Stimulation by cyclic 3',5'-adenosine monophosphate of RNA synthesis in a mammalian cell-free system

Enhancement by GTP of cAMP binding to hepatic nuclei and cytosol

In the present study we have demonstrated specific binding of 3H-labeled adenosine 3',5'-cyclic monophosphate (cAMP) to a nuclear extract from rat liver. GTP, GDP, and low concentrations of ATP and ADP increased nuclear binding of [3H]cAMP, and AMP inhibited [3H]cAMP binding. Photoaffinity labeling studies employing [32P]cAMP revealed four nuclear binding proteins [relative molecular weight (Mr) 36,000, 49,000, 54,000 and 57,000]. Unlabeled cAMP decreased [32P]cAMP binding to all four proteins, whereas GTP increased binding to the 57,000 protein. We also observed specific binding of [3H]cAMP in the liver cytosol, which was stimulated by GTP but not by ADP or ATP. Photoaffinity labeling studies of the cytosol in the absence of unlabeled nucleotides revealed three cAMP-binding proteins (Mr 36,000, 49,000, and 54,000). Unlabeled cAMP inhibited binding of [32P]cAMP to all three proteins, whereas in the presence of GTP there was binding of [32P]cAMP to a Mr 57,000 protein. Using DEAE-cellulose, we isolated from the nuclear extract and cytosol a cAMP-binding protein that responded to GTP with an increase in cAMP binding but was unaffected by GDP, ATP, ADP, and AMP. Guanosine imidodiphosphate did not affect cAMP binding, suggesting that the stimulatory effect of GTP may be mediated by phosphorylation. We speculate that alterations in intracellular GTP in vivo may modulate the binding of cAMP to a protein in the nucleus and cytosol.

Specific nuclear binding of adenosine 3',5'-monophosphate-binding protein complex with subsequent poly(A) RNA synthesis in embryonic chick cartilage

We used embryonic chick pelvic cartilage as a model to study the mechanism by which cyclic AMP increases RNA synthesis. Isolated nuclei were incubated with [32P]-8-azidoadenosine 3,5'-monophosphate ([32P]N3cAMP) with no resultant specific nuclear binding. However, in the presence of cytosol proteins, nuclear binding of [32P]N3cAMP was demonstrable that was specific, time dependent, and dependent on a heat-labile cytosol factor. The possible biological significance of the nuclear binding of the cyclic AMP-protein complex was identified by incubating isolating nuclei with either cyclic AMP or cytosol cyclic AMP-binding proteins prepared by batch elution DEAE cellulose chromatography (DEAE peak cytosol protein), or both, in the presence of cold nucleotides and [3H]uridine 5'-triphosphate. Poly(A) RNA production occurred only in nuclei incubated with cyclic AMP and the DEAE peak cytosol protein preparation. Actinomycin D inhibited the incorporation of [3H]uridine 5'-monophosphate into poly(A) RNA. The newly synthesized poly(A) RNA had a sedimentation constant of 23S. Characterization of the cytosol cyclic AMP binding proteins using [32P]N3-cAMP with photoaffinity labeling three major cAMP-binding complexes (41,000, 51,000, and 55,000 daltons). The 51,000 and 55,000 dalton cyclic AMP binding proteins were further purified by DNA-cellulose chromatography. In the presence of cyclic AMP they stimulated poly(A) RNA synthesis in isolated nuclei. The 51,000-dalton cyclic AMP-binding protein was the predominant one that bound to the nuclei. While cyclic AMP-dependent protein kinsae activity was present in the cytosol and DEAE peak cytosol proteins, it was not present in the DNA-cellulose-bound, cyclic AMP-binding proteins. We conclude that one possible mechanism by which cyclic AMP increases RNA synthesis is by complexing to a 51,000-dalton cytosol cyclic AMP-binding protein and being subsequently translocated to the nucleus, where it is specifically bound and associated with induction of poly(A) RNA synthesis.

The effects of glucose and cyclic GMP on RNA synthesis and nuclear morphology in starved rats

Feeding rats in diet high in glucose has been demonstrated to inhibit the induction of many enzymes, block the action of glucocorticoids, and, in general, appears to result in decreased cyclic AMP activity. We found that glucose feeding depresses both messenger RNA (mRNA) and non-mRNA synthesis. Electron microscopic examination of the nucleus revealed that glucose feeding decreases the granular component of liver cell nucleoli. It only slightly decreases liver cyclic AMP levels, but produces a sixfold elevation in levels of the cyclic AMP antagonist, cyclic GMP. Administration of bromocyclic GMP, like glucose feeding, depresses mRNA synthesis, but does not simulate the effect of the carbohydrate on nuclear morphology. In addition, glucose feeding halves liver inorganic phosphate and triples ATP levels. Phosphorylation of nuclear proteins, however, remains unaltered. Despite the antagonism between glucose feeding and glucocorticoid activity, the former compound did not change the binding of dexamethasone to liver nuclei.

Stimulation by N6,O2'-dibutyrul andenosine 3',5'-cyclic monophosphate of RNA and DNA synthesis and of cell proliferation of rat hepatocytes in primary tissue culture

The effects of DBcAMP in doses from 1.5 x 10(-8) to 1.5 x 10(-3) M on the compartmental apparent surface area (ASA) and (5(-3H)uridine radioactivity concentration (URC), (methyl-3H)thymidine labelling index per 1 hour ([Me-3H]Tdr LI/h) and per cent mitotic index (MI%) and colchicine metaphase index (CMI%) of young rat differentiated hepatocytes in primary tissue culture were investigated by morphometric and radioautographie methods. In these cells DBcAMP was found to elicit: (1) progressive increments in the ASA of nucleoli, karyoplasm and cytoplasm; (2) peak increases in nucleolar URC at 1.5 x 10(-8) and 10(-5) M, but a slight decrease at 1.5 x 10(-3) M; (3) singificant increments in karyoplasmic and total nuclear URC at all doses, except at 1.5 x 10(-6) and 10(-4) M, when such parameters remained at control levels; (4) steady and progressive increases in cytoplasmic and total cell URC values; (5) marked increments in (Me-3H)Tdr LI/h, MI% and CMI% up to the dose of 1.5 x 10(-4) M, but at 1.5 x 10(-3) M these parameters were found to be either much less enhanced or to approach closely to control values. cAMP in doses from 1.5 x 10(-8) to 10(-4) M also markedly incremented the in vitro hepatocyte CMI%, while having a lesser stimulatory effect at 1.5 x 10(-3)M. Finally of the various possible metabolites of DBcAMP administered at 1.5 x 10(-8) M to liver cultures, N6- and O2'-MBcAMP and, again, cAMP significantly increased the CMI%, of cultured hepatocytes, whereas 5'-AMP, adenosine and allantoin had no significant effect and Na-butyrate slightly decreased it. The present observations strengthen the hypothesis that cAMP and its butyrated derivatives, by possibly amplifying the template activity of the liver chromatin, accelerate the flow of differentiated primary young rat hepatocytes into the various stages of the mitotic cell cycle.

Effect of adenosine 3',5'-cyclic monophosphate on the RNA and DNA synthesis and cell proliferation of rat hepatocytes in primary culture: a radioautographic study

The effect of a 24-h treatment with various doses (from 1.5-10-minus 8 to 3.0-10-minus 3 M) of adenosine 3',5'-cyclic monophospahte (cAMP) on morphometric parameters, [5--3H]uridine radioactivity concentration (URC), [methyl--3H]thymidine [Me--3H]-Tr) labelling index per hour (L.I./h) and per cent mitotic index (M.I.%) of young rat differentiated hepatocytes in primary tissue culture were investigated by morphometric and radioautographic methods. In such cells cAMP was found to induce: (1) a reduction of the apparent surface area (ASA) of total nucleoli, karyoplasm and cytoplasm; (2) significant increases in URC of all the subcellular compartments at all the dosages employed (only cAMP at 1.5-10-minus 8 M did not change karyoplasmic and cytoplasmic URC values); (3) marked increments in [Me--3H]Tdr L.I./h and M.I.% from the lowest dose up to 1.5-10-minus 4 M; at higher doses the L.I./h and M.I.% were less stimulated or approached control values. In cultured rat hepatocytes, adenosine-5'-phosphate (5'-AMP) (1.5-10-minus 4 M per 24 h) increased the karyoplasmic and total cell ASA, the lone total nucleolar URC and both the L.I./h and M.I.%. However, these metabolic effects were significantly less intense than those elicited by isomolar cAMP. Theophylline (Theo) (5.5-10-minus 5 M per 24 h) reduced the in vitro rat hepatocyte total nucleolar ASA but affected neither other morphometric nor any of the URC values. The same dose of Theo plus cAMP (1.5-10-minus M) had no morphometric effect but significantly increased the URC values of all primary rat hepatocyte compartments. Actinomycin D (DAct) (0.1 mug/ml per 24 h) plus cAMP (1.5-10-minus 4 M) decreased the cultured rat hepatocyte total nucleolar ASA but enlarged that of karyoplasm and cytoplasm and, further, markedly curtailed all the compartmental URC values. These data support the hypothesis that cAMP amplified the template activity of the liver chromatin and accelerates the flow of differentiated primary young rat hepatocytes into the various stages of the mitotic cell cycle.

Solubilized DNA-dependent nuclear RNA polymerases from the mammary glands of late-pregnant rats

Mammary gland nuclear extracts from late-pregnant Wistar or Sprague-Dwaley rats, analyzed by DEAE-Sephadex chromatography, were found to contain DNA-dependent RNA polymerases, cyclic nucleotide-binding proteins, and cyclic AMP-independent protein kinases. 1. The fractions from chromatographed nuclear extracts which contained nucleolar enzymes or nucleoplasmic enzyme II, bound radioactive cyclic AMP and cyclic GMP. Other fractions also bound cyclic nucleotides, some preferentially associating with one or the other compound. 2. Cyclic AMP increased the amount of RNA formed by several alpha-amanitin-insensitive fractions containing nucleolar enzymes. 3. Cyclic AMP reduced the amount of RNA formed by column fractions which included nucleoplasmic enzyme II. 4. Cyclic GMP increased the amount of RNA synthesized by column fractions containing enzyme II. 5. Two major cyclic AMP-independent protein kinases which did not elute with enzymes Ib and II, and several minor protein kinases were present. These findings may have important implications for understanding the proximate control of transcription. A relationship between them is not established, but is under study.