Cordycepin and α-amanitin: Inhibitors of transcription as probes of aldosterone action

Abstract

Summary. Evidence has been presented for the existence of distinct ]~NA polymerases (I and II) in the rat kidney similar to those described previously in rat liver and identified as nucleolar (I) and nucleoplasmic (II) in location. In adrenalectomized rats, administration of d-aldosterone (1 ~tg/100 g body wt) increased the ratio of polymerase I:II activity as defined by sensitivity to a-amanitin. The time-course of this shift correlated with the previously reported changes in urinary Na and K concentrations, in that a significant change in the I :II ratio was noted 1 to 2 hr before the usual peak change in urinary electrolyte concentrations. In the isolated urinary bladder of the toad, cordycepin inhibited incorporation of 3H-uridine into epithelial RNA--with a half time of 4.3 min-and impaired the action of aldosterone on transepithelial Na transport. These findings as well as earlier studies in the literature imply that aldosterone augments ribosomal RNA synthesis, and that ribosomal or messenger RNA synthesis or both are required for the expression of mineraloeorticoid activity.Steroidal regulation of active Na transport in anuran and mammalian target tissues is apparently mediated by stimulation of DNA-dependent synthesis of RNA and the subsequent de novo synthesis of proteins [6,7,34]. This inference is based, in part, on the finding that actinomycin D impaired mineralocorticoid action [6,10,34]. In addition, aldosterone enhanced the incorporation of precursors into total or nuclear RNA of the urinary bladder of the toad, in vitro and of the rat kidney, both in vivo and in homogenates [5,10,12,13,22,27].Roeder and Rutter [25,26] have recently separated and characterized two eukaryofic DNA-dependent RNA polymerases with distinct functions.

Rapid Enhancement of Chick Intestinal DNA-Dependent RNA Polymerase II Activity by 1α,25-Dihydroxyvitamin D 3 , In Vivo

“…The effectiveness of the inhibitors actinomycin D (14) and a-amanitin (15) also supports a specific role of mRNA in the induction of calcium-binding protein and calcium transport. Yet, numerous other hormones such as testosterone (32) and aldosterone (33) [6][7][8][9] hr is consistent with the lag time for metabolism of the native vitamin to la,25-(OH)r2 D3 and supports our present finding of a direct effect of the hormonal sterol in 2-3 hr (Fig. 2).…”

Aldosterone control of the density of sodium channels in the toad urinary bladder

“…Similarly, Spooner and Edelman (1975) found that aldosterone stimulation of both I~-and transepithelial electrical conductance depended on the metabolic state. (iv) The differential response to substrate repletion 3 to 4 hr after the addition of aldosterone is insensitive to inhibitors of RNA and protein synthesis added at the time of substrate repletion (Fanestil, Herman, Fimognari & Edelman, 1968;Chu & Edelman, 1972). Taken together these results imply that the increase in PN~ is not a sole consequence of synthesis of new channel proteins.…”

Kinetics of RNA Labeling in Toad Bladder Epithelium: Effects of Aldosterone and Related Steroids

“…The mean values were taken from the data in Figs. [2][3][4][5] in which a 30-min [3H]uridine pulse and 90-to 150-min chase were used. These populations cover a wide range of responses from no increase in SCC after SC 9420 or cortisol to maximum increases elicited by aldosterone.…”

“…A variety of findings support this hypothesis including: the presence of nuclear receptors in target tissues (2), effects of inhibitors of RNA and protein synthesis (3)(4)(5)(6), and effects on specific mitochondrial enzymes (7), RNA polymerase activity (5,8), chromatin template activity (9), and incorporation of precursors into total or nuclear RNA (10)(11)(12)(13). Precise definition of regulation of transcription by aldosterone, however, has not yet been achieved.…”