Molecular genetics of androgen-inducible RP2 gene transcription in the mouse kidney

Nudt19 is a renal CoA diphosphohydrolase with biochemical and regulatory properties that are distinct from the hepatic Nudt7 isoform

CoA is the major acyl carrier in mammals and a key cofactor in energy metabolism. Dynamic regulation of CoA in different tissues and organs supports metabolic flexibility. Two mammalian Nudix hydrolases, Nudt19 and Nudt7, degrade CoA in vitro Nudt19 and Nudt7 possess conserved Nudix and CoA signature sequences and specifically hydrolyze the diphosphate bond of free CoA and acyl-CoAs to form 3',5'-ADP and 4'-(acyl)phosphopantetheine. Limited information is available on these enzymes, but the relatively high abundance of Nudt19 and Nudt7 mRNA in the kidney and liver, respectively, suggests that they play specific roles in the regulation of CoA levels in these organs. Here, we analyzed Nudt19-/- mice and found that deletion of Nudt19 elevates kidney CoA levels in mice fed ad libitum, indicating that Nudt19 contributes to the regulation of CoA in vivo Unlike what was observed for the regulation of Nudt7 in the liver, Nudt19 transcript and protein levels in the kidney did not differ between fed and fasted states. Instead, we identified chenodeoxycholic acid as a specific Nudt19 inhibitor that competed with CoA for Nudt19 binding but did not bind to Nudt7. Exchange of the Nudix and CoA signature motifs between the two isoforms dramatically decreased their kcat Furthermore, substitutions of conserved residues within these motifs identified amino acids playing different roles in CoA binding and hydrolysis in Nudt19 and Nudt7. Our results reveal that the kidney and liver each possesses a distinct peroxisomal CoA diphosphohydrolase.

Transcriptional regulation of dog prostate arginine esterase gene by androgens

These studies were designed to define the molecular events involved in the modulation of dog prostate arginine esterase gene expression following short castration intervals and androgen treatment. Arginine esterase enzymatic activity and protein levels decreased about 50% 24 h after castration. Thereafter, a more progressive decrease was observed, resulting in 2-4-fold lower levels in 12-day castrates than in the intact controls. Total prostatic arginine esterase mRNA levels slowly decreased during the first five days after castration but more abruptly thereafter and were about 150-fold lower in 12-day castrated animals. By contrast, in isolated prostatic nuclei, levels of arginine esterase RNA precursors and mature transcripts rapidly fell following orchiectomy, with a 50-70% decrease 24 h after castration. Nuclear run-on experiments confirmed that the latter effects were the result of decreased arginine esterase gene transcription. All these changes could be at least partially reversed by administration of testosterone cypionate. Furthermore, no striking modifications in the proportion of epithelial/stromal cells in the prostatic tissue were observed following orchiectomy. These results show that castration and androgens exert very rapid effects on the gene expression of arginine esterase, and that the regulation occurs at the transcriptional level.

Effects of androgens on the transcription of secretory protein genes in rat seminal vesicle

Run-on transcription in isolated nuclei has been used to study the effects of testosterone on gene expression in rat seminal vesicles. General transcriptional rates were increased by about 6-fold with an additional 2- to 3-fold differential stimulation of the genes for secretory proteins IV and V. These transcriptional changes are insufficient to explain overall changes in cellular mRNA levels, indicating that androgens must also have major effects on post-transcriptional processing of RNA transcripts or on mRNA stability. Analysis of nuclear RNA by Northern blotting with intron probes suggests substantial androgen effects on primary transcript processing.

Molecular mechanisms of tubulointerstitial hypertrophy and hyperplasia

Adult kidneys, which are principally composed of tubulointerstitium, do not normally regenerate or expand their working pool of functional cells at a very high rate. Loss of kidney tissue, however, can lead to some compensatory renal enlargement. The catalytic forces initiating such exchanges have not been fully articulated by current experimental endeavors. Increasing evidence, nevertheless, does suggest that factors other than simple changes in renal hemodynamics may be involved in this process. Different cellular elements in the tubulointerstitial microenvironment probably modulate changes in tubular enlargement or size through a complex cytokine network. Autocrine and paracrine stimulation of enlargement by different local growth factors also seem to play a pivotal role. After binding to cellular receptors, these factors activate signal transduction pathways resulting in expression of immediate early genes, which by themselves can synchronize the expression of subsequent genes through the medium of transacting factors. The renal enlargement response can also be modified by endocrine hormones that can activate such genes directly and/or stimulate other adjunctive processes, like receptor expression for the regional binding of growth factors. Furthermore, renal enlargement is under negative feedback of inhibitory factors like TGF beta. It is possible, for example, that special genes exist which are only expressed to arrest enlargement. It has been further suggested that activation of the Na+/H+ antiporter is a common denominator in renal enlargement. Recent findings, however, indicate that the activation of this antiporter is not always necessary, and might rather be a parallel event rather than a key phenomena in tubular enlargement. G0/G1 transition of tubular cells seems to involve similar factors in tubular hypertrophy and hyperplasia. The factors which are responsible for the final determination of the enlargement pattern (hypertrophy vs. proliferation) are unknown. The separation between hypertrophy and hyperplasia, although suggested by striking differences in cellular regulation, may be somewhat artificial, since responses leading to tubular enlargement also exist in circumstances where hyperplasia and hypertrophy are combined events. Recently it has been proposed that growth factors stimulate gluconeogenesis in proximal tubular cells producing hyperplasia, whereas factors inhibiting gluconeogenesis might induce hypertrophy. Whether the common pathway message of this intriguing hypothesis is correct still requires further validation.(ABSTRACT TRUNCATED AT 400 WORDS)

Progressive induction of mRNA synthesis for androgen-responsive genes in mouse kidney

A number of mRNAs present in kidney are selectively induced by the administration of androgen to mice. Using a pulse-labelling method to measure in vivo rates of mRNA synthesis, seven androgen-responsive mRNAs were tested. The time courses of induction following testosterone treatment indicated that androgen-responsive mRNA synthesis increases progressively. Depending on the mRNA examined, it took 2-10 days after the start of hormone administration for synthesis rates to reach a maximum. Even the fastest of these inductions is slow compared to response times in other steroid-responsive systems, and is very slow compared to the time required for androgen-receptor complex to accumulate in the nucleus. We conclude that gene activation in response to androgen is a prolonged and incremental process rather than a single event. Two alternative models are proposed: (1) these genes are actually responding to intermediate transcription factors that accumulate progressively in response to androgen; (2) the androgen-responsive genes contain multiple binding sites that have a cumulative effect on transcription as the number of receptor complexes bound increases.