Isoproterenol-induced selective phosphorylation in vivo of the 214,000 dalton subunit of rat C6 glioma cell RNA polymerase II

Norepinephrine activates β1 -adrenergic receptors at the inner nuclear membrane in astrocytes

Norepinephrine exerts powerful influences on the metabolic, neuroprotective and immunoregulatory functions of astrocytes. Until recently, all effects of norepinephrine were believed to be mediated by receptors localized exclusively to the plasma membrane. However, recent studies in cardiomyocytes have identified adrenergic receptors localized to intracellular membranes, including Golgi and inner nuclear membranes, and have shown that norepinephrine can access these receptors via transporter-mediated uptake. We recently identified a high-capacity norepinephrine transporter, organic cation transporter 3 (OCT3), densely localized to outer nuclear membranes in astrocytes, suggesting that adrenergic signaling may also occur at the inner nuclear membrane in these cells. Here, we used immunofluorescence and western blot to show that β1 -adrenergic receptors are localized to astrocyte inner nuclear membranes; that key adrenergic signaling partners are present in astrocyte nuclei; and that OCT3 and other catecholamine transporters are localized to astrocyte plasma and nuclear membranes. To test the functionality of nuclear membrane β1 -adrenergic receptors, we monitored real-time protein kinase A (PKA) activity in astrocyte nuclei using a fluorescent biosensor. Treatment of astrocytes with norepinephrine induced rapid increases in PKA activity in the nuclear compartment. Pretreatment of astrocytes with inhibitors of catecholamine uptake blocked rapid norepinephrine-induced increases in nuclear PKA activity. These studies, the first to document functional adrenergic receptors at the nuclear membrane in any central nervous system cell, reveal a novel mechanism by which norepinephrine may directly influence nuclear processes. This mechanism may contribute to previously described neuroprotective, metabolic and immunoregulatory actions of norepinephrine.

Regulation of mouse preimplantation development: inhibition of synthesis of proteins in the two-cell embryo that require transcription by inhibitors of cAMP-dependent protein kinase

Perturbing the changes in protein phosphorylation accompanying the first cleavage can inhibit the appearance of a set of proteins whose synthesis is inhibited by alpha-amanitin (transcription-requiring proteins, TRPs) (W. T. Poueymirou and R. M. Schultz, 1987, Dev. Biol. 121, 489-498); synthesis of the TRPs is likely to represent activation of transcription of the embryonic genome that occurs at the 2-cell stage during mouse development. In the present study, we report the effects of three different inhibitors of the cAMP-dependent protein kinase, N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide (H8), (Rp)-cAMPs, and protein kinase inhibitor (PKI), each of which inhibits the kinase by a different mechanism, on cleavage of 2-cell embryos and synthesis of the TRPs. Two-cell embryos possess PK-A activity, which is inhibited by each of these inhibitors. Both H8 and (Rp)-cAMPs inhibit cleavage of 2-cell embryos in a concentration-dependent manner; similar concentrations of H7, which is a less potent inhibitor of PK-A, do not inhibit cleavage. H8 and (Rp)-cAMPS inhibit in a concentration-dependent manner TRP synthesis, whereas higher concentrations of H7 are required to inhibit TRP synthesis. Microinjected PKI also inhibits synthesis of the TRPs. In addition, H8 inhibits the accumulation of translatable messenger RNAs that are likely to encode for the TRPs. Last, H8, but not H7, inhibits the phosphorylation of a phosphoprotein in 2-cell embryos. Results of these studies suggest a role for protein phosphorylation catalyzed by cAMP-dependent protein kinase in regulating transcription in the early mouse embryo.

Activity of DNA and RNA polymerases in resurfacing rabbit corneal epithelium

Activity of RNA polymerases I, II and III (distinguished using alpha-amanitin) and activity of DNA polymerases alpha and beta (distinguished using N-ethylmaleimide) were assayed for varying intervals and at varying substrate (UTP or dTTP) concentrations in the purified nuclear fraction from corneal epithelium of carbamylcholine-treated and control eyes of rabbits with resurfacing acid burn defects. Incorporation was linear with time for all enzymes up to 30 min. In 10 min assays at varying substrate concentrations, all polymerases from carbamylcholine-treated eyes had significantly elevated Vmax compared to corresponding control enzymes. The drug also increased apparent affinity of RNA polymerase II for UTP and apparent affinity of DNA polymerases alpha and beta for dTTP. Results are discussed in relation to potential mechanisms by which effects of carbamylcholine on polymerase activity may be mediated.

The synergistic interaction of hydrocortisone and dibutyryl cyclic AMP during enzyme induction in hybrids between rat C6 glioma cells and FU5AH hepatoma cells

The hormone-responsive enzymes tyrosine aminotransferase and glycerol-3-phosphate dehydrogenase were studied with respect to current models of the mechanism of glucocorticoid/cAMP interaction during the induction of enzyme activity in responsive cell hybrids between rat C6 glioma cells and rat FU5AH hepatoma cells. The results of experiments involving protein and mRNA synthesis inhibitors, sequential addition of inducers, and the assay of cyclic-AMP-dependent protein kinase could not be adequately explained by any one model of inducer interaction. Comparison of the hybrid clones revealed the presence of factors that may modify induction but that are not essential for synergistic induction.

Cyclic nucleotides in muscarinic regulation of DNA and RNA polymerase activity in cultured corneal epithelial cells of the rabbit

DNA and RNA polymerase activities in the purified nuclear fraction from cultured rabbit corneal epithelial cells were assayed over a range of substrate (labeled dTTP or UTP) concentrations using calf thymus DNA as template. Effects of carbamylcholine on polymerase activities were evaluated over a range of drug concentrations including those saturating muscarinic receptors. Carbamylcholine significantly (p less than 0.001) enhanced activity of both polymerases, both in nuclei incubated with the drug during assay and in nuclei from carbamylcholine-treated cells. Drug effects were blocked by atropine. Regression analysis of Hill plots for variation of polymerase activity with carbamylcholine concentration indicated half-maximal activity of both polymerases at approximately 1 microM carbamylcholine. Mechanisms by which carbamylcholine may alter polymerase activities are discussed in relation to effects of the drug on nuclear enzymes of cyclic nucleotide metabolism and on cyclic nucleotide-dependent protein phosphorylation.

Eukaryotic RNA polymerases

This review will attempt to cover the present information on the multiple forms of eukaryotic DNA-dependent RNA polymerases, both at the structural and functional level. Nuclear RNA polymerases constitute a group of three large multimeric enzymes, each with a different and complex subunit structure and distinct specificity. The review will include a detailed description of their molecular structure. The current approaches to elucidate subunit function via chemical modification, phosphorylation, enzyme reconstitution, immunological studies, and mutant analysis will be described. In vitro reconstituted systems are available for the accurate transcription of cloned genes coding for rRNA, tRNA, 5 SRNA, and mRNA. These systems will be described with special attention to the cellular factors required for specific transcription. A section on future prospects will address questions concerning the significance of the complex subunit structure of the nuclear enzymes; the organization and regulation of the gene coding for RNA polymerase subunits; the obtention of mutants affected at the level of factors, or RNA polymerases; the mechanism of template recognition by factors and RNA polymerase.

On the phosphorylation of yeast RNA polymerases A and B

In exponentially growing cells, RNA polymerase B is exclusively form BI enzyme with several phosphorylated subunits: B220, B23 and possibly B44.5. In RNA polymerase A an average of fifteen phosphate groups are distributed on the five phosphorylated subunits: A190 (6), A43 (4), A34.5 (2), A23 (1-2) and A19 (1-2). Phosphorylation of enzyme A by a yeast protein kinase in vitro adds less than 1 mol phosphate/mol enzyme but occurs essentially at the physiological sites, as shown by a comparison of the peptide patterns obtained by limited proteolysis of subunits 32P-labelled in vivo and in vitro. No evidence was found in favor of a modulation of RNA polymerase activity in vitro or in vivo via phosphorylation.