Genetic regulation of mammalian glucuronidase

Androgen responsiveness of the murine beta-glucuronidase gene is associated with nuclease hypersensitivity, protein binding, and haplotype-specific sequence diversity within intron 9

The tissue specificity and genetic variability of the murine beta-glucuronidase (GUS) response to androgen provide useful markers for identifying elements which underlie this responsiveness. While GUS is expressed constitutively in all examined cell types, kidney epithelial cells uniquely exhibit a manyfold yet slow rise in GUS mRNA and enzyme levels when stimulated by androgens. Three major phenotypes of this androgen response have been described among inbred strains of mice: (i) a strong response in strains of the Gusa haplotype, (ii) a reduced response in strains of the Gusb and Gush haplotypes, and (iii) no response, as observed in Gusor mice. These response variants define a cis-active element(s) which is tightly linked to the GUS structural gene. Nuclease hypersensitivity scans of kidney chromatin within and surrounding the structural gene revealed an androgen-inducible hypersensitive site in intron 9 of the gene in Gusa but not in Gusor mice. When a radiolabeled fragment of Gusa DNA containing this hypersensitive site was incubated with kidney nuclear extracts and then subjected to gel electrophoresis, two shifted bands were observed whose levels were dramatically higher in extracts of androgen-treated than in those of untreated Gusa mice. The shifted bands reflect binding of a kidney-specific factor(s) to a 57-bp region of complex dyad symmetry in Gusa and Gusor mice which is partially deleted in Gusb and Gush mice. This binding site is located approximately 130 bp downstream of a glucocorticoid response element sequence motif which is totally deleted in [Gus]or mice. Taken together, our results suggest that the androgen responsiveness of GUS in murine kidney epithelial cells is controlled by elements within the proximal end of intron 9 of the GUS structural gene.

Androgen responsiveness of the murine beta-glucuronidase gene is associated with nuclease hypersensitivity, protein binding, and haplotype-specific sequence diversity within intron 9

The tissue specificity and genetic variability of the murine beta-glucuronidase (GUS) response to androgen provide useful markers for identifying elements which underlie this responsiveness. While GUS is expressed constitutively in all examined cell types, kidney epithelial cells uniquely exhibit a manyfold yet slow rise in GUS mRNA and enzyme levels when stimulated by androgens. Three major phenotypes of this androgen response have been described among inbred strains of mice: (i) a strong response in strains of the Gusa haplotype, (ii) a reduced response in strains of the Gusb and Gush haplotypes, and (iii) no response, as observed in Gusor mice. These response variants define a cis-active element(s) which is tightly linked to the GUS structural gene. Nuclease hypersensitivity scans of kidney chromatin within and surrounding the structural gene revealed an androgen-inducible hypersensitive site in intron 9 of the gene in Gusa but not in Gusor mice. When a radiolabeled fragment of Gusa DNA containing this hypersensitive site was incubated with kidney nuclear extracts and then subjected to gel electrophoresis, two shifted bands were observed whose levels were dramatically higher in extracts of androgen-treated than in those of untreated Gusa mice. The shifted bands reflect binding of a kidney-specific factor(s) to a 57-bp region of complex dyad symmetry in Gusa and Gusor mice which is partially deleted in Gusb and Gush mice. This binding site is located approximately 130 bp downstream of a glucocorticoid response element sequence motif which is totally deleted in [Gus]or mice. Taken together, our results suggest that the androgen responsiveness of GUS in murine kidney epithelial cells is controlled by elements within the proximal end of intron 9 of the GUS structural gene.

Androgen regulation of rat renal angiotensinogen messenger RNA expression

Renal angiotensinogen (ang-n) mRNA concentration in the male WKY rat increases significantly during puberty. Furthermore, renal angiotensinogen mRNA level in the adult female WKY rat is considerably lower than in the male. The present study investigates the role of androgen in differential renal ang-n mRNA expression. Northern and slot blot analyses with alpha-32P labeled ang-n cDNA (pRang 3) demonstrated that castration lowered ang-n mRNA levels in the male kidney by greater than or equal to 60% compared with control, suggesting that androgen may be involved with renal ang-n gene regulation. Moreover, male WKY rats castrated as weanlings and normal adult female WKY rats each implanted with testosterone displayed significant (P less than 0.05) increases in renal ang-n mRNA levels. Our observations, taken together with previous reports that androgen influences proximal tubule morphology and the tubular expression of transport proteins (e.g., Na+/H+ antiporter), may have important physiological implications for understanding the relationship between androgen and angiotensin in the regulation of tubular function.

Genomic organization and sequence of the Gus-s alpha allele of the murine beta-glucuronidase gene

The Gus-s alpha allele of the mouse beta-glucuronidase gene exhibits a high degree of inducibility by androgens due to its linkage with the Gus-r alpha regulatory locus. We isolated Gus-s alpha on a 28-kilobase pair fragment of mouse chromosome 5 and found that it contains 12 exons and 11 intervening sequences spanning 14 kilobase pairs of this genomic segment. The mRNA cap site was identified by ribonuclease protection and primer extension analyses which revealed an unusually short 5' noncoding sequence of 12 nucleotides. Proximal regulatory sequences in the 5'-flanking DNA and the complete sequence of the Gus-s alpha mRNA transcript were also determined. Comparison of the amino acid sequence determined from the Gus-s alpha nucleotide sequence with that of human beta-glucuronidase indicated that the two human mRNA species differ due to alternate splicing of an exon homologous to exon 6 of the mouse gene.

Androgen regulation of murine beta-glucuronidase expression: identification and characterization of a nonresponse variant

One of the major features of beta-glucuronidase (GUS) expression in inbred strains of the house mouse, Mus musculus, is the responsiveness of this enzyme to androgen stimulation in tubule cells of the kidney. Both GUS-specific and nonspecific mutations have been described which define genes that serve to control this response. During examination of the expression of GUS in the interbreeding subspecies, Mus hortulanus, a new GUS haplotype was uncovered that is characterized, in part, by a lack of GUS response to androgen stimulation in an apparently responsive kidney. Blot hybridization analyses of kidney RNA with a radiolabeled murine GUS cDNA shows this lack of response to be reflected in GUS mRNA levels. The difference in heat stability of GUS activity between M. hortulanus and a responsive inbred strain, ICR/Ha, was utilized to assess the contribution of each parent to kidney levels of GUS in androgen-treated and -untreated F1 progeny of these strains. The results, together with preliminary genetic studies, suggest that the element controlling this responsiveness (or the lack thereof) is cis-active and tightly linked to the GUS structural gene on chromosome 5. It is not known whether this element is identical to another GUS-specific, cis-active element, Gus-r, which also controls the androgen response of GUS in mouse kidney.

Genomic organization and sequence of the Gus-s alpha allele of the murine beta-glucuronidase gene

The Gus-s alpha allele of the mouse beta-glucuronidase gene exhibits a high degree of inducibility by androgens due to its linkage with the Gus-r alpha regulatory locus. We isolated Gus-s alpha on a 28-kilobase pair fragment of mouse chromosome 5 and found that it contains 12 exons and 11 intervening sequences spanning 14 kilobase pairs of this genomic segment. The mRNA cap site was identified by ribonuclease protection and primer extension analyses which revealed an unusually short 5' noncoding sequence of 12 nucleotides. Proximal regulatory sequences in the 5'-flanking DNA and the complete sequence of the Gus-s alpha mRNA transcript were also determined. Comparison of the amino acid sequence determined from the Gus-s alpha nucleotide sequence with that of human beta-glucuronidase indicated that the two human mRNA species differ due to alternate splicing of an exon homologous to exon 6 of the mouse gene.

Biochemical and morphological characterization of primary kidney cell cultures from beige mutant mice

Primary kidney cultures from adult beige-J (bgJ/bgJ) mice were selected for epithelial cell growth using D-valine medium. After 2 weeks of attachment and proliferation in vitro, the cells form a confluent or nearly confluent monolayer that retains several phenotypic characteristics of the beige-J mutant. These include large, multilamellar inclusion bodies that are apparently dysmorphic lysosomes, and higher concentrations of neutral glycosphingolipids and dolichols than control cells. beta-Glucuronidase activity, used as a lysosomal enzyme marker, is not elevated in beige-J-cultured kidney cells compared with controls, as it is in the intact kidney. The high levels of beta-glucuronidase activity in both control and mutant cells may mask expression of this difference in vitro. The action of the beige-J mutation in kidney cells is thought to be due to a block in exocytosis that results in the accumulation of abnormal lysosomes and their components. The maintenance of the beige phenotype in vitro indicates that the mutation is not suppressed in primary kidney cell cultures. The expression of the beige phenotype in vitro should be useful for studies concerning the primary lesion of this mutation.

Lumenal location of the microsomal beta-glucuronidase-egasyn complex

Mouse liver beta-glucuronidase is stabilized within microsomal vesicles by complexation with the accessory protein egasyn. The location of the beta-glucuronidase-egasyn complex and free egasyn within microsomal vesicles was investigated. Surprisingly, it was found that neither the complex nor free egasyn are intrinsic membrane components. Rather, both are either free within the vesicle lumen or only weakly bound to the inside of the vesicle membrane. This conclusion was derived from release studies using low concentrations of Triton X-100 or controlled sonication. Both the intact complex and free egasyn were released in parallel with lumenal proteins, not with intrinsic membrane components. Also, beta-glucuronidase was protected from digestion by proteinase K by the membrane of microsomal vesicles. The hydrophilic nature of both the complex and free egasyn was confirmed by phase separation experiments with the detergent Triton X-114. Egasyn is one of an unusual group of esterases that, despite being located within the lumen or only weakly bound to the lumenal surface of the endoplasmic reticulum, do not enter the secretory pathway.

A regulatory locus, Hdc-e, determines the response of mouse kidney histidine decarboxylase to estrogen

Levels of histidine decarboxylase (HDC; EC 4.1.1.22) activity in female mouse kidney are modulated by estrogen (administered as implanted pellets). In some inbred strains HDC activity is induced by estrogen, while in others the enzyme is repressed. Immunoprecipitation with an anti-fetal rat HDC antiserum has shown that induction and repression of HDC levels are due to changes in enzyme concentration. Segregation analysis has identified a single additively inherited regulatory locus, Hdc-e, which determines the response to estrogen. The allele Hdc-eb (C57BL/10) determines induction, and the allele Hdc-ed (DBA/2) determines repression. Preliminary evidence indicates cosegregation of Hdc-e alleles with alleles of another regulatory locus, Hdc-c (determining kidney HDC concentration), and therefore putative linkage of Hdc-e with the HDC gene complex on chromosome 2. This is the first report of a mammalian regulatory gene controlling two opposite mechanisms, induction and repression in response to a single effector.

Histidine decarboxylase phenotypes of inbred mouse strains: a regulatory locus (Hdc) determines kidney enzyme concentration

Mouse kidney histidine decarboxylase (HDC) provides a model system to study genetic control of a hormone-regulated enzyme (inducible by estrogen and thyroxine; repressible by testosterone). Five major HDC phenotypes scored on the basis of (i) enzyme activity and (ii) the difference in activity between the sexes (females usually higher than males) have been discovered by screening 38 strains of mice. One genetic difference between high-activity strains (DBA/2 and C3H/He) and low-activity strains (C57BL/6 and C57BL/10) has been examined in detail. The phenotypic difference segregates as a single gene in both conventional crosses and between recombinant inbred (RI) strains. Immunoprecipitation has shown that the activity difference is due to an alteration in the number of enzyme molecules. The phenotypic difference between high and low strains can therefore be attributed to different alleles of a single regulatory locus, Hdc; the allele Hdcb determines low HDC concentration, and the allele Hdcd high concentration. Hdc has been mapped to chromosome 2 using data from both comparisons of strain distribution patterns of previously mapped loci within RI strains and a conventional three-point cross. The probable gene order is B2m-pa-Hdc, with map distances of 3.1 +/- 1.7 and 2.0 +/- 1.4 cM, respectively.

DNA sequence polymorphism in an androgen-regulated gene is associated with alteration in the encoded RNAs

We have used plasmid pMK908, whose cDNA insert corresponds to an androgen-inducible RNA from mouse kidney, as a probe to study both the complementary genomic DNA and the encoded RNA sequences in several inbred strains of mice. A polymorphism in the 908 structural gene, revealed by Southern blotting of HindIII-generated DNA fragments, was found to map near the Gpi-1 and Tam-1 loci on chromosome 7. The 908 structural gene has been termed RP2. The 908 RNAs constitute a sequence-related group displaying extensive size heterogeneity. This heterogeneity, reflected in the size distribution of the RNA on electrophoretic blots, is controlled by a genetic site that is tightly linked to RP2. Thus, associated with polymorphism at RP2 is a change in the molecular size pattern of encoded transcripts.

3 alpha, 17 beta-androstanediol glucuronide in plasma. A marker of androgen action in idiopathic hirsutism

Biologically active androgens and peripheral androgen metabolites in plasma were measured in 25 women with idiopathic hirsutism (IH). Plasma testosterone was not significantly elevated. Free testosterone however was increased although the elevation was not impressive (10.9 +/- 6.6 SD vs. 3.3 +/- 1.5 ng/dl) and one-fourth of the cases had normal unbound testosterone. Dihydrotestosterone (DHT) values were elevated (23.5 +/- 14 vs. 12.5 +/- 3.59) but again over half of the values were within the normal range. In our series of mild to moderate cases, 3 alpha-diol was not at all discriminatory. However, plasma 3 alpha-diol glucuronide was markedly increased (604 +/- 376 vs. 40 +/- 10 ng/dl), and elevated in all but one mild case. Previous studies document that DHT is the important androgen in skin and formation of DHT and 3 alpha-diol is markedly increased in vitro in IH. Since 3 alpha-diol glucuronide is derived largely from extrasplanchnic events, beta-glucuronidase is present in skin, and androgen stimulates formation of the enzyme in extrasplanchnic tissue, we conclude that 3 alpha-diol glucuronide is a marker of peripheral androgen action and markedly elevated in IH.

Biosynthesis of the major urinary proteins in mouse liver: a biochemical genetic study

By labeling liver protein in vivo with [3H] leucine, the relative biosynthetic rate has been measured for the major urinary proteins (MUPs), three closely related, androgen-regulated proteins that are synthesized in mouse liver, secreted into the bloodstream, and excreted into the urine. In livers from females of strain C57BL/6J, total MUP synthesis represents about 0.6-0.9% of the total protein synthesis; in males and testosterone-treated females of the same strain, synthesis increases to about 3.5-4.0% of the total. This 4- to 6-fold induction of total MUP synthesis is similar to the androgen-mediated increase in MUP-specific messenger RNA reported by others, and indicates that the previously observed 20- to 25-fold induction of total MUP excretion into urine is generated partly at the posttranslational level. By measuring the ratio of synthesis of the individual MUPs, it was determined that the testosterone-mediated change in the pattern of MUP synthesis, indicating nature, of MUPs excreted. A survey of seven inbred mouse strains revealed polymorphism for the rate of total MUP synthesis in untreated females. Two classes could be distinguished on the basis of a 3-to 5-fold difference in the rate. This variation does not correlate with variation at Mup-a, a locus that controls the ratio of the three MUPs in urine from androgen-induced mice. These findings are consistent with the notion that MUP expression is controlled by a variety of independently assorting genes.

Genetic and endocrine control of renin activity in the submaxillary gland of the mouse

Basal activity of submaxillary gland (SMG) renin is high in female mice that carry the Rnrs allele and is induced to higher levels by treatment with dihydrotestosterone (DHT). To determine whether the difference in basal activity between high (Rnrs/Rnrs) and low (Rnrb/Rnrb) strains is due to enhanced sensitivity of Rnrs/Rnrs strains to endogenous androgen, we first studied the effect of several types of endocrine ablation on SMG renin in young female mice, and second, we removed normal androgen receptor protein by introducing the X-linked Tfm gene. Adrenalectomy with or without castration had no effect on basal SMG renin; hypophysectomy decreased basal renin activity 400-fold but did not abolish responsiveness to DHT. Loss of androgen receptor did not affect basal renin activity but did prevent enhancement by DHT. Basal and induced renin activities in L.AKR(Alll)/Cy, a congenic strain homozygous for Rnrs introduced from AKR/J into the background of C57L/J, an Rnrb/Rnrb type strain, are intermediate between levels observed in the original strains. We conclude that (1) the basal level of SMG renin is regulated directly or indirectly by some pituitary hormone(s) but not by androgen, (2) androgen induction of renin activity requires a normal androgen receptor, and (3) major gene(s) that regulate basal as well as induced SMG renin are in a circumscribed region of chromosome 1.

Intracellular distribution of lysosomal enzymes in the mouse pigment mutants pale ear and pallid

The size distribution of lysosomes was determined in kidney proximal tubule cells of two mouse pigment mutants, pale ear and pallid, which have an increase in kidney lysosomal enzyme content caused by a decreased rate of secretion of lysosomal enzymes into urine. Both mutations have larger lysosomes when compared with normal mice. However, neither mutant contains the giant lysosomes (up to 11 micron diameter) common to the well-characterized beige mutant, which has a kidney secretory defect similar to the pale ear and pallid mutants. Subcellular distribution studies, performed by the osmotic shock technique, likewise suggested differences among the pigment mutants. A very high content of soluble enzyme, indicative of lysosomal fragility during homogenization, was found in extracts from the beige mutation. By comparation, the percent of soluble enzyme became progressively lower in extracts of the pallid and pale ear mutants and was lowest in extracts from normal mice. All 3 pigment mutants had normal concentrations of osmotically resistant membrane-bound lysosomal enzymes. This indicates that the excess, non-secreted, lysosomal enzyme in all three pigment mutants likely is present in classical lysosomal organelles rather than in other non-lysosomal subcellular membrane fractions. The results also illustrate that mammalian mutants which exhibit lysosomal secretory rates can have strikingly different effects on morphology of lysosomes.