in the circulation of carcinogen-treated and tumor-bearing animals and cancer patients, has now been identified in the cytosol of embryonic tissue. This oncofetal protein, which is absent from the plasma of normal animals, has been purified from the plasma of tumor-bearing rats by a series of steps including ammonium sulfate fractionation and chromatography on Sepharose CL-6B and on CM Affi-Gel Blue. The tumor and fetal-associated 60-kd rat factors appear to be identical based on their reactivity to polyclonal antibody produced against the tumor factor. The factor, assayed by its ability to induce the transport of RNA from isolated nuclei, is a phosphoprotein with a minimum molecular weight of 60,000, as determined by polyacrylamide gel electrophoresis. In its purified form it is phosphorylated in the presence of the catalytic subunit of heart muscle protein kinase and ATP but does not exhibit auto-phosphorylating activity. 32P-orthophosphate is also incorporated into the phosphoprotein in vivo.

Relationship between the transport from isolated nuclei of two abundant cytoplasmic messengers and the source of a messenger RNA transport factor

Messenger RNA transport from isolated nuclei requires a 35 X 10(3) dalton cytoplasmic protein(s) which is present in both the cytosol and polyribosome fractions. Recombinant DNA probes containing cDNA inserts were used to quantitate the transport of rat liver-specific albumin and male rat liver-specific alpha 2U-globulin messenger RNA (mRNA) from male rat liver nuclei in response to the mRNA transport factors from homologous and heterologous tissues. No mRNA transport occurs in the absence of the transport factor(s). Both messengers are transported proportionately in response to the factor(s) from male or female rat liver cytosol, or from the polyribosomes (messenger ribonucleoprotein) of male or female rat liver, or brain. The transport factor(s) do not, therefore, appear to differentiate between the coding sequences of two unrelated hepatic messenger RNA's.

Concurrent changes in growth-related biochemical parameters during regression of hormone-dependent rat mammary tumors

The in vivo relationship was studied between these biochemical parameters which previous studies have separately implicated in the regression of hormone-dependent rat mammary tumors. Upon depletion of estrogen and suppression of prolactin levels by ovariectomy, there was a marked increase in the production of prostaglandin E2 (PGE2)(fourfold) and in the cyclic AMP (cAMP) content (twofold) in the regressing 7,12-dimethylbenz[a]anthracene-induced primary tumors. These two parameters appeared to be coupled since, in addition to this correlation, PGE2 stimulated adenylate cyclase and raised cAMP levels in both this primary tumor system and in another hormone-dependent transplantable rat mammary tumor (MTW9-A). Furthermore both the sensitivity of the adenylate cyclase system to PGE2 and the number of membrane binding sites for PGE2 increased upon induction of regression in these tumors. Under conditions where PGE2 and cAMP were elevated, (i.e., in regressing, but not growing, hormone-dependent mammary tumors), there was significant phosphorylation in the intact tissue of a 75,000-dalton nuclear protein, which appeared to be identical to the regression-associated protein shown by Cho-Chung and co-workers to undergo increased phosphorylation in response to elevated cAMP levels.

An oncofetal 60-kilodalton protein in the plasma of tumor-bearing and carcinogen-treated rats

A Mr 60,000 protein, detected by its ability to induce the release of RNA from isolated nuclei, is present in the plasma of tumor-bearing and carcinogen-treated rats, together with low amounts of 2 messenger RNA transport proteins identified earlier in normal cells. The Mr 60,000 protein has been identified in tumor cell cytoplasm and in amniotic fluid, but does not appear to cross the placental barrier. Significant amounts of the Mr 60,000 oncofetal protein appear in the plasma of carcinogen-treated rats within a few weeks of treatment. It may be the fetal form of the adult messenger RNA transport proteins.

Characterization of a messenger RNA transport protein

A cytoplasmic protein which facilitates the energy-dependent transport of mRNA from isolated nuclei to a specified medium has been further characterized, since it could have relevance to the mechanism of mRNA nucleo-cytoplasmic transport in vivo. This protein is now shown, by cDNA hybridization analysis using appropriate recombinant probes, to be obligatory for the transport of alpha 2u-globulin and albumin mRNA from male rat liver nuclei. It is concentrated in the cytoplasm. When isolated under conditions where they retain nuclear proteins, the nuclei contain less than 2% of the total mRNA transport activity. Approx. 20% is recovered in the cytosol, while the rest (80%) copurifies with the messenger ribonucleoproteins in the polyribosome fraction. The protein is eluted from the poly A-messenger ribonucleoproteins between 0.25 and 0.50 M NaCl. The activities of the cytosolic- and messenger ribonucleoprotein-derived transport proteins were mutually additive below saturation of the transport system. Further, the activities of both fractions were increased when they were fortified with the catalytic subunit of the cAMP-dependent protein kinase in the presence of ATP. On the other hand, protein kinase-induced thiophosphorylation of the protein with ATP[S] decreased transport activity. The molecular weight of the transport protein from either cell compartment as judged by molecular sieving is approx. 35,000. It has now been purified 2000-fold and requires manganese ions and serum albumin for stabilization of activity. The highly purified transport factor from the cytosol is tentatively assigned a molecular weight of 32,000 by SDS-polyacrylamide gel electrophoresis.

Developmental and population commonalities in affective expression: a confirmatory factor analytic approach

Simultaneous factor analysis of interview data from 1,641 respondents confirms a structural model for the expression of affectivity which appears to generalize across ages of both children and adolescents and across normal and psychopathological populations. The four-dimensional solution obtained here suggests that factors associated with deviations in feeling, relating, thinking, and impetuosity may represent stable attributes measurable from the Structured Pediatric Psychosocial Interview.

Messenger RNA populations and their nuclear precursors in cultured human glioma and fetal brain cells

Using labelled single copy DNA to cytoplasmic messenger RNA from a glioma cell line, it is shown by the excess RNA hybridization technique that a human glioma and a human fetal brain cell line both contain the mid and low abundancy classes of cytoplasmic messenger RNA. However, the high abundancy class present in the glioma cells is absent from the hybridization profile of the fetal cell line. Most of the nuclear RNA species complementary to this single copy DNA were present in the low abundancy class of both cell types; the mid-abundancy class was present in much lower concentration than in glioma cytoplasmic RNA and the high abundancy class was essentially absent. The extent of formation of S1-nuclease resistant hybrids indicated that some of the messengers which are present in the high abundancy class in the cytoplasm of glioma cells are present in the lower abundancy classes of fetal brain cells. Thus the glioma cells appear to exhibit a higher degree of specialization potential than the embryonic cells.

Effect of physiological concentrations of insulin and antidiabetic drugs on RNA release from isolated liver nuclei

The addition of 10(-11) M insulin to a cell-free system from rat liver promotes the release of messengerlike RNA from isolated prelabeled nuclei. The stimulation was similar whether the nuclei were preincubated with insulin, or if insulin was added directly to the cell-free system with or without a protease inhibitor. Dot blot hybridization using cloned cDNA for alpha 2u-globulin mRNA showed that this was one of the messages whose release was enhanced by insulin. Nuclei isolated from rats treated with either of the antidiabetics tolbutamide or tolazamide showed no increase in RNA release in the presence of insulin over the concentration range 10(-5) - 10(-14) M. Furthermore, these nuclei did not release detectable levels of alpha 2u-globulin mRNA.