Phosphorylative modification of histone H1 subspecies following isoproterenol and N6,O2'-dibutyryl cyclic AMP stimulation of rat C6 glioma cells

Selective modulation of protein kinase A and protein kinase C activities in epidermal growth factor (EGF)-stimulated MCF-7 breast cancer cells

In human MCF-7 breast cancer cells, both protein kinase A (PKA) and different members of the protein kinase C (PKC) family are stimulated upon binding of epidermal growth factor (EGF) to cell surface receptors. Selective stimulation of calcium-dependent PKCs with 10(-6) to 10(-9) M Thymeleatoxin significantly increased the proliferation rate of MCF-7 cells over 5 days in culture. This stimulation was blocked by the PKC antagonist Chelerythrine. In contrast, selective activation of PKA by addition of 1 mM dibutyryl cyclic AMP (dBcAMP) did not affect the proliferation rate of MCF-7 cells. Similarly, activation of the adenylate cyclase by 1 microM Forskolin and inhibition of PKA by the cyclic AMP analogue Rp-cAMPS did not modulate the proliferation rate of these cells. Activation of PKC stimulated the expression of the immediate early gene c-fos but c-myc expression was not significantly enhanced. On the other hand, PKA activation increased both c-myc and c-fos expression in MCF-7 cells. These results suggest that PKA activation and c-myc expression are not obligatory for proliferation of MCF-7 cells.

The lysine-rich H1 histones from the slime moulds, Physarum polycephalum and Dictyostelium discoideum lack phosphorylation sites recognised by cyclic AMP-dependent protein kinase in vitro

Calcium chloride-extracted histones were prepared from nuclei of the slime moulds, Physarum polycephalum and Dictyostelium discoideum, and phosphorylation by purified preparations of cyclic AMP-dependent protein kinase (cAMP-d PK) and growth-associated H1 histone kinase (HKG) examined and compared. Among the major histone fractions and other proteins in the two preparations, the H1 histones from both organisms were found to be effective and exclusive substrates for HKG. cAMP-d PK, which phosphorylates mammalian H1 histone and certain, in particular H2B, of the mammalian core histones, phosphorylated several of the core histones from both slime moulds but did not phosphorylate H1 histone from either. The slime mould H1s remained ineffective substrates for cAMP-d PK even after extensive alkaline phosphatase treatment of the histone preparations. Additional studies demonstrated that the lack of slime mould H1 phosphorylation by cAMP-d PK was not due to competition of the H1 molecules with the core histones for the kinase. Our studies suggest that H1 histones from these organisms, whilst clearly containing sites for phosphorylation by HKG, apparently lack phosphorylation sites recognised by cAMP-d PK. Thus, the mediation of specific nuclear functions by cAMP-dependent phosphorylation of H1 in higher organisms may not occur or be required in these lower eukaryotes.

Synthesis of glial fibrillary acidic protein in rat C6 glioma in chemically defined medium: cyclic AMP-dependent transcriptional and translational regulation

Glial fibrillary acidic protein (GFA) expression was induced in rat C6 glioma in chemically defined medium by the addition of N6, O2'-dibutyryl cyclic AMP (dbcAMP). Induction was dependent on the increase in intracellular cyclic AMP (cAMP), which was linearly correlated with added dbcAMP. Contrary to GFA mRNA synthesis, which can be obtained by cAMP-dependent and -independent pathways, translation of mRNA into GFA was observed only above a cellular cAMP concentration of approximately 0.2 fmol/cell. dbcAMP stimulation did not affect the vimentin concentration, which remained at a low level, but changed the cellular morphology from a bipolar to a stellate shape. A similar morphological change was observed after stimulation of C6 with lipopolysaccharide (LPS). However, LPS did not significantly increase the intracellular concentration of cAMP and the LPS-induced mRNA was not translated into GFA. Our results indicate that GFA synthesis is regulated at the mRNA level and at the translational level and that a cAMP-dependent mechanism determines the ultimate synthesis of GFA by a yet unknown mechanism.

Microheterogeneity in H1 histones and its consequences

The extent of microheterogeneity of H1 histones in individual higher organisms, without considering post-translational modifications, is such that five to eight molecular species can be recognized. The H1 variants differ among themselves in their ability to condense DNA and chromatin fragments, and they are non-uniformly distributed in chromatin. This review assembles data that support the notion that the differences in chromatin condensation (heterochromatization) observed through the microscope are maintained by the non-uniform distribution of H1 variants, and that this pattern of chromatin condensation may determine the dynamics of chromatin during replication and may represent the commitment aspect of differentiation. The differential response of the multiple H1 variants with regard to their synthesis and turnover is consistent with this notion.

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.

Regulation of lactate dehydrogenase gene expression by cAMP-dependent protein kinase subunits

The studies described in this report suggest a rather complex, albeit incomplete, sequence of molecular events that we believe form part of the cascade of reactions through which a series of hormones, via cAMP, regulates the expression of specific gene products. The majority of our own studies relate to cAMP-mediated induction of LDH. Some, if not all, of the molecular steps discussed in this paper may ultimately be recognized as part of a universal mechanism by which cAMP controls gene expression in higher eukaryotes. The idea of a functional role for cAMP-dependent protein kinase subunits in cAMP-mediated gene control has already had experimental support, but our identification of the regulatory subunit RII as a topoisomerase now more firmly points to a complex function for the kinase in regulating gene function at the DNA level. We look forward to the elucidation of the function of those nuclear proteins that serve as substrate for the catalytic subunit of cAMP-dependent protein kinase. Further studies related to the molecular interaction of RII with chromosomal DNA should be a fruitful area for future research.

Translocation of cAMP-dependent protein kinase to the nucleus during development of Dictyostelium discoideum

The distribution of the catalytic and regulatory subunits of the cAMP-dependent protein kinase between cytoplasm and nucleus was determined during the development of Dictyostelium discoideum. In vegetative amoebae approximately 2% of the subunits were in the nucleus. During development there was an approximately 5-fold increase in total soluble cAMP-dependent protein kinase and a 15- to 30-fold increase of enzyme in the nuclear fraction. There was a reverse translocation from nucleus to cytoplasm, when Tipped Aggregates were disrupted and the resultant amoebae incubated in single-cell suspension. The addition of cAMP to these single-cell suspensions brought about the reentry of the subunits into the nucleus. The findings are discussed in relation to the potential role of the cAMP-dependent protein kinase in the regulation of mRNA and protein synthesis.

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.

Cyclic AMP regulation of eukaryotic gene transcription by two discrete molecular mechanisms

In experiments designed to study the mechanism by which peptide hormones binding to their plasma membrane receptors stimulate the expression of specific genes, the transcription of two neuroendocrine genes, prolactin and growth hormone, was analyzed in a rat pituitary cell line. The results showed that cyclic adenosine monophosphate (cyclic AMP) stimulates the transcription of discrete subsets of eukaryotic genes by at least two independent molecular mechanisms. Cyclic AMP stimulated growth hormone gene transcription and phosphorylation of a 19,000-dalton nuclear protein; this appears to reflect direct nuclear actions of the cyclic AMP-dependent protein kinase. In contrast, the stimulation by cyclic AMP of prolactin gene transcription appears to reflect activation of a discrete calcium-dependent event.

Role of prostaglandins in hypoxia-stimulated erythropoietin production

The role of prostaglandins in the mediation of hypoxia-stimulated erythropoietin (Ep) production by cultured rat renal mesangial cells was examined. It was found that an increase in prostaglandin E2 (PGE2) production accompanied the rise in Ep due to hypoxia (2% O2). The hypoxia-stimulated increase in Ep production was abolished in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M). When PGE2 (10(-6) M was added simultaneously with indomethacin, however, no diminution in hypoxia-stimulated Ep production was observed. Addition of arachidonic acid (AA, 10(-5) M), PGE2 (10(-6) M), or PGI2 (10(-4) M) enhanced Ep production under normoxic conditions (20% O2), while PGF2 alpha (10(-6) M) had no effect on Ep production. AA, PGE2, and PGI2 were found to stimulate adenosine 3',5'-cyclic monophosphate formation by the cultured mesangial cells. Enhancement of adenylate cyclase activity by forskolin (10(-5) M) also increased Ep production in the cell cultures. Our results suggest that hypoxia-stimulated Ep production by cultured mesangial cells is mediated by prostaglandins with subsequent stimulation of adenylate cyclase activity.

Induction of myelin components: cyclic AMP increases the synthesis rate of 2',3'-cyclic nucleotide 3'-phosphohydrolase in C6 glioma cells

In an effort to determine the factors that stimulate myelin synthesis, we investigated the mechanism by which dibutyryl cyclic AMP induces the activity of the myelin enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP; EC 3.1.4.37), in C6 glioma cells. Immunotitration experiments and measurements of the accumulation of [35S]methionine-labeled CNP showed that dibutyryl cyclic AMP increased the amount of CNP in the cells but not the catalytic activity per molecule of the enzyme. Moreover, inhibition of protein synthesis with cycloheximide abolished induction of enzyme activity. Dibutyryl cyclic AMP doubled the rate of CNP synthesis but had no effect on the half-life of the enzyme (approximately 33 h). The induction was partially blocked by the inhibitors of mRNA synthesis, cordycepin or alpha-amanitin. Thus, cyclic AMP induces the synthesis of CNP.

A minireview of microheterogeneity in H1 histone and its possible significance

Subtypes of H1 histone vary in primary structure, and the higher organisms that have been studied each seem to have about a half-dozen subtypes. The proportions of these subtypes vary with the progress of differentiation as seen in embryonic development, hormonally induced changes, spermatogenesis, and terminal differentiation. The H1 subtypes differ among themselves in their ability to condense DNA and small chromatin fragments. They have the potential, therefore, of causing different parts of the chromatin to be condensed to different degrees.

Histones H3 and H4 inhibit protein kinase C specifically

The lysine-rich histone H1 is a preferred substrate for the Ca2+-phospholipid-dependent protein kinase (protein kinase C). Histones H3 and H4 are poor substrates but potent inhibitors of the enzyme. The inhibitory effect of H3 and H4 seems to result mainly from a decreased sensitivity of protein kinase C to stimulation by phosphatidylserine (PS). These observations suggest that site-specific phosphorylation of one histone type can be regulated by other histones.