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.     

Phosphorylation of rat C6 glioma cell DNA-dependent RNA polymerase II in vivo. Identification of phosphorylated subunits and modulation of phosphorylation by isoproterenol and N6,O2'-dibutyryl cyclic AMP

Evidence is presented that isoproterenol treatment of rat C6 glioma cells, under conditions that increase glioma cell cAMP levels, causes the phosphorylative modification of several RNA polymerase II subunits. RNA polymerase II in control and isoproterenol-stimulated 32Pi-labeled confluent glioma cells was immunoprecipitated from ribonuclease-treated nuclear extracts with hen anti-calf RNA polymerase II antiserum conjugated to Sepharose. The immunoprecipitated RNA polymerase II was analyzed for 32P-labeled subunits by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. Using this technique, we have shown that isoproterenol causes a time-dependent increase of phosphate incorporation into RNA polymerase II subunits of 214,000, 180,000, 140,000, 35,000, 28,000, and 16,500 daltons. Phosphate incorporation occurred exclusively on serine in all of the six subunits. About 0.5-2 mol of phosphate/mol of RNA polymerase II subunit were incorporated. Dibutyryl cAMP (10(-3)M) mimics the stimulatory action of isoproterenol and mediates increased phosphate incorporation into the six subunits. (RS)-propranolol (10(-4)M) prevents the isoproterenol-mediated phosphorylative changes. These data indicate that isoproterenol, via cAMP, mediates a transient structural modification of RNA polymerase II subunits in rat C6 glioma cells which may possibly lead to a modulation of RNA polymerase II function(s).     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Basolateral plasma membrane localization of ouabain-sensitive sodium transport sites in the secretory epithelium of the avian salt gland

The distribution of Na+ pump sites (Na+-K+-ATPase) in the secretory epithelium of the avian salt gland was demonstrated by freeze-dry autoradiographic analysis of [(3)H] ouabain binding sites. Kinetic studies indicated that near saturation of tissue binding sites occurred when slices of salt glands from salt-stressed ducks were exposed to 2.2 μM ouabain (containing 5 μCi/ml [(3)H]ouabain) for 90 min. Washing with label-free Ringer's solution for 90 min extracted only 10% of the inhibitor, an amount which corresponded to ouabain present in the tissue spaces labeled by [(14)C]insulin. Increasing the KCl concentration of the incubation medium reduced the rate of ouabain binding but not the maximal amount bound. In contrast to the low level of ouabain binding to salt glands of ducks maintained on a freshwater regimen, exposure to a salt water diet led to a more than threefold increase in binding within 9-11 days. This increase paralleled the similar increment in Na+-K+-ATPase activity described previously. [(3)H]ouabain binding sites were localized autoradiographically to the folded basolateral plasma membrane of the principal secretory cells. The luminal surfaces of these cells were unlabeled. Mitotically active peripheral cells were also unlabeled. The cell-specific pattern of [(3)H]ouabain binding to principal secretory cells and the membrane-specific localization of binding sites to the nonluminal surfaces of these cells were identical to the distribution of Na+-K+-ATPase as reflected by the cytochemical localization of ouabain-sensitive and K+-dependent nitrophenyl phosphatase activity. The relationship between the nonluminal localization of Na+-K+-ATPase and the possible role of the enzyme n NaCl secretion is considered in the light of physiological data on electrolyte transport in salt glands and other secretory epithelia.     

Ontogeny and multiplicity of cyclic AMP-dependent protein kinase in thymic lymphoid cells.

Cyclic adenosine 3′:5′-monophosphate-dependent protein kinases were studied in thymus lymphoid cells and were found to be similar to their counterparts in other tissues with respect to substrate preference and concentration dependence. A previously not identified, restrictive subcellular compartmentalization of the protein kinase isozymes was found: Type I was predominantly present in the nucleus of adult and juvenile human and rat thymus cells, whereas the type II kinase was restricted to the cytosol fraction of unstimulated cells. Additionally, a decline in the specific activity of protein kinase was progressive with increasing age of the animal and distinct from the general observation that lymphoid cell numbers decrease with age. These findings may be correlated with age-dependent immunodeficiencies and perhaps have functional significance in the regulatory role of protein phosphorylation in lymphoid cell activation.     

Cyclic AMP-dependent and -independent protein phosphokinase activity in subcellular fractions of synchronously growing leydig I-10 cells.

The Leydig I-10 tumor cell line was synchronized by the double thymidine block method using 1.0 mM thymidine. Protein phosphokinase activity of subcellular fractions was determined at various times throughout the cell cycle. Microsomal cAMP-independent kinase activity increased in G2 and decreased during the S and G1 phases. Except for relatively small increases during the G1 and late S phases, microsomal cAMP-dependent kinase activity remained unchanged throughout most of the cycle. In the lysosomal-mitochondrial fraction, cAMP-dependent and cAMP-independent protein kinase activity increased during the S phase. Independent kinase activity peaked again during G1, while the dependent kinase became depressed. Phosphokinase activity increased in the nuclear fraction in late G2 and during mitosis, and was due to increases in both cAMP-independent and cAMP-dependent kinase activity. Cytosol cAMP-dependent kinase activity increased in G2 and during mitosis; cAMP-independent kinase activity showed some increased activity during late G2 and mitosis. These temporal variations in the subcellular kinase activities throughout the cell cycle may act to phosphorylate subcellular protein substrates in a cell cycle-specific fashion.     

Studies on the binding of 1-anilino-8-naphthalene sulfonate to very low density and high density himan serum lipoproteins.

Very low density and high density lipoproteins have been isolated from human plasma and their interaction with 1-anilin0-8-naphthalene sulfonate has been studied under different conditions of pH and added salt. Intrinsic fluorescence of bound 1-anilino-8-naphthalene sulfonate was higher for high density lipoproteins then for very low density lipoproteins, but was unaffected by salt in both systems. Binding of 1-anilino-8-naphthalene sulfonate by both these lipoproteins was saturable and was higher in the presence of added NaCl or CaCl2, Ca2+ having a greater effect than Na+ in enhancing fluorescence. The binding data were analyzed by Scatchard plots; the number of binding sites and the affinity of 1-anilino-8-naphthalene sulfonate for the site increased with increasing salt concentration. Fluorescence pH curves were similar to those published for phospholipids. From these and previous observations it is suggested that the phospholipids probably represent the major binding sites for 1-anilino-8-naphthalene sulfonate.