Cyclic AMP, cyclic AMP-dependent protein kinase, and the regulation of gene expression

Moderate dietary protein and energy restriction modulate cAMP-dependent protein kinase activity in rat liver

Very low protein diets result in a desensitization of hepatic cAMP signaling in rats, which is characterized by a loss of cAMP-dependent protein kinase (PKA) activity and type I regulatory subunit (RI). Here we have tested whether more moderate protein restriction (Trial 1) or energy restriction (Trial 2) also modulates hepatic PKA quantity and activity. In trial 1, weanling rats were allowed free access to diets containing normal protein (15%, AL-NP), moderately restricted protein (12.5%, AL-MP) and low protein (7.5%, AL-LP); in trial 2, rats were allowed free access to diet containing 15% (AL-NP) or 0.5% protein (very low protein, AL-VLP) or were energy restricted by pair-feeding a diet isonitrogenous to AL-NP but at 65% of the energy intake (ER-IN) for 14 d. Body weights were lower (P < 0.05) by d 14 in all restricted groups compared with the AL-NP group. The quantity of cytosolic RI was lower (P < 0.05) in AL-LP and AL-VLP, but not in AL-MP or ER-IN, compared with AL-NP. In contrast, there was no effect of diet on RI in the particulate fraction. RII was not changed by moderate and low protein diets in either the cytosol or particulate fraction. However, type II regulatory subunit (RII) was greater in the cytosol of ER-IN and in the particulate fraction of AL-VLP (P < 0.05) compared with AL-NP. Specific activity of PKA was lower in the cytosol and particulate fraction (P < 0.05) in the AL-VLP and ER-IN groups compared with the AL-NP group. In contrast, specific activity of PKA was maintained in cytosol from AL-LP, but lower in the particulate fraction (P < 0.05) compared with AL-NP. In summary, protein restricted-diets lower RI subunit in the cytosol; however, only in rats fed very low protein diets is this loss of RI associated with lower cytosolic PKA activity. In contrast, energy restriction lowers PKA activity in the cytosol and particulate fractions, independent of signficant reduction in RI or RII subunits. Taken together, these data indicate that moderate protein and energy restrictions have differential effects on activity and quantity of PKA.

Cyclic AMP-receptor protein activity in rat preputial cells

Cells from the rat preputial gland--a type of sebaceous gland--exhibited specific responsiveness of cyclic 3',5'-adenosine monophosphate (AMP) dependent protein kinase to stimulation by agents that elevate intracellular cyclic AMP. Electron microscopy shows that the rat preputial gland resembles the human sebaceous gland, not only in terms of containing a sebocyte-like population of cells in an acinar arrangement at different maturational stages, but also in the morphology of its organelles such as abundant and sometimes atypical mitochondria, many perinuclear lysosomes with crystalline inclusions, lipid droplets of various sizes, and peroxisomes. Other cell types, among them duct and inflammatory cells, were evident in the tissue sections, but constituted a minor component. Responses to stimulation of the adenylate cyclase-protein kinase pathways were determined using preputial cells that had been both freshly dispersed and grown in monolayer culture. Stimulation with isoproterenol (IPR) or forskolin (FS) resulted in both cases in an increase of cyclic AMP binding of the regulatory (R) subunits of cyclic AMP-dependent protein kinase, as determined by photoaffinity labeling of R subunits with an azido analog of cyclic AMP ([32P]-8-azido cyclic AMP). Cells from the epidermis under comparable conditions responded to a lesser degree and with a different distribution of R subunit isoforms. There are, therefore, differences in receptor activity as well as in the transduction pathways between the two types of epithelial cell populations. These results indicate that the preputial gland contains precursor cells that differentiate in culture to retain specific molecular mechanisms of action mediated via cyclic AMP.

Role of site-selective cAMP analogs in the control and reversal of malignancy

Two isoforms of cAMP receptor protein, RI and RII, the regulatory subunits of cAMP-dependent protein kinase, transduce opposite signals, the RI being stimulatory and the RII being inhibitory of cell proliferation. In normal cells RI and RII exist at a specific physiological ratio whereas in cancer cells such physiological balance of these receptor proteins is disrupted. Reversal and suppression of malignancy can be achieved when the physiologic ratio of these intracellular signal transducers of cAMP is restored as shown by the use of site-selective cAMP analogs, antisense oligodeoxynucleotides or gene transfer, suggesting new approaches to cancer control.

Independent cyclic AMP and E1A induction of adenovirus early region 4 expression

A cellular transcription factor, ATF, binds to a repeated element in the adenovirus early region 4 (E4) promoter. ATF also binds to other viral early promoter regions and to the cyclic AMP (cAMP) response elements of cellular genes. In this report, we demonstrate that a single ATF-binding site located immediately upstream of the E4 TATA box, between -62 and -46, mediates induction of E4 transcription by 8-bromoadenosine-3',5-cyclic monophosphate or cholera toxin in the human hepatoma cell line HepG2 and rat pheochromocytoma cell line PC12. Different ATF-binding sites in the E4 control region independently conferred cAMP inducibility on the simian virus 40 early promoter in PC12 cells. Induction of E4 expression by cAMP was also observed in virus-infected HepG2 cells. Other viral early promoter regions that contain ATF-binding sites (E1A and E2A) were also induced by cAMP in infected cells. E4 expression was activated by the E1A 13S mRNA products in HepG2 cells. E1A trans activation appears to be distinct from the cAMP response.

Localization of cellular regulatory proteins using postembedding immunogold labeling

Cyclic AMP-dependent protein kinase (cAPK) mediates the effects of catecholamines and hormones that cause elevation of intracellular cyclic AMP levels. The holoenzyme is a tetramer consisting of catalytic (C) and cyclic AMP-binding regulatory (R) subunits. The type I and type II cAPK isoenzymes are defined by R subunits (RI and RII) of differing molecular weight, primary structure, and cyclic AMP-binding properties. Postembedding immunogold labeling procedures and specific polyclonal and monoclonal antibodies to RI, RII, and C were used to study the subcellular distribution of cAPK subunits in several tissues. In the rat parotid gland, both RI and RII were present in the cytoplasm, nuclei, and secretory granules of the acinar cells, whereas secretory granules of intercalated and striated duct cells were poorly labeled. These results confirmed that the acinar secretory granules are the source of R subunits previously identified in saliva by specific photoaffinity labeling techniques. Zymogen granules of pancreatic acinar cells and secretory granules of seminal vesicle cells were labeled with antibody to RII. Pancreatic and seminal fluids were shown to contain cyclic AMP-binding proteins. The granules of several endocrine cells (pituitary, pancreatic islet, intestinal) also labeled with RII antibody. Double labeling of ovarian granulosa cells showed that both RI and C were present in the nuclei and cytoplasm. The localization of cAPK subunits revealed by postembedding immunogold labeling is consistent with the postulated regulatory functions of these proteins in gene expression, cell proliferation, exocytosis, and various metabolic events The widespread occurrence of cAPK subunits in secretory granules and their release to the extracellular environment suggests that they play an important role in secretory cell function.

Subcellular compartmentalization of cAMP-dependent protein kinase regulatory subunits during palate ontogeny

Mammalian palatal ontogeny involves epithelial-mesenchymal interactions, cell differentiation, and cell movements. These events occur on days 12, 13, and 14 of gestation in the C57BL/6J mouse embryo. During this period intracellular cAMP levels and cAMP-dependent protein kinase (cAMP-dPK) levels in the palate transiently elevate. Cyclic AMP activates cAMP-dPK by binding primarily to two types of regulatory subunits of this enzyme, designated as RI and RII. To assess whether differential compartmentalization of the regulatory subunits occurs during palatal ontogeny, cytosolic, nuclear, and particulate fractions were prepared from day 12, 13, and 14 embryonic maxillary and palatal tissue. After photo-affinity labeling of each fraction with 8-azido [32P] cAMP, SDS-PAGE, and autoradiography, autoradiograms were analyzed densitometrically. The RI isoform predominated in the nuclear and particulate fractions on all three developmental days; whereas RII predominated in the cytosolic fractions. Thus, differential compartmentalization of cAMP-dPK may be a means by which cAMP dependent responses are regulated during palatogenesis.

Codominant expression of a mutation affecting the cAMP-dependent protein kinase catalytic subunit in somatic cell hybrids of LLC-PK1 cells

The LLC-PK1 mutant cell lines FIB4 and FIB6 are affected in the catalytic (C) subunit of cAMP-dependent protein kinase (cAMP-PK) such that they possess less than 10% parental activity. However, by Western blot analysis they were shown to possess normal levels of C subunit protein. Somatic cell hybrids were derived between mutant and LLC-PK1 cells, and examined for complementation of the cAMP-PK lesion. Codominant expression of mutant and normal alleles was observed, in that somatic cell hybrids between FIB4 and LLC-PK1, and between FIB6 and LLC-PK1 cells, exhibited cAMP-PK activity 60-75% that of LLC-PK1 cells, intermediate between mutant and normal parental cell lines. The cAMP-PK of the FIB6 x LLC-PK1 and FIB4 x LLC-PK1 hybrids was examined by ion exchange chromatography. In contrast to the FIB6 and FIB4 mutants which lack an active Type I cAMP-PK, the hybrids retained levels of active Type I cAMP-PK greater than 30% that of LLC-PK1, concomitant with the retention of catalytic activity. It was concluded that the loss of Type I kinase in the FIB6 and FIB4 mutants is most likely a consequence of the lesion in the cAMP-PK C subunit. All somatic cell hybrids examined showed levels of cAMP-PK C subunit (as determined by Western blot analysis), and in vivo regulation of cAMP-PK activation (in response to hormonal or nonreceptor-mediated stimulation of adenylate cyclase), completely comparable to those of the parental LLC-PK1 cells. Hence, no aberrant regulation of either cAMP-PK subunit levels or cAMP-PK activities was evident in the somatic cells hybrids. All data were consistent with the hypothesis that FIB4 and FIB6 contain a structural mutation affecting the cAMP-PK catalytic subunit that is expressed phenotypically in the presence of the normal allele.

Site-selective cAMP analogs induce nuclear translocation of the RII cAMP receptor protein in Ha-MuSV-transformed NIH/3T3 cells

Site-selective cAMP analogs, depending on the position of their substituents on the adenine ring, selectively bind to either site 1 or site 2 of the known cAMP binding sites of protein kinase. Treatment of Harvey murine sarcoma virus-transformed NIH/3T3 cells with such site-selective analogs results in growth inhibition and phenotypic reversion, and the combination of a C-8 thio or halogen analog (site 1 selective) with an N6 analog (site 2 selective) produces a synergistic effect. We report here that the growth inhibitory effect of the analogs correlates with the nuclear translocation of the RII cAMP receptor protein, the regulatory subunit of protein kinase type II. The transformed NIH/3T3 cells contained no detectable level of RII in the nucleus, whereas nontransformed NIH/3T3 cells exhibited a high level of nuclear RII. Within 30 min after treatment of the transformed cells with the site-selective analogs, immunofluorescence against the RII protein markedly increased in the cell nucleus. The nuclear translocation of the RII cAMP receptor protein is an early event in the reverse transformation of the fibroblasts treated with site-selective cAMP analogs.

Multiple mRNA species code for the catalytic subunit of the cAMP-dependent protein kinase from LLC-PK1 cells. Evidence for two forms of the catalytic subunit

We present evidence for the existence of two forms of the catalytic (C) subunit of the cAMP-dependent protein kinase. A lambda gt-11 cDNA library constructed from poly(A)-rich RNA from the porcine kidney cell line, LLC-PK1, was screened using a 1.5-kb EcoRI fragment from a bovine cDNA for the C subunit. Two independent classes of cDNAs were identified on the basis of partial restriction map and sequence data. These two cDNAs, lambda CAT4 and lambda CAT3, apparently encode two forms of C subunit designated C alpha and C beta, respectively. The nucleotide sequence of the C alpha and C beta cDNAs revealed differences in the coding region and particularly in the 3' untranslated region. However, the deducted amino acid sequences of C alpha and C beta subunits were 96% homologous to the sequences so far determined. Specific probes from the 3' coding region of the two cDNA species were used to investigate C subunit mRNA expression in LLC-PK1 cells. Northern analysis showed a major mRNA species of 2.8 kb with the C alpha probe while the C beta probe detected two mRNA species of 5.0 kb and 3.8 kb. These data were supported by genomic blot analysis which showed distinct hybridization patterns with either the C alpha or C beta probes. All the available evidence suggests that at least two distinct genes encode the C subunit which are expressed in LLC-PK1 cells.

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 effect of cyclic AMP on the accumulation of newly synthesized protein in the extracellular matrix of PFHR-9 teratocarcinoma cells

The effect of elevated cyclic AMP levels on the accumulation of newly synthesized extracellular matrix protein was examined in PFHR-9 cells producing Type IV collagen. The effect of dbcAMP, 8-BrcAMP, IBMX and forskolin on the synthesis of total protein, non-collagen protein and collagen were compared. DbcAMP increased the accumulation of total protein but did not affect the distribution of collagen and non-collagen protein. 8-BrcAMP, IBMX and forskolin also increased collagen and non-collagen accumulation. However, the effect on collagen was significantly greater with 8-BrcAMP and IBMX. Consequently, 8-BrcAMP and IBMX resulted in an increased percent collagen synthesis in the extracellular matrix. Elevated cAMP levels had no effect on cell proliferation or DNA synthesis but did produce a significant effect on cell morphology.

Effect of inhibition of the catalytic activity of cyclic AMP-dependent protein kinase on mitosis in PtK1 cells

Evidence has suggested that cyclic AMP, acting through activation of the type II cyclic AMP-dependent protein kinase, may play a role in the regulation of interphase and mitotic microtubules. In order to examine the potential role of the type II cAMP-dependent kinase during mitosis, dividing PtK1 cells were microinjected with two specific inhibitors of the catalytic activity of the type II kinase. These inhibitors were a specific protein inhibitor of cAMP-dependent protein kinase (PKI) and an affinity-purified polyclonal antiserum (anti-C) directed against the catalytic subunit of the kinase. Both have been shown previously to inhibit kinase activity in vitro. Microinjection of PKI during early- to mid-prophase significantly delayed the progression of the cells through mitosis, with the greatest delay occurring in metaphase. PKI injected during prometaphase also delayed progression through mitosis but to a lesser extent. Microinjection of anti-C during early- to mid-prophase also caused a significant delay in the completion of mitosis, with many cells becoming "hung up" in prometaphase. Anti-C injected during prometaphase had little effect on subsequent progression through mitosis. Microinjection of either anti-C or PKI during metaphase had no discernible effect. No effect on anaphase movement of chromosomes was observed with any treatment. These results provide further evidence that cAMP-dependent phosphorylation may be involved in the regulation of mitosis, although whether it acts directly through regulation of mitotic spindle microtubules is unclear.

Localization of nuclear subunits of cyclic AMP-dependent protein kinase by the immunocolloidal gold method

An immunocolloidal gold electron microscopy method is described allowing the ultrastructural localization and quantitation of the regulatory subunits RI and RII and the catalytic subunit C of cAMP-dependent protein kinase. Using a postembedding indirect immunogold labeling procedure that employs specific antisera, the catalytic and regulatory subunits were localized in electron-dense regions of the nucleus and in cytoplasmic areas with a minimum of nonspecific staining. Antigenic domains were localized in regions of the heterochromatin, nucleolus, interchromatin granules, and in the endoplasmic reticulum of different cell types, such as rat hepatocytes, ovarian granulosa cells, and spermatogonia, as well as cultured H4IIE hepatoma cells. Morphometric quantitation of the relative staining density of nuclear antigens indicated a marked modulation of the number of subunits per unit area under various physiologic conditions. For instance, following partial hepatectomy in rats, the staining density of the nuclear RI and C subunits was markedly increased 16 h after surgery. Glucagon treatment of rats increased the staining density of only the nuclear catalytic subunit. Dibutyryl cAMP treatment of H4IIE hepatoma cells led to a marked increase in the nuclear staining density of all three subunits of cAMP-dependent protein kinase. These studies demonstrate that specific antisera against cAMP-dependent protein kinase subunits may be used in combination with immunogold electron microscopy to identify the ultrastructural location of the subunits and to provide a semi-quantitative estimate of their relative cellular density.

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.

The phosphoform of the regulatory subunit RII of cyclic AMP-dependent protein kinase possesses intrinsic topoisomerase activity

The phosphoform of the type II regulatory subunit (phospho-RII-cAMP) of cAMP-dependent protein kinase from rat liver was found to possess intrinsic topoisomerase activity towards several DNA substrates such as phi X174, pBR322, SV40, and M13. Like the type I topoisomerases from several eukaryotic cells, phospho-RII X cAMP can relax both positive and negative superhelical turns of phi X174 DNA. Topological isomers with a decreasing number of superhelical turns can be identified as transient products. Conditions under which phospho-RII X cAMP relaxes superhelical phi X174 DNA lead to transient formation of a DNA-phospho-RII X cAMP complex via DNA strand breakage and covalent attachment of the DNA to a tyrosine residue of phospho-RII X cAMP via a phospho-RII X cAMP depends on the presence of cAMP and is altered by changes in the degree of phosphorylation of RII. Both dephosphorylation and removal of cAMP from phospho-RII X cAMP abolish its topoisomerase activity.

Cyclic-AMP-dependent protein kinase type II is associated with the Golgi complex and with centrosomes

The subcellular distribution of the type II enzyme of cAMP-dependent protein kinase (cAMP-dPK II) in epithelial and fibroblastic cells was determined by indirect immunofluorescence microscopy. In interphase cells both regulatory (R II) and catalytic (C) subunits were concentrated in a perinuclear area. By comparison of the R II distribution with the location of a bona fide Golgi membrane constituent, this area was identified as the Golgi complex. The cytochemical localization of R II was confirmed by subcellular fractionation. In addition, cAMP-dPK II was associated with microtubule-organizing centers, in particular with mitotic spindle poles. These distributions of cAMP-dPK II probably represent important factors in mediating the effects of cAMP on basic cellular activities ranging from secretion and proliferation to cell shape and motility.

Cell-cycle-specific activity of cyclic nucleotide phosphodiesterase in Physarum polycephalum

The cell-cycle-related activities of the cAMP- and cGMP-dependent phosphodiesterases of Physarum polycephalum were assayed. The activities of plasmodial homogenate and of selected subcellular fractions were measured. The results suggested the presence of both cAMP- and cGMP-dependent phosphodiesterase in the isolated nuclei of P. polycephalum. In addition, they reveal that the cAMP- and cGMP-dependent phosphodiesterase activities of the subcellular fractions fluctuate throughout the cell cycle. The whole-cell homogenates exhibit no cell-cycle-related changes in the presence of 5 X 10(-4) M cGMP. Kinetic data suggest the presence of multiple phosphodiesterase activities in the homogenate and its particulate fractions for the cGMP-dependent enzyme. Multiple cAMP activities are also suggested for the particulate fractions. The Km values indicate that the substrate affinities of the phosphodiesterases from P. polycephalum are similar to those found previously in mammalian systems.

Microheterogeneity of rat parotid gland proteins after chronic treatment with isoproterenol

Two ultrasensitive methods were employed to determine the effect of repeated in vivo stimulation with isoproterenol on the protein composition of parotid acinar cells. Silver staining showed electrophoretic banding pattern changes in a wide range of cellular proteins during and after multiple injections of the beta-adrenergic agonist. Photo-affinity labeling with [32P]-N3-cyclic AMP showed the disappearance and eventual return (after discontinuation of the injections) of the cellular cyclic AMP-binding proteins as measurable cellular components. These findings indicate that major translation-associated changes may occur in target cell protein composition both during and after hormonal stimulation.

Specificity and inhibition of glucocorticoid-induced macrocortin secretion from rat peritoneal macrophages

The secretion of the phospholipase A2-inhibitor macrocortin and the binding of dexamethasone were studied in suspensions of rat peritoneal macrophages. Corticosteroid-induced macrocortin secretion was specific for glucocorticoids and did not occur in response to glucocorticoid antagonists or other steroids or in response to non-steroid macrophage activators (formyl-methionyl-leucyl-phenylalanine f-MLP), the calcium ionophore A23187, phorbol myristate acetate (PMA) and lipopolysaccharide-E.-coli(LPS) ). The apparent potency of competition by secretory glucocorticoids for dexamethasone binding to the macrophage parallelled their ability to induce secretion, implying that these binding sites represent the receptors by which macrocortin secretion is initiated. Agents which interfere with microtubule assembly (colchicine, vinblastine and trimethylcolchicinic acid) and prostacyclin and dibutyryl cyclic AMP inhibit macrocortin secretion. Inhibition studies of glucocorticoid-induced macrocortin secretion also suggest dependence upon metabolic energy, a source of Ca2+ and proteolysis and glycosylation prior to secretion.

Elution of the regulatory subunit of cAMP-dependent protein kinase Type I isozyme derived from epididymal fat within the type II isozyme chromatographic peak

No cAMP-dependent protein kinase activity is found upon DEAE-cellulose chromatography of mouse fat extracts at the low salt concentration characteristic of the Type I isozyme. The RI detected in fat extracts by photoincorporation of the analog, 8-N3 [32P]cAMP, elutes within the high salt Type II isozyme peak. The multiple charge variants of this photolabeled RI which can be resolved by two-dimensional gel electrophoresis are similar to those of the histoptypically-related cultured cells, SV3T3 and 3T6, which do contain Type I kinase isozyme activity peaks. This high salt-eluting RI may be part of a Type I holoenzyme whose elution properties are altered by interactions with other substances present in the extract.

Polyamine levels and diamine oxidase activity in hypertrophic heart of spontaneously hypertensive rats and of rats treated with isoproterenol

Polyamine levels and diamine oxidase (EC 1.4.3.6) activity were studied in hypertrophic heart of spontaneously hypertensive rats as well as in the heart of Wistar rats during the development and regression of cardiac hypertrophy induced by isoproterenol administration. In spontaneously hypertensive rats, putrescine content and diamine oxidase activity were higher than those found in normotensive Kyoto-Wistar control rats. During the development of cardiac hypertrophy induced by isoproterenol, there was an increase in polyamine content and diamine oxidase activity. The administration of cycloheximide or actinomycin D prevented the increase in diamine oxidase activity during the first 24 h after isoproterenol administration, demonstrating that the rise in diamine oxidase activity was due to synthesis of new enzyme. Following the cessation of isoproterenol treatment, cardiac hypertrophy regressed and polyamine levels and diamine oxidase activity diminished toward control values. The administration of aminoguanidine to isoproterenol-treated rats caused in the heart an inhibition of diamine oxidase activity that led to an increase in putrescine level beyond the values found in animals given isoproterenol alone. The results suggest that the enhancement of diamine oxidase activity plays a role in the regulation of putrescine level in hypertrophic heart.

Association of thyroid hormone receptors with chromatin

A large body of circumstantial evidence indicates that receptors located in nuclei of T3 responsive tissues represent a site of initiation of thyroid hormone action at the cellular level. Partial characterization of T3 receptors indicates that these proteins are monomeric structures in nuclei and are chromatin-associated non-histone proteins. Treatment of rat liver nuclei with either pancreatic DNase I or micrococcal nuclease releases T3 receptors from nuclei in two forms: a predominant (95 400 Mr; 5.5-6.0S) and a minor (265 000-365 000 Mr; 12.5S) nucleoprotein complex. Similar structures are excised from rat kidney, brain, and heart nuclei and from GH1 pituitary cell nuclei by micrococcal nuclease digestion. These endonuclease-excised receptor-containing complexes are significantly larger than the salt-extracted receptor (50 000 Mr; 3.5S). The presence of DNA and other non-receptor proteins in these structures indicates that T3 receptors probably function within multimeric complexes in vivo. Although T3 receptors appear to be associated with DNA between nucleosomes, i.e. linker DNA, it is not entirely clear whether all or only a fraction of T3 receptors interact with nucleosomal components. The 12.5S receptor-containing nucleoprotein complex may represent T3 receptors in association with linker DNA and nucleosomal components. T3 receptors do not appear to be uniformly distributed to all chromatin fractions, but are associated with structures having characteristics of transcriptionally active chromatin. They are found in a region of chromatin which is enriched in RNA polymerase activity, rapidly labeled RNA and non-histone proteins, and depleted of histone Hl. This region is also highly sensitive to both micrococcal nuclease and pancreatic DNase I digestion. The association of receptors with transcriptionally active chromatin, however, must be considered provisional until additional details of the precise receptor-chromatin interaction have been established. The recent demonstration of a 20-fold increase in a specific hepatic mRNA four hours following administration of T3 to hypothyroid rats indicates that thyroid hormone potentially has very rapid effects on hepatic gene expression. However, significant changes in nuclear protein phosphorylation, nuclear protein composition, and chromatin structure have not been detected within this four-hour period. Thus, effects of T3 on hepatic gene expression are brought about by local and presumably subtle changes in nuclear function.

Fractionation and partial purification of rat liver nuclear protein kinases

We have fractional and partially purified several rat liver nuclear protein kinases by utilizing endogenous (nonhistone proteins) and exogenous acidic (dephosphophosvitin) and basic (lysine-rich histone) protein substrates. Three enzymes were active towards endogenous substrates, two towards dephosphophosvitin and two towards lysine-rich histone. Of the latter only one was cAMP-dependent, however, only minimal cAMP binding activity was detected. Several features of these enzyme reactions are described revealing distinct differences in the characteristics of each of these enzymes.

Ornithine decarboxylase may be a multifunctional protein

Ornithine decarboxylase may undergo posttranslational modifications which alter its function. Both transamidation of glutamine residues in the enzyme catalyzed by TGase and phosphorylation of serine and threonine residues catalyzed by a polyamine-stimulated protein kinase have been demonstrated. Data are presented which suggest that these modifications result in translocation of the modified protein to the nucleolus where it regulates the activity of RNA polymerase I to transcribe rDNA, the only active nucleolar genes. Transamidation of specific proteins with primary amines catalyzed by intracellular TGase may be an important posttranslational modification, capable of altering genetic transcription. The rapid half-life of ODC (10-15 min) may be related to rapid posttranslational modification with loss of enzymatic activity rather than to protein degradation.

Inhibition of ornithine decarboxylase activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the activity of rat liver ornithine decarboxylase (ODC) were investigated. Sixteen hours after partial hepatectomy, rats that had been pretreated with TCDD for 1 week exhibited a 3- to 4-fold increase in ODC activity, while vehicle controls exhibited to 8- to 10-fold increase. This inhibition of ODC induction by TCDD was time dependent since TCDD administration at the time of partial hepatectomy did not produce inhibitory effects on the subsequent ODC induction. ODC induction after either aminophylline or dexamethasone administration, agents which act via cAMP-mediated and direct nuclear events, respectively, also was inhibited by pretreatment with TCDD. It was concluded that TCDD pretreatment decreased the ability of the liver to respond to hormonal stimulation as reflected in the attenuation of ODC induction. RNA polymerase I activity, which positively correlates with ODC activity in growth and development, decreased concomitantly with decreased induction of ODC. In unstimulated liver RNA polymerase I activity, as well as protein, DNA, and RNA levels, remained unchanged 1 week after TCDD. However, TCDD administration resulted in decreased liver concentrations of putrescine and spermidine, but not spermine. This suggests that TCDD pretreatment results in a time-dependent decrease in hormone responsivity.

Determination and comparative analysis of the catalytic subunit of adenosine 3',5'-cyclic phosphate-dependent protein kinase by an enzyme-linked immunosorbent assay

A specific antiserum against bovine heart catalytic subunit was used for the determination of the catalytic subunit in an enzyme-linked immunosorbent assay. Under the conditions elaborated the assay has a lower detection limit for catalytic subunit of 0.25 pmol/ml. In crude bovine heart extracts the concentration of catalytic subunit was determined by this method to be 0.18 +/- 0.02 mumol/kg wet wt. The immunochemical comparison of various animal species and cells, including organisms like amoebae and yeast, shows the broad applicability of the assay and provides evidence that the catalytic subunit is a highly conserved molecule.

n-Tetradecanoyl is the NH2-terminal blocking group of the catalytic subunit of cyclic AMP-dependent protein kinase from bovine cardiac muscle

The unusual NH2-terminal blocking group of the catalytic subunit of bovine cardiac muscle cyclic AMP-dependent protein was found to be amide-linked n-tetradecanoic acid by gas chromatographic-, direct chemical ionization-, and fast atom bombardment-mass spectrometry. In addition, fast atom bombardment mass spectrometry revealed the presence of an additional alanine which had been overlooked when the original sequence was determined. The corrected and completed NH2-terminal sequence of the 350-amino acid catalytic subunit is CH3(CH2)12CONH-Gly-Asn-Ala-Ala-Ala-Ala-Lys.

Early events in the response of fast skeletal muscle to chronic low-frequency stimulation. Polyamine biosynthesis and protein phosphorylation

The concentrations of putrescine, spermidine and spermine and the activities of ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (SAM-D) were investigated in fast muscle subjected to chronic low-frequency electrical stimulation. Both ODC and SAM-D activities increased markedly between 18 and 48 h of stimulation. Changes in enzyme activities were followed by phasic elevations in the concentrations of putrescine, spermidine and spermine. Peak levels were reached first by putrescine at 3-4 days, followed by spermidine at about 9 days and then by spermine at about 11 days. A possible relationship was sought between these events and changes produced in vitro in the phosphorylation pattern of cytoplasmic proteins and the total activity of cyclic AMP-dependent protein kinase. However, during the early stages of stimulation, no prominent changes were seen either in the phosphorylation pattern or in the activity of cyclic AMP-dependent protein kinase. These characteristics changed significantly at a later stage (by 12 days of stimulation) and became indistinguishable from those of slow muscle by 3 to 4 weeks of stimulation.

Direct cytochemical localization of catalytic subunits dissociated from cAMP-dependent protein kinase in Reuber H-35 hepatoma cells. II. Temporal and spatial kinetics

The activation of cyclic AMP-dependent protein kinase has been found to be the predominant mode by which cyclic AMP (cAMP) leads to alterations of a large variety of cellular functions. The activation of the kinase results in the release of the catalytic subunit which as the free enzyme possesses phosphotransferase activity for a variety of specific protein substrates. Using a sensitive and specific cytofluorometric technique we monitored the appearance of free catalytic subunit in Reuber H35 hepatoma cells in culture after incubation with N6-1'-O-dibutyryl-cyclic AMP (DBcAMP), 8-bromoadenosine-3':5'-cyclic monophosphate (8-BrcAMP), and glucagon. The cytochemical method employs the heat-stable inhibitor of the free catalytic subunit which has been conjugated to fluorescein isothiocyanate (F:PKI) and was validated as described in the companion paper (Fletcher and Byus. 1982. J. Cell Biol. 93:719-726). Here we studied the temporal and spatial kinetics of the free catalytic subunit following activation of cAMP-dependent protein kinase by increasing concentrations of DBcAMP,8-BrcAMP, and glucagon. Under similar conditions protein kinase activation was also assessed biochemically in H35 cell supernatants by assaying the protein kinase activity ratio. Incubation of the hepatoma cells with DBcAMP (0.1 mM) led to an increase in the activity ratio from 0.2 in control cultures to a value of nearly 1.0 within a 1- to 2-h period. During this same period using the F:PKI probe, a significant increase in cytoplasmic and nucleolar fluorescence indicative of the release of the free catalytic subunit was coincidentally observed. In contrast to the rapid appearance of catalytic subunit in the cytoplasm and nucleolus of the cell within 5-15 min of the addition of DBcAMP, discernible nucleoplasmic fluorescence did not occur until after 1 h. H35 cell cultures incubated with 8-BrcAMP (0.01-1.0 mM) exhibited a more rapid activation of the protein kinase measured cytochemically compared to the cells treated with DBcAMP. Cultures incubated with 8-BrcAMP had significantly increased cytoplasmic and nucleolar fluorescence compared to unstimulated cells within 1 min of the addition of the analogue and reached a maximal level within 15 min. By employing a microspectrophotometer a distinct dose-dependent increase in cellular fluorescence (i.e., free catalytic subunit) was observed as the concentration of 8-BrcAMP was increased from 0.01 to 1.0 mM at 1, 5, 15, and 60 min following stimulation. The addition of glucagon (10(-6) M) to the culture also led to the activation of cAMP-dependent protein kinase as determined by an increase in the activity ratio. This increase was paralleled throughout the incubation period by a marked elevation in cytoplasmic and nucleolar fluorescence. The results reported herein suggest that both cyclic nucleotide analogues and a polypeptide hormone lead to the activation of cAMP-dependent protein kinase in similar intracellular compartments in Reuber H35 hepatoma cells...

Influence of 3-methylcholanthrene on liver nucleolar and nucleoplasmic activities of protein kinases and RNA polymerases

The experiments were designed to investigate some details of the action of 3-methylcholanthrene (3-MC) on the regulation of transcription. After a single intraperitoneal dose of 3-MC a significant increase in the activities of both nucleolar and nucleoplasmic protein kinases in hepatic cells of young rats was found. The maximal stimulation took place 24 hr after the administration of 3-MC and the extent of activation was much greater in the nucleolar fraction. There is a significant elevation of the activities of both functional forms, free and template-engaged, of RNA polymerase A 24 hr after a single injection of 3-MC. Free and engaged forms of extranucleolar RNA polymerase B show a different behaviour: after 24 hr of 3-MC administration the engaged form is markedly enhanced while the activity of the free enzyme shows a significant decrease. The more moderate increase in total RNA polymerase B activity is obviously preceded by a transfer of the enzyme from 'free' to 'engaged' form. Since the enhancement of protein kinase activities was accompanied by the stimulation of nuclear RNA polymerases we suggest that both kinds of enzymes are involved in an epigenetic mechanism of the inducing action of 3-MC on cytochrome P1-450.

Cyclic AMP-dependent protein kinase content of murine splenic T and B lymphocytes and non-lymphoid tissues

Cyclic AMP-dependent protein kinase activity has been measured in DEAE-cellulose elution profiles of highly enriched murine splenic T and B Lymphocytes. B Lymphocytes were found to contain about 10% of the amount of enzyme activity associated with T lymphocytes and several non-lymphoid tissues. Cyclic AMP-independent casein kinase activities were equivalent in T and B lymphocytes. Lymphocytes contained predominantly type I isozyme as opposed to several non-lymphoid tissues which all contained predominantly the type II form.

The role of cyclic AMP in the induction of estrogen and progestin synthesis in cultured granulosa cells

The role of cyclic AMP in the induction of enzymes involved in estrogen and progestin biosynthesis in undifferentiated granulosa cells was investigated. When granulosa cells from immature hypophysectomized, DES-treated rats were cultured for 2 days in serum-free medium with aromatase substrate (10(-7) M androstenedione) together with graded doses of FSH, prostaglandin E2 (PGE2), cholera toxin (CT), or dibutyryl cyclic AMP (Bu2cAmP), there was a dose-related increase in estrogen (E) production. The induction of E production by saturating doses of FSH, PGE2, CT, and Bu2cAmP required a lag phase of approximately 24 h, after which the E response increased sharply to maximum levels at day 3, and then declined gradually to day 5. Treatment for 24 h ((day 0-1) with FSH, together with 1 microgram/ml of either actinomycin D or cycloheximide, completely abolished the stimulatory action of FSH on E production. When the inhibitors were removed, the FSH-induced increases in E returned to near normal levels after a 24-h lag period. Similar effects of the inhibitors upon E production by CT, PGE2 and Bu2cAMP were observed. As with E, the production of progesterone and 20 alpha-dihydroprogesterone was markedly stimulated by FSH, PGE2, CT and Bu2cAmP, and the results of the time course, dose response, and inhibitor experiments were similar to those for E production. These results indicate that FSH induces the de novo synthesis of enzymes required for both estrogen and progestin biosynthesis by undifferentiated granulosa cells and suggest that this action is mediated by cyclic AMP.

Neurotransmitter modulation of steroid action in target cells that mediate reproduction and reproductive behavior

Two major functional interactions between steroid hormones and neurotransmitters are generally recognized. First, steroids affect neurotransmission, and second, through effects on hypothalamic peptides that regulate anterior pituitary function neurotransmitters affect steroid secretion. In recent years, evidence has accumulated which indicates that neurotransmitters can also affect steroid action within postsynaptic steroid target cells. We review evidence for this relationship in pineal, uterus and hypothalamus and propose that the modulation of target cell responsiveness to steroids is an important mechanism by which neurotransmitters affect steroid-dependent processes. The operation of such a mechanism provides a means for environmental, behavioral and emotional events to rapidly and selectively alter steroid effects on behavior and physiology.

Specificity of muscarinic acetylcholine receptor regulation by receptor activity

Regulation of muscarinic acetylcholine receptor concentration by receptor activity in neuron-like NG108-15 hybrid cells is a highly specific process. Receptor levels, monitored by binding of [3H]quinuclidinyl benzilate ([3H]QNB), decreased 50--75% following 24-h incubation of cells with muscarinic agonists, but none of the following cellular processes was altered by this chronic receptor stimulation: (1) glycolytic energy metabolism, measured by [3H]deoxy-D-glucose ([3H]DG) uptake and retention; (2) rate of cell division; (3) transport, measured by [3H]valine and [3H]uridine uptake; (4) RNA biosynthesis, measured by [3H]uridine incorporation; (5) protein biosynthesis, measured by [3H]valine and [35S]methionine incorporation into total protein and into protein fractions obtained by polyacrylamide gel electrophoresis. In contrast, chronic stimulation did cause a threefold decrease in the capacity of carbachol to stimulate phosphatidylinositol (PI) turnover, a receptor-mediated response. In addition to cholinomimetics, the neuroeffector adenosine (1 mM for 24 h) also caused a decrease in [3H]QNB binding levels, but chronic stimulation of alpha-adrenergic, opiate, prostaglandin E1, and prostaglandin F2 alpha receptors found on NG108-15 cells caused no changes. The data indicate that loss of muscarinic receptors caused by receptor stimulation is not a consequence of fundamental changes evoked in overall cellular physiology but reflects a specific regulation of cholinoceptive cell responsiveness.

Behavioral effects of temperature sensitive mutations affecting metabolism of cAMP in Drosophila melanogaster

Temperature-sensitive mutations affecting metabolism of cAMP were obtained in Drosophila melanogaster to elucidate the possible involvement of cAMP in behavior. Temperature-dependent hypersensitivity to theophylline, propranolol and dihydroergotoxin following treatment with ethylmethanesulfonate was used to screen for such mutations in the X-chromosome. Biochemical analysis of cAMP content and activity of phosphodiesterase revealed two mutants with increased content of cAMP, 2 mutants with low activity of phosphodiesterase and 1 mutant with high activity of the enzyme. Locomotor activity of the ts-mutants correlated with cAMP content, increasing at 29 degrees C in mutants with an enlarged amount of cAMP and in mutants with low activity of phosphodiesterase and decreasing in the mutants with high activity of the enzyme. The latter mutant also failed to learn to avoid shock-associated odorant. One of the mutants with increased content of cAMP, but insensitive to propranolol, displayed better learning ability than the wild type. The learning performance of the mutants is interpreted proceeding from the metabolism of cyclic nucleotides in cholinergic and dopaminergic structures of the brain.