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

Abstract

Actinomycin D, an inhibitor of DNA-dependent RNA synthesis, increased the hepatic concentration of a2u globulin, an androgen-inducible protein in the rat. Spayed female rats with a marginally induced state of a2u synthesis showed an approximately 5-fold increase in hepatic a2u globulin within 3-6 hr after treatment with actinomycin D. Initial treatment of these animals with 5a-dihydrotestosterone, followed by actinomycin D, resulted within 2-3 hr in a more than 2-fold increase in hepatic a2u 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 a2u globulin. These results showing increase in both a2u globulin and its translatable mRNA after superinduction with actinomycin D support the concept of post-transcriptional repression of a2u synthesis. Actinomycin D, an inhibitor of DNA-dependent RNA synthesis, increases the level of several inducible proteins, a phenomenon termed "superinduction" (1, 2). Because actinomycin D inhibits mRNA synthesis, superinduction by this drug indicates an apparent paradox, the resolution of which may provide important clues concerning the mechanism of gene regulation in the eukaryotic cell. In fact, the post-transcriptional model for the steroidal regulation of gene activity, proposed by Tomkins and coworkers, is based primarily on their interpretation of the superinduction of glucocorticoid-mediated synthesis of tyrosine aminotransferase (TAT) by actinomycin D in hepatoma cells and in rat liver (3). A similar model of translational repression was also suggested by McAuslan (4). The above investigators have proposed that the mRNAs for the inducible proteins are continually being synthesized within the permissive phase of the cell cycle. However, the simultaneous presence of rapidly turning over post-transcriptional repressors prevents the translation of these mRNAs and may lead to their degradation. It is also proposed that, in the presence of inducing steroids, the repressor is inactivated and, because of its short half-life, is preferentially eliminated by actinomycin D, both of which phenomena would favor an accumulation of the inducible mRNA leading to increased synthesis of the inducible protein (3). Due to technical limitations, experimental verification of the McAuslan-Tomkins model has been difficult, and various other interpretations for the phenomenon of superinduction by actinomycin D have been proposed (5-7).In our laboratory we have developed a model system for the study of hormone action in rat liver (8, 9). The system involves androgen-dependent synthesis of a low molecular weight (23,000) protein called a2u globulin (10, 11). We have also identified the mRNA for a2u globulin in rat liver and have established a strong correlation between the androgen-dependent increase in a2u synthesis and the hepatic concentration of the mRNA for this protein (9,12,13 Cyclohexim...

Regulation of cadmium(2+)/zinc(2+)-stimulated metallothionein synthesis during induction, deinduction, and superinduction

“…Additional experiments with AM provided evidence for AM-mediated superinduction of metal-induced MT synthesis analogous to effects of AM reported in other inducible systems (Tomkins et al, 1969(Tomkins et al, , 1972Steinberg et al, 1975a;Chatterjee et al, 1979). When 2 µg/mL AM is added to maximally induced Cdr cells (2µ Cd2+ for 8 h; Figure 5A), the MT synthesis rate is increased significantly relative to that in the AM-free control cells.…”

“…Although a considerable controversy has surrounded quantitative interpretation of the results of some applications of this inhibitor (cf. Chatterjee et al, 1979), the use of AM to inhibit general RNA synthesis or nucleolar RNA synthesis, specifically, has proven fruitful in numerous studies and has been applied extensively in the investigation of inducible systems (Tomkins et al, 1972;Killewich et al, 1975;Steinberg et al, 1975a;Chatterjee et al, 1979). In the present study, it was found (Table I) that induction of MT synthesis is inhibited not only by a high level of AM (2.0-5.0 µg/mL), which blocks all RNA synthesis, but also by a low level of AM (0.05 gg/mL), which preferentially inhibits nucleolar RNA synthesis (Perry & Kelly, 1970).…”

Hazard Evaluation of Chemicals That Cause Accumulation of α 2u -Globulin, Hyaline Droplet Nephropathy, and Tubule Neoplasia in the Kidneys of Male Rats

“…Neither ca2u-g nor its corresponding mRNA is detectable in the livers ofsexually intact female rats (69,74,75). However, a very low background level ofthe mRNA has been indicated in the ovariectomized female rat (76), and ovariectomy in concert with androgen treatment induces a parallel increase in a2u-g and its mRNA in female rat liver (67,74).…”

DNA Damage and Chromatin Conformation Changes Confer Nonhost Resistance: A Hypothesis Based on Effects of Anti-cancer Agents on Plant Defense Responses

“…As indicated earlier, extensive research on the DNA-specific intercalator actinomycin D indicates the diversity of action in vivo . Actinomycin D was found to be a super inducer of the synthesis of some animal genes ( Chatterjee et al, 1979 ). In an early screening of intercalators, we found actinomycin D and other intercalators to be strong activators of plant defense responses ( Schwochau and Hadwiger, 1968 ).…”