By means of RNAase protection assay with an antisense cRNA probe, we have shown that the liver of the young adult male rat contains androgen receptor (AR) mRNA to a level of 4% compared to the prostate. Steady state levels of AR mRNA in the liver show both sex and age specificity. Compared to that of the male, the female liver contains a markedly reduced amount of AR mRNA. AR mRNA is almost undetectable in livers of prepubertal male (less than 35 days old) and senescent male (greater than 750 days old) rats. Both prepubertal and senescent animals are relatively insensitive to the androgenic induction of alpha 2u-globulin, a hepatic secretory protein. The age-dependent decline in hepatic androgen sensitivity and AR mRNA level can be delayed considerably by a 40% reduction in the dietary calorie intake. Analysis of poly(A)-containing RNA from two liver cell populations, hepatocytes and nonhepatocytes, revealed that only the hepatocytes that express alpha 2u-globulin gene contain AR mRNA. From these results and our earlier observation of in vitro induction of alpha 2u-globulin in isolated rat liver, we conclude 1) that androgen can act directly on hepatocytes to promote alpha 2u-globulin synthesis; 2) that changes in the hepatic androgen sensitivity during maturation and aging are reflections of the age-dependent expression of the receptor gene; and 3) that retardation of the age-dependent loss of androgen sensitivity by calorie restriction is due to a concomitant delay in the decline of the hepatic AR mRNA level.

When Friend erythroleukemia cells were allowed to grow to stationary phase (2 X 10(6) to 3 X 10(6) cells per ml), approximately 60% of the mRNA for eucaryotic elongation factor Tu (eEF-Tu) sedimented at less than or equal to 80S, and most of the remaining factor mRNA was associated with small polysomes. Under the same growth conditions, greater than 90% of the mRNA for eucaryotic initiation factor 4A remained associated with polysomes. The association of eEF-Tu mRNA with polysomes changed dramatically when stationary-phase cells were treated with fresh medium. After 1 h in fresh medium, approximately 90% of eEF-Tu mRNA in Friend cells was found in heavy polysomes. Associated with the shift of eEF-Tu mRNA into heavy polysomes, we found at least a 2.6-fold increase in the synthesis of eEF-Tu in vivo as well as a remarkable 40% decrease in the total amount of eEF-Tu mRNA per cell. Our data raise the possibility that eEF-Tu mRNA that has accumulated in ribonucleoprotein particles in stationary-phase cells is degraded rather than reutilized for eEF-Tu synthesis.

Mammalian estrogen sulfotransferase (EST; EC 2.8.2.4) sulfurylates the hydroxyl group of estrogenic steroids by transferring the sulfate from a cosubstrate adenosine 3'-phosphate-5'-phosphosulfate. Sulfurylated steroids do not bind to the estrogen receptor with high affinity and, therefore, are hormonally inactive. We have purified rat liver EST and developed monoclonal antibody to this enzyme. By immunoscreening a lambda gt-11 expression library constructed from male rat liver cDNAs, the cDNA clone corresponding to EST was identified and isolated. A recombinant expression plasmid (pCMV5) containing this cDNA insert when transfected into COS-7 cells generated both immunologically and enzymatically active EST. With the help of this cDNA probe, we have explored the regulation of the EST mRNA in the liver and the possible role of this enzyme in sex hormone action. During the lifespan of male rats, only the young adult animals show hepatic androgen responsiveness. Also, estrogenic hormones strongly antagonize androgen action in the rat liver. Northern blot analysis of liver RNA derived from male rats of different ages shows that the androgen sensitivity of young adult animals is associated with a high expression of EST mRNA. During the same period, mRNA corresponding to dehydroepiandrosterone sulfotransferase is markedly (approximately 10-fold) down-regulated. Such a correlation is in concordance with the role of these enzymes in the maintenance of hepatic androgen sensitivity during young adult life by inactivating the estrogenic and sparing the androgenic steroids. Furthermore, the increase in the hepatic androgen sensitivity of androgen-treated female rats is also associated with the induction of EST.(ABSTRACT TRUNCATED AT 250 WORDS)

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The decay rates of eucaryotic elongation factor Tu (eEF-Tu) mRNA and eucaryotic initiation factor 4A (eIF-4A) mRNA in Friend erythroleukemia (FEL) cells were determined under several different growth conditions. In FEL cells which were no longer actively dividing (stationary phase), eEF-Tu mRNA was found to be rather stable, with a tl2 of about 24 h. In rapidly growing FEL cells eEF-Tu mRNA was considerably less stable, with a t4/2 of about 9 h. In both cases a single rate of mRNA decay was observed. However, when stationary-phase cells resumed growth after treatment with fresh medium, we observed that eEF-Tu mRNA decay followed a biphasic process. The faster of the two decay rates involved approximately 50% of the eEF-Tu mRNA and had a tl2 of about 1 h. The decay rates for eIF-4A (tl/2 = 2 h) and total poly(A)+ RNA (tl2 = 3 h) were unaffected by changes in growth conditions. The 4,2 for polysomal eEF-Tu mRNA was found to be about 8 h when stationary FEL cells were treated with fresh medium. Previous work in this laboratory has shown (T. R. Rao and L. I. Slobin, Mol. Cell. Biol. 7:687-697, 1987) that when FEL cells are allowed to grow to stationary phase, approximately 60% of the mRNA for eEF-Tu is found in a nontranslating postpolysomal messenger ribonucleoprotein (mRNP) particle. eEF-Tu mRNP was rapidly cleared from stationary cells after treatment with fresh medium. The data presented in this report indicate that the stability of eEF-Tu mRNP is rapidly altered and the particle is targeted for degradation when stationary FEL cells resume growth.Of the processes which regulate the expression of genes, the ones which determine the stability of mRNA in the cytoplasm of cells are among the least well understood. In general, individual eucaryotic mRNAs have characteristic rates of decay within a given cell type, with different mRNAs having widely different stabilities. It has also become apparent that many mRNAs have variable rates of decay under different physiological conditions (37). For example, the stability of histone mRNAs changes during the cell cycle (19), and the stability of numerous mRNAs is influenced by treatment of sensitive cells with the appropriate hormones (4,5,17). Recent studies have implicated both the 5' leader region and the 3' untranslated sequence of certain mRNAs as targets for the initiation of the mRNA decay process (3,16,26,38). However, other factors besides sequence must be important in regulating mRNA stability if the half-life of a given mRNA is variable within a given cell type.The necessity of accounting for variability in mRNA half-life has led several investigators to consider the possible role of the translational process in the regulation of mRNA stability. Two types of regulation have been suggested on the basis of the use of different inhibitors of protein synthesis. For example, both cycloheximide (an elongation inhibitor) and pactamycin (an initiation inhibitor) were found to stabilize histone mRNA when DNA replication was blocked (39) and to stabilize c-myc mRNA (26). Th...