Margaret Hanausek-Walaszek

Changes in nuclear RNA transport incident to carcinogenesis

Abstract Rats were treated with the hepatocarcinogens thioacetamide and dimethylnitrosamine and the release (transport) of RNA from the isolated liver nuclei to homologous or heterologous liver cytosol was evaluated in a cell-free system at various times after treatment. Within 24 hr of treatment, cytosol from the carcinogen-treated animals enhanced the release of RNA from liver nuclei of untreated rats. This enhanced transport capacity of the cytosol persisted up to 4 months after treatment; furthermore, the RNA transport from the liver nuclei of carcinogen-treated animals showed a partial loss of its ATP-dependence. Although the capacity of cytosol from treated animals to support RNA transport dropped below control levels by 9 months after treatment, the RNA transport from nuclei of the carcinogen-treated animals remained partially ATP-independent. This ATP-independence, which is also a characteristic of nuclei from hepatomas, is not a characteristic of the age of the animal, nor is it due to differences in the pool size of nuclear ATP or the requirement for polyadenylation of messenger RNA for transport.

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.

Repression by sustained-release β-glucuronidase inhibitors of chemical carcinogen-mediated induction of a marker oncofetal protein in rodents

The degree of induction of an oncofetal protein marker in rodents by selected chemical carcinogens has been correlated with changes in carcinogenicity induced by dietary D-glucaro-1,4-lactone (GL) based anticarcinogens. These potent anticarcinogens may act to increase the clearance of carcinogens as glucuronides through the inhibition of beta-glucuronidase. The sustained-release forms are particularly effective, 1.5 mmol/kg of GL maintaining serum beta-glucuronidase activity at or below 50% for only 1 h, while an equivalent amount of calcium glucarate (CGT) maintained this level of inhibition for over 5 h. CGT or other sustained-release inhibitors, when fed to rodents during administration of carcinogens that undergo glucuronidation, caused a marked reduction in the induction of the marker protein. For those systems where other markers of carcinogenesis were also assessed, it was determined that the inhibition of marker-protein induction was quantitatively similar to both the inhibition of binding of the carcinogen to DNA and the subsequent induction of tumors in target organs.

β-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 β-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 β-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 β-glucuronidase activity. In one group the activity was near normal, while in the second group the average serum β-glucuronidase activity was 3-fold higher than in the women who did not have benign breast disease.

The repression and derepression of hepatic tyrosine aminotransferase by carcinogens.

Like hydrocortisone, a single carcinogenic dose of dimethylnitrosamine (50 mg/kg) initiates the induction cycle for hepatic tyrosine aminotransferase in adrenalectomized rats. However, following this initial induction in the presence of dimethylnitrosamine, the enzyme becomes refractory to reinduction by known inducers. The administration of thioacetamide to either adrenalectomized or intact rats leads to an immediate and progressive loss of inducibility by hydrocortisone, dibutyrylcyclic AMP or dimethylnitrosamine. Although the thioacetamide-induced repression was not reversed even up to 10 weekds after the cessation of treatment, it was reversed after the induction of liver regeneration. Both the carcinogen-mediated induction and repression of tyrosine aminotransferase appears to occur by mechanisms which do not involve the corticosteroid-binding proteins which normally mediate the induction by glucocorticoids.