Arun K. Roy

Androgen receptor in rat liver: Hormonal and developmental regulation of the cytoplasmic receptor and its correlation with the androgen-dependent synthesis of α2u-globulin

The cytoplasmic receptor for 5α-dihydrotestosterone has been identified in the rat liver and partially characterized. The receptor is a protein with a sedimentation coefficient of 3.5 S and binds both androgens (5α-dihydrotestosterone and testosterone) and estradiol-17β with high affinity. At saturating concentration, for every mole of estradiol there seem to be three moles of 5α-dihydrotestosterone bound to the receptor. Whereas estradiol stronly inhibits the uptake of 5α-dihydrotestosterone by the receptor, the presence of 5α-dihydrotestosterone only weakly interferes with estradiol binding. n nThe level of the androgen receptor activity in the hepatic cytosol was found to follow closely the level of the urinary output of α-2u-globulin, an androgen-dependent protein of hepatic origin. Immature and senile male as well as female rats, which do not normally produce α2u-globulin, also lacked androgen receptor activity in their hepatic cytosol. Castration of the adult male rats results in a gradual drop of the urinary output of α2u-globulin as well as of the hepatic androgen receptor activity. Androgen treatment of immature and senile male rats does not induce α2u-globulin or any receptor activity. Administration of estradiol to adult male rates results in complete inhibition of both α2u-synthesis as well as complete loss of the cytosol androgen receptor activity in these animals. These results strongly indicate that the hepatic the hepatic androgen receptor activity. Androgen treatment of immature and senile male rats does not induce α2u-globulin or any receptor activity. Administration of estradiol to adult male rats results in complete inhibition of boty α2u-synthesis as well as complete loss of the cytosol androgen receptor activity in these animals. These results strongly indicate that the hepatic androgen receptor is an inducible protein whose synthesis is regulated by its own ligands, the androgens acting as the positive and the estradiol as the negative signals.

Accumulation of α2u-globulin in the renal proximal tubules of male rats exposed to unleaded gasoline

Saturated branched-chain aliphatic hydrocarbons, found in motor fuels, induce nephrotoxicity in male rats. Treatment of male rats with unleaded gasoline (0.04-2.0 ml/kg body wt, po) for 9 days increased markedly the number and size of hyaline (protein resorption) droplets in epithelial cells of the renal proximal convoluted tubules (PCT) and enhanced cellular exfoliation at high dose levels. No other treatment-related pathological effects were observed in the glomeruli, distal tubules, or medulla. The renal content of alpha 2u-globulin, a major urinary protein of male rats, was increased maximally by about 4.4-fold after gasoline administration (1.0 ml/kg, po, 9 days); no further increase was observed at higher doses. Immunoperoxidase staining of kidney tissue sections for alpha 2u-globulin revealed large accumulations of antigen localized in many of the PCT epithelial cells which contained hyaline droplets. The hepatic content of alpha 2u-globulin and its mRNA were not altered by gasoline administration. These data show, for the first time, that alpha 2u-globulin is accumulated in the kidneys of gasoline-intoxicated male rats and sequestered specifically in some of the hyaline droplets characteristic of gasoline-induced nephropathy. A hydrocarbon-induced defect in the renal lysosomal degradation of low-molecular-weight urinary proteins, rather than increased synthesis of these proteins, appears to cause hyaline droplet accumulation.

Hormone and age-dependent regulation of alpha 2u-globulin gene expression.

Publisher Summary This chapter discusses the hormone and age-dependent regulation of α 2u- globulin gene expression. α 2u -globulin is the major urinary protein of the mature male rat. Rats and other rodents show an unusually high degree of proteinuria. About 50% of the total urinary proteins can be accounted for by one immunochemically distinct protein moiety with the same electrophoretic mobility as α 2 -globulin of rat serum. This urinary α 2 -globulin is different from the serum α 2 -globulin and hence this protein is named α 2u -globulin with the subscript “u” to signify its abundance in the urine. Subsequent studies have shown that α 2u -globulin is synthesized and secreted by the hepatic parenchymal cells. Because of its relatively low molecular weight, it is rapidly filtered through the kidneys where in one pass only about 15% is recycled into the plasma and the rest is excreted into the urine, and as a result, the plasma concentration of α 2u -globulin remains very low. In addition to liver and kidney, immunochemical analyses of various other tissues have shown the presence of α 2u -globulin in the salivary gland. Translational analyses in the heterologous cell free system and in Xenopus oocytes and hybridizational assay with a cloned complimentary DNA (cDNA) probe have shown that steroid hormones, insulin, and growth hormone regulate hepatic synthesis of α 2u -globulin through changes in the hepatic concentration of the mRNA for this protein. The effects of thyroidectomy and thyroxine supplementation on α 2u -globulin synthesis are also reflected by corresponding changes in the hepatic concentration of α 2u -globulin messenger RNA (mRNA).

Regulation of the hepatic synthesis of α2u globulin and its corresponding messenger RNA in maturing male rats

cx2u globulin is the principal urinary protein in the mature male rat [ 1,2] . The protein has been shown to be synthesized and secreted by the hepatic parenchymal cells [3,4]. Studies on the action of various hormones on 02u y s nthesis have shown that androgens, thyroid hormones, glucocorticoids, pituitary growth hormone and insulin promote, whereas estrogen treatment completely suppresses the synthesis of this protein [5-IO] . ‘~2” globulin could be induced in the mature female rat after ovariectomy followed by androgen treatment [5]. Results obtained with various model systems involving reproductive tissues have provided strong support for the concept that circulating steroid hormones regulate cell function by modulating the synthesis of cellular RNA and especially the synthesis of specific messenger RNA [l l-181. However, alternative possibilities such as post-transcriptional and translational regulation of protein synthesis by steroid hormones have not been completely ruled out [ 19,201. Our earlier studies have shown that androgen treatment of spayed rats results in the induction of both cu2u globulin and its corresponding messenger RNA in the liver [21]. All of the above studies on the steroidal control of gene regulation have been limited to effects of hormone treatment or hormone withdrawal in the experimental system and, to our knowledge, changes in the levels of specific mRNA activity under physiological variations of the steroid hormones have not been investigated. Therefore, in order to expand our knowledge of the mechanism of the androgenic regulation of 02U synthesis and to study the role of physiological variations of the

Leupeptin-mediated alteration of renal phagolysosomes: similarity to hyaline droplet nephropathy of male rats exposed to unleaded gasoline

alpha 2u-Globulin, a protein of hepatic origin found in the urine of male rats, is accumulated in the kidney cortex during exposure to unleaded gasoline and has been implicated in the development of fuel hydrocarbon-induced nephropathy and renal neoplasia. The principal morphological feature of gasoline-induced nephropathy is accumulation of hyaline droplets (enlarged secondary lysosomes or phagolysosomes) in epithelial cells of the proximal convoluted tubule S1 and S2 segments. Inhibition of cathepsin B (a major lysosomal peptidase) by treatment of male rats with leupeptin causes rapid accumulation of phagolysosomes and alpha 2u-globulin in the kidney very similar to gasoline exposure. Further, the renal cortical subcellular distribution of alpha 2u-globulin, determined with an electron microscopic immunochemical method, is almost totally confined to phagolysosomes following administration of either gasoline or leupeptin. These results, taken together, indicate that the mechanism of nephrotoxicity of gasoline involves inhibition of renal phagolysosomal proteolysis.

Rapid Post-Exposure Decay of a_2u -Globulin and Hyaline Droplets in the Kidneys of Gasoline-Treated Male Rats

Unleaded gasoline induces nephropathy, characterized by rapid accumulation of hyaline (protein resorption) droplets in epithelial cells of the renal proximal convoluted tubules, only in male rats. The hepatic synthesis of the male rat-specific protein alpha 2u-globulin, a constituent of renal hyaline droplets, is unaltered by gasoline treatment (Olson et al., 1987). Renal alpha 2u-globulin content increased to 210% of control within 18 h of a single oral dose of gasoline (2.0 ml/kg); maximal levels (320% of control) were attained following gasoline administration for 3 d. Increases in renal alpha 2u-globulin caused by gasoline were accompanied by concurrent proliferation of hyaline droplets. However, within 3 d of terminating gasoline administration renal alpha 2u-globulin content decreased to the same level as that in unexposed rats, although renal hyaline droplet number returned to pretreatment levels somewhat more slowly. The conjoint effect of postexposure recovery and estradiol (an inhibitor of hepatic alpha 2u-globulin synthesis) administration was also determined in male rats. On postexposure d 3, 6, and 9, estradiol treatment (1 mg/kg, sc, 4 d, starting on d 9 of gasoline treatment) decreased renal alpha 2u-globulin content to 75%, 59%, and 48%, respectively, of that in rats allowed to recover from gasoline with no hormone treatment. Hepatic alpha 2u-globulin content in estradiol-treated rats was decreased by 74%, 97%, and 96% at the same intervals. Estradiol treatment during recovery from gasoline also appeared to increase the removal of accumulated hyaline droplets from the renal cortex. Thus, accumulation of alpha 2u-globulin-containing hyaline droplets after subacute exposure of male rats to gasoline is rapidly reversible, dependent on continuous exposure to gasoline and maintenance of the normal rate of hepatic alpha 2u-globulin synthesis. These results emphasize the dynamic state of renal cortical hyaline droplets and suggest strongly that gasoline hydrocarbons cause hyaline droplet accumulation by prolonging the half-time of degradation of alpha 2u-globulin.

Inhibition of the alanine tRNA aminoacylation by Ca2

Abstract The effect of Ca 2+ concentration on the in vitro aminoacylation of Escherichia coli tRNAs was tested. At a Ca 2+ concentration of 0.5 mM the aminoacylation of only two tRNAs, rRNA Ala and tRNA Cys , were found to be inhibited by 56% and 18%, respectively. The aminoacylation of tRNA Ala was completely inhibited at 5 mM Ca 2+ . The relatively high sensitivity of the aminoacylation of tRNA Ala to such a low level of Ca 2+ might suggest physiological role of Ca 2+ in the control of protein synthesis.

Androgenic repression of the messenger RNA for a 26.3-kDa hepatic protein in the rat

not received Androgenic repression Hormone action Steroid hormone