Molecular cloning, cDNA structure and tissue-specific expression of the human regulatory subunit RI beta of cAMP-dependent protein kinases

Investigating PKA-RII specificity using analogs of the PKA:AKAP peptide inhibitor STAD-2

Generation of the second messenger molecule cAMP mediates a variety of cellular responses which are essential for critical cellular processes. In response to elevated cAMP levels, cAMP dependent protein kinase (PKA) phosphorylates serine and threonine residues on a wide variety of target substrates. In order to enhance the precision and directionality of these signaling events, PKA is localized to discrete locations within the cell by A-kinase anchoring proteins (AKAPs). The interaction between PKA and AKAPs is mediated via an amphipathic α-helix derived from AKAPs which binds to a stable hydrophobic groove formed in the dimerization/docking (D/D) domain of PKA-R in an isoform-specific fashion. Although numerous AKAP disruptors have previously been identified that can inhibit either RI- or RII-selective AKAPs, no AKAP disruptors have been identified that have isoform specificity for RIα versus RIβ or RIIα versus RIIβ. As a strategy to identify isoform-specific AKAP inhibitors, a library of chemically stapled protein-protein interaction (PPI) disruptors was developed based on the RII-selective AKAP disruptor, STAD-2. An alanine was substituted at each position in the sequence, and from this library it was possible to delineate the importance of longer aliphatic residues in the formation of a region which complements the hydrophobic cleft formed by the D/D domain. Interestingly, lysine residues that were added to both terminal ends of the peptide sequence to facilitate water solubility appear to contribute to isoform specificity for RIIα over RIIβ while having only weak interaction with RI. This work supports current hypotheses on the mechanisms of AKAP binding and highlights the significance of particular residue positions that aid in distinguishing between the RII isoforms and may provide insight into future design of isoform-selective AKAP disruptors.

Pituitary adenoma nitroproteomics: current status and perspectives

Oxidative stress is extensively associated with tumorigenesis. A series of studies on stable tyrosine nitration as a marker of oxidative damage were performed in human pituitary and adenoma. This paper reviews published research on the mass spectrometry characteristics of nitropeptides and nitroproteomics of pituitary controls and adenomas. The methodology used for nitroproteomics, the current status of human pituitary nitroproteomics studies, and the future perspectives are reviewed. Enrichment of those low-abundance endogenous nitroproteins from human tissues or body fluid samples is the first important step for nitroproteomics studies. Mass spectrometry is the essential approach to determine the amino acid sequence and locate the nitrotyrosine sites. Bioinformatics analyses, including protein domain and motif analyses, are needed to locate the nitrotyrosine site within the corresponding protein domains/motifs. Systems biology techniques, including pathway analysis, are necessary to discover signaling pathway networks involving nitroproteins from the systematically global point of view. Future quantitative nitroproteomics will discover pituitary adenoma-specific nitroprotein(s). Structural biology techniques such as X-ray crystallography analysis will solidly clarify the effects of tyrosine nitration on structure and functions of a protein. Those studies will eventually address the mechanisms and biological functions of tyrosine nitration in pituitary tumorigenesis and will discover nitroprotein biomarkers for pituitary adenomas and targets for drug design for pituitary adenoma therapy.

Localization and quaternary structure of the PKA RIβ holoenzyme

Specificity for signaling by cAMP-dependent protein kinase (PKA) is achieved by both targeting and isoform diversity. The inactive PKA holoenzyme has two catalytic (C) subunits and a regulatory (R) subunit dimer (R(2):C(2)). Although the RIα, RIIα, and RIIβ isoforms are well studied, little is known about RIβ. We show here that RIβ is enriched selectively in mitochondria and hypothesized that its unique biological importance and functional nonredundancy will correlate with its structure. Small-angle X-ray scattering showed that the overall shape of RIβ(2):C(2) is different from its closest homolog, RIα(2):C(2). The full-length RIβ(2):C(2) crystal structure allows us to visualize all the domains of the PKA holoenzyme complex and shows how isoform-specific assembly of holoenzyme complexes can create distinct quaternary structures even though the R(1):C(1) heterodimers are similar in all isoforms. The creation of discrete isoform-specific PKA holoenzyme signaling "foci" paves the way for exploring further biological roles of PKA RIβ and establishes a paradigm for PKA signaling.

CK2-mediated phosphorylation of a type II regulatory subunit of cAMP-dependent protein kinase from the mollusk Mytilus galloprovincialis

Two isoforms of regulatory (R) subunit of cAMP-dependent protein kinase (PKA), named R(myt1) and R(myt2), were identified so far in the sea mussel Mytilus galloprovincialis. Out of them, only R(myt2) was phosphorylated in vitro by casein kinase 2 (CK2) using GTP as phosphate donor. CK2 catalytic subunit (CK2alpha) itself was sufficient to phosphorylate R(myt2), but phosphorylation was enhanced by the presence of the regulatory subunit CK2beta. Even in the absence of CK2, R(myt2) was phosphorylated to a certain extent when it was incubated with GTP. This basal phosphorylation was partially abolished by the known inhibitors apigenin and emodin, which suggests the presence of a residual amount of endogenous CK2 in the preparation of purified R subunit. CK2-mediated phosphorylation significantly decreases the ability of R(myt2) to inhibit PKA catalytic (C) subunit activity in the absence of cAMP. On the other hand, the sequence of several peptides obtained from the tryptic digestion of R(myt2) showed that mussel protein contains the signature sequence common to all PKA family members, within the "phosphate binding cassette" (PBC) A and B. Moreover, the degree of identity between the sequences of peptides from R(myt2), as a whole, and those from type II R subunits was 68-75%, but the global identity percentage with type I R subunits was only about 30%, so that R(myt2) can be classified as a type II R subunit.

Nitroproteins from a human pituitary adenoma tissue discovered with a nitrotyrosine affinity column and tandem mass spectrometry

The aim of this study was to characterize endogenous nitroproteins, and those proteins that interact with nitroproteins, in a human pituitary nonfunctional adenoma so as to clarify the role of protein nitration in adenomas. A nitrotyrosine affinity column (NTAC) was used to preferentially enrich and isolate endogenous nitroproteins and nitroprotein-protein complexes from a tissue homogenate that was prepared from a human pituitary nonfunctional pituitary adenoma. The preferentially enriched endogenous nitroproteins and nitroprotein-protein complexes were subjected to trypsin digestion, desalination, and tandem mass spectrometry analysis. Nine nitroproteins (Rho-GTPase-activing protein 5, leukocyte immunoglobulin-like receptor subfamily A member 4 precursor, zinc finger protein 432, cAMP-dependent protein kinase type I-beta regulatory subunit, sphingosine-1-phosphate lyase 1, centaurin beta 1, proteasome subunit alpha type 2, interleukin 1 family member 6, and rhophilin 2) and three proteins (interleukin 1 receptor-associated kinase-like 2, glutamate receptor-interacting protein 2, and ubiquitin) that interacted with nitroproteins were discovered. The nitration site of each nitroprotein was located onto the functional domain where nitration occurred, and each nitroprotein was related to a corresponding functional system. Those data indicate that protein nitration might be an important molecular event in the formation of a human pituitary nonfunctional adenoma.

Characterization of the NF2 protein merlin and the ERM protein ezrin in human, rat, and mouse central nervous system

The neurofibromatosis 2 (NF2) protein, merlin, is structurally related to the ERM (ezrin-radixin-moesin) protein family of membrane-cytoskeleton linkers and is mutated in nervous system tumors. Apart from tumor suppressor activity, merlin's functions are poorly understood. We compared the localization and expression of merlin and ezrin in developing and adult brain and in brain-derived progenitor cells. Both proteins were widely but differentially expressed in human, rat, and mouse brain. In brain tissue and neuronal progenitor cell cultures merlin was predominantly found in neurons while ezrin was expressed in astrocytes. Merlin expression was seen from E11 in mouse embryos, whereas ezrin was present earlier. Both proteins were expressed in embryonic mouse neurospheres, where ezrin was specifically localized in filopodia of adherent neuronal progenitor cells. Subcellular analysis demonstrated ezrin in fine filopodial structures in astrocytes, while merlin was detected in neuronal synaptic junctions. The widespread expression of merlin in brain and its association with protein kinase A suggest a role for merlin in brain biology.

Isoforms of cAMP-dependent protein kinase in the bivalve mollusk Mytilus galloprovincialis: activation by cyclic nucleotides and effect of temperature

Two different isoforms of cAMP-dependent protein kinase (PKA) have been partially purified from the posterior adductor muscle and the mantle tissue of the sea mussel Mytilus galloprovincialis. The holoenzymes contain as regulatory subunit (R) the previously identified isoforms Rmyt1 and Rmyt2, and were named PKAmyt1 and PKAmyt2, respectively. Both cAMP and cGMP can activate these PKA isoforms completely, although they exhibit a sensitivity approximately 100-fold higher for cAMP than for cGMP. When compared to PKAmyt2, the affinity of PKAmyt1 for cAMP and cGMP is 2- and 3.5-fold higher, respectively. The effect of temperature on the protein kinase activity of both PKA isoforms was examined. Temperature changes did not affect significantly the apparent activation constants (Ka) for cAMP. However, the protein kinase activity was clearly modified and a remarkable difference was observed between both PKA isoforms. PKAmyt1 showed a linear Arrhenius plot over the full range of temperature tested, with an activation energy of 15.3+/-1.5 kJ/mol. By contrast, PKAmyt2 showed a distinct break in the Arrhenius plot at 15 degrees C; the activation energy when temperature was above 15 degrees C was 7-fold higher than that of lower temperatures (70.9+/-8.1 kJ/mol vs 10.6+/-6.5 kJ/mol). These data indicate that, above 15 degrees C, PKAmyt2 activity is much more temperature-dependent than that of PKAmyt1. This different behavior would be related to the different role that these isoforms may play in the tissues where they are located.

Genomic structure of the human gene for protein kinase A regulatory subunit R1-beta (PRKAR1B) on 7p22: no evidence for mutations in familial hyperaldosteronism type II in a large affected kindred

OBJECTIVE

Familial hyperaldosteronism type II (FH-II) is characterized by inheritance of primary aldosteronism (PAL) but, unlike FH-I, is not glucocorticoid remediable and not associated with the hybrid CYP11B1/CYP11B2 gene mutation. Analysis of two pedigrees previously demonstrated linkage of FH-II with a locus at chromosome 7p22. We sought to determine whether mutations in the exons or intron/exon boundaries in PRKAR1B (encoding protein kinase A regulatory subunit R1-beta), which resides within the linked locus, are associated with FH-II.

METHODS

Primers enabling sequencing of all exons and intron/exon boundaries were designed by BLAT search using known mRNA sequence, and comparison with an orthologous mouse gene. Sequences from four affected and two unaffected subjects from an Australian family with FH-II demonstrating linkage at 7p22 were compared with published sequences.

RESULTS

A probable two-nucleotide GenBank sequence error, resulting in an amino acid change, was detected. Two of seven single nucleotide polymorphisms (SNPs) identified were in exons and five in introns. Neither exon-localized SNP resulted in an amino acid change. All intron-localized SNPs were at least 16 nucleotides from the closest intron/exon boundary and therefore unlikely to interfere with gene splicing. Importantly, none of the identified SNPs was exclusively associated with affectation status.

CONCLUSIONS

Mutations in the exons or intron/exon boundaries of PRKAR1B do not appear to be responsible for FH-II in this family, but a mutation in the promoter or remaining intronic or 5' or 3' untranslated regions could be. Alternatively, a mutation within another gene residing at the 7p22 locus may be responsible.

Merlin links to the cAMP neuronal signaling pathway by anchoring the RIbeta subunit of protein kinase A

The cAMP-protein kinase A (PKA) pathway, important in neuronal signaling, is regulated by molecules that bind and target PKA regulatory subunits. Of four regulatory subunits, RIbeta is most abundantly expressed in brain. The RIbeta knockout mouse has defects in hippocampal synaptic plasticity, suggesting a role for RIbeta in learning and memory-related functions. Molecules that interact with or regulate RIbeta are still unknown. We identified the neurofibromatosis 2 tumor suppressor protein merlin (schwannomin), a molecule related to the ezrin-radixin-moesin family of membrane-cytoskeleton linker proteins, as a binding partner for RIbeta. Merlin and RIbeta demonstrated a similar expression pattern in central nervous system neurons and an overlapping subcellular localization in cultured hippocampal neurons and transfected cells. The proteins were coprecipitated from brain lysates by cAMP-agarose and coimmunoprecipited from cellular lysates with specific antibodies. In vitro binding studies verified that the interaction is direct. The interaction appeared to be under conformational regulation and was mediated via the alpha-helical region of merlin. Sequence comparison between merlin and known PKA anchoring proteins identified a conserved alpha-helical PKA anchoring protein motif in merlin. These results identify merlin as the first neuronal binding partner for PKA-RIbeta and suggest a novel function for merlin in connecting neuronal cytoskeleton to PKA signaling.

Characterization of a type I regulatory subunit of cAMP-dependent protein kinase from the bivalve mollusk Mytilus galloprovincialis

Two isoforms of the regulatory subunit (R) of cAMP-dependent protein kinase (PKA), named R(myt1) and R(myt2), had been purified in our laboratory from two different tissues of the sea mussel Mytilus galloprovincialis. In this paper, we report the sequences of several peptides obtained from tryptic digestion of R(myt1). As a whole, these sequences showed high homology with regions of type I R subunits from invertebrate and also from mammalian sources, but homology with those of fungal and type II R subunits was much lower, which indicates that R(myt1) can be considered as a type I R isoform. This conclusion is also supported by the following biochemical properties: (1) R(myt1) was proved to have interchain disulfide bonds stabilizing its dimeric structure; (2) it failed to be phosphorylated by the catalytic (C) subunit purified from mussel; (3) it has a higher pI value than that of the R(myt2) isoform; and (4) it showed cross-reactivity with mammalian anti-RIbeta antibody.

Activation of the cAMP-dependent protein kinase signaling pathway by luteinizing hormone in trout theca layers

In the fish ovary, LH is the main factor regulating the production of steroids during the periovulatory period and its effects are believed to be mediated, at least partially, through the cAMP-dependent protein kinase (PKA) signaling pathway. However, there is no direct evidence for the presence of PKA in the fish ovary nor on the regulation of its activity by fish LH. Here, we show the identification of regulatory (R) and catalytic (C) subunits of PKA in trout theca cells by immunoblotting. DEAE-cellulose chromatography of theca cell extracts indicated the presence of PKA type I and II and showed that trout theca cells display PKA-specific phosphotransferase and cAMP-binding activities. Salmon LH (sLH) stimulated PKA activity and increased the levels of immunoreactive RIIalpha, RIIbeta and C subunits in trout theca layers. These observations, coupled with the sLH-dependent decrease in the half-life of the C subunit, as shown by pulse-chase experiments, strongly suggest that sLH activates PKA in trout theca cells. Furthermore, our results suggest that ovarian PKA activity and its regulation by LH has been well conserved from fish to humans.

Human myometrial quiescence and activation during gestation and parturition involve dramatic changes in expression and activity of particulate type II (RII alpha) protein kinase A holoenzyme

There are substantial data indicating that components of the cAMP-signaling pathway are differentially expressed in the human myometrium during pregnancy. The effects of cAMP in most tissues and cell types are mainly modulated via protein kinase A, a heterotetrameric protein complex consisting of two regulatory (R) and two catalytic (C) subunits. In the studies presented here, we used specific antibodies in Western blotting/immunoprecipitation, RT-PCR, and functional protein kinase A (PKA) phosphorylation assays to determine the PKA holoenzymes that are expressed in the human myometrium throughout pregnancy and labor. We report that as early as the second trimester of pregnancy, there is a significant increase in expression of the regulatory RII alpha protein subunit of PKA in the myometrium. This increase in protein expression is also mirrored at the mRNA level, indicating transcriptional control throughout pregnancy, whereas during parturition both transcript and protein are significantly decreased. This increase in RII alpha protein also resulted in increased particulate PKA activity in the myometrium during gestation, which was subsequently decreased during labor. Two specific A kinase anchoring proteins, AKAP95 and AKAP79, which have high binding affinities for RII alpha subunits, were found to form complexes with myometrial RII alpha species employing immunoprecipitation assays, but their levels of expression remained uniform in all myometrial tissue samples investigated. Our findings indicate that increased particulate type II PKA activity occurs throughout pregnancy, therefore directing the cAMP quiescence signal to specific subcellular loci within myometrial smooth muscle cells including the contractile machinery at the cytoskeleton; this effect is then removed during parturition.

A kinase anchoring protein (AKAP) interaction and dimerization of the RIalpha and RIbeta regulatory subunits of protein kinase a in vivo by the yeast two hybrid system

Protein kinase A (PKA) regulatory (R) subunits dimerize through an N-terminal motif. Such dimerization is necessary for binding to PKA anchoring proteins (AKAPs) and targeting of PKA to its site of action. In the present study, we used the yeast two-hybrid system as an in vivo bio-reporter assay and analyzed the formation of homo- and heterodimeric complexes of RIalpha and RIbeta as well as AKAP binding of RI dimers. Native polyacrylamide gel electrophoresis (PAGE) of yeast extracts confirmed the two-hybrid data. Both RIalpha- and RIbeta homodimers as well as an RIalpha:RIbeta heterodimer were observed. Single, double and one triple mutation were introduced into the RIalpha and RIbeta subunits and dimerization properties of the mutants were analyzed. Consistent with previous reports, RIalpha(C37H) dimerized, although the disulfide bridges were disrupted, whereas the additional mutation of F47 or F52 abolished the dimerization. Corresponding mutations (C38H, F48A, F53A) in RIbeta were not sufficient to abolish the RIbeta dimerization, indicating that additional or other amino acids are important. RIalpha:RIbeta heterodimers of the mutants were formed at intermediate stringency. Analysis of ternary complexes by the yeast two-hybrid system revealed that RIalpha and RIbeta homodimers as well as an RIalpha:RIbeta heterodimer and several of the mutants were able to bind to the R-binding domain of AKAP149/D-AKAP1. Furthermore, an RIbeta:AKAP149 complex was identified following introduction of RIbeta into HEK293 cells. Importantly, RIbeta revealed AKAP binding properties similar to those of RIalpha, indicating that RIbeta holoenzymes may be anchored.

A conserved serine juxtaposed to the pseudosubstrate site of type I cGMP-dependent protein kinase contributes strongly to autoinhibition and lower cGMP affinity

Serines 64 and 79 are homologous residues that are juxtaposed to the autoinhibitory pseudosubstrate site in cGMP-dependent protein kinase type Ialpha and type Ibeta (PKG-Ialpha and PKG-Ibeta), respectively. Autophosphorylation of this residue is associated with activation of type I PKGs. To determine the role of this conserved serine, point mutations have been made in PKG-Ialpha (S64A, S64T, S64D, and S64N) and PKG-Ibeta (S79A). In wild-type PKG-Ialpha, basal kinase activity ratio (-cGMP/+cGMP) is 0.11, autophosphorylation increases this ratio 3-fold, and the K(a) and K(D) values for cGMP are 127 and 36 nm, respectively. S64A PKG-Ialpha basal kinase activity ratio increases 2-fold, cGMP binding affinity increases approximately 10-fold in both K(a) and K(D), and activation by autophosphorylation is slight. S64D and S64N mutants are nearly constitutively active in the absence of cGMP, cGMP binding affinity in each increases 18-fold, and autophosphorylation does not affect the kinase activity of these mutants. Mutation of the homologous site in PKG-Ibeta (S79A) increases the basal kinase activity ratio 2-fold and cGMP binding affinity 5-fold over that of wild-type PKG-Ibeta. The combined results demonstrate that a conserved serine juxtaposed to the pseudosubstrate site in type I PKGs contributes importantly to enzyme function by increasing autoinhibition and decreasing cGMP binding affinity.

Electrical muscle activity pattern and transcriptional and posttranscriptional mechanisms regulate PKA subunit expression in rat skeletal muscle

We have examined protein kinase A (PKA) subunit expression in adult rat skeletal muscles. Northern blots identified PKA catalytic alpha and regulatory (R) I alpha and RII alpha subunits as the major subunits expressed in slowly contracting soleus (SOL) and rapidly contracting extensor digitorum longus (EDL) muscles. In addition, the steady-state RNA levels of PKA subunit mRNAs and activities of RI alpha and RII alpha promoters are similar in SOL and EDL. These data indicate that posttranscriptional mechanisms account for the twofold differences in PKA subunit protein levels reported earlier. Electrical stimulation of denervated SOL with an EDL-like activity pattern (fast pattern) transformed SOL into an EDL-like muscle with regard to PKA protein levels. These experiments suggest that the posttranscriptional regulation is activity pattern-dependent. Denervation specifically increased RI alpha promoter activity and RI alpha mRNA levels in SOL and EDL. Further experiments indicated that the RI alpha 1a upstream sequences were activated following denervation. Direct electrical stimulation prevented the rise in RI alpha mRNA levels following denervation, demonstrating that electrical muscle activity regulates transcription.

Cold-stimulated increase in a regulatory subunit of cAMP-dependent protein kinase in human hepatoblastoma cells

Although cold-stress responses in bacteria and plants have been well studied and hypothermic conditions are used in clinical treatments, there has been little investigation of cold-stress responses in human cells, and there has been no report on the involvement of signal transduction modulators in the cold-stress response in human cells. We therefore investigated alterations in the expression of genes involved in the signal transduction system and the mechanisms of cold-stimulated increases in the expression of genes in human hepatoblastoma (HepG2) cells. Using a cDNA expression array method, we found that a transcript encoding a regulatory subunit Ibeta (RIbeta) of cyclic AMP-dependent protein kinase (PKA) was increased in cold-stressed cells. Western blot analysis revealed that the amount of PKA RIbeta protein was increased by cold treatment, while that of a PKA catalytic subunit (C) was unchanged. The protein level of PKA RIbeta was increased in cells treated with low concentrations of actinomycin D, whereas that of PKA C was not, implying that the increase was caused by the suppression of transcription at low temperatures. In addition, degradation of the PKA RIbeta protein was not stimulated by cold treatment, unlike that of the PKA C protein. The results suggest that signal transduction through PKA also participates in cold-stress responses in human cells and that multiple mechanisms are involved in the increase in the level of the PKA RIbeta protein.

Protein kinase A RI beta subunit deficiency in lupus T lymphocytes: bypassing a block in RI beta translation reconstitutes protein kinase A activity and augments IL-2 production

A profound deficiency of type I protein kinase A (PKA-I or RIalpha/beta2C2) phosphotransferase activity occurs in the T lymphocytes of 80% of subjects with systemic lupus erythematosus (SLE), an autoimmune disorder of unknown etiology. This isozyme deficiency is predominantly the product of reduced or absent beta isoform of the type I regulatory subunit (RIbeta). Transient transfection of RIbeta cDNAs from SLE subjects into autologous T cells that do not synthesize the RIbeta subunit bypassed the block, resulting in RIbeta subunit synthesis and restoration of the PKA-Ibeta (RIbeta2C2) holoenzyme. Transfected T cells activated via the T cell surface receptor complex revealed a significant increase of cAMP-activatable PKA activity that was associated with a significant increase in IL-2 production. These data demonstrate that a disorder of RIbeta translation exists, and that correction of the PKA-I deficiency may enhance T lymphocyte effector functions in SLE.

Novel alternatively spliced mRNA (1c) of the protein kinase A RIα subunit is implicated in haploid germ cell specific expression

By using 5' RACE on rat testis cDNA we identified three alternatively spliced mRNAs of the RIalpha subunit of cAMP-dependent protein kinase that differed in their 5' untranslated regions. Two of these 5'-regions showed similarity with the human RIalpha exons 1a and 1b, while the third (1c) constituted a novel mRNA splice variant. Northern blot analysis showed that the 1c mRNA was specifically expressed in testis and only in postmeiotic germ cells. In contrast, the RIalpha 1b and RIalpha 1a mRNAs were present both in premeiotic germ cells and somatic cells of the testis, and the expression of both RIalpha 1a and 1b mRNAs were stimulated by cAMP in Sertoli cells. In sperm, the RIalpha protein was expressed after meiosis, and targeted to various subcellular structures via anchoring proteins. The RIalpha 1c haploid-specific mRNA, therefore, may be important for the regulation of RIalpha expression in sperm.

Participation of type II protein kinase A in the retinoic acid-induced growth inhibition of SH-SY5Y human neuroblastoma cells

To examine the role of protein kinase A (EC 2.7.1.37) isozymes in the retinoic acid-induced growth inhibition and neuronal differentiation, we investigated the changes of protein kinase A isozyme patterns in retinoic acid-treated SH-SY5Y human neuroblastoma cells. Retinoic acid induced growth inhibition and neuronal differentiation of SH-SY5Y cells in a dose- and time-dependent manner. Neuronal differentiation was evidenced by extensive neurite outgrowth, decrease of N-Myc oncoprotein, and increase of GAP-43 mRNA. Type II protein kinase A activity increased by 1.5-fold in differentiated SH-SY5Y cells by retinoic acid treatment. The increase of type II protein kinase A was due to the increase of RIIbeta and Calpha subunits. Since type II protein kinase A and RIIbeta have been known to play important role(s) in the growth inhibition and differentiation of cancer cells, we further investigated the role of the increased type II protein kinase A by overexpressing RIIbeta in SH-SY5Y cells. The growth of RIIbeta-overexpressing cells was slower than that of parental cells, being comparable to that of retinoic acid-treated cells. Retinoic acid treatment further increased the RIIbeta level and further inhibited the growth of RIIbeta-overexpressing cells, showing strong correlation between the level of RIIbeta and growth inhibition. However, RIIbeta-overexpressing cells did not show any sign of neuronal differentiation and responded to retinoic acid in the same way as parental cells. These data suggest that protein kinase A participates in the retinoic acid-induced growth inhibition through the up-regulation of RIIbeta/type II protein kinase A.

Diminished Levels of Protein Kinase A RIα and RIβ Transcripts and Proteins in Systemic Lupus Erythematosus T Lymphocytes

Deficient type I protein kinase A phosphotransferase activity occurs in the T cells of 80% of subjects with systemic lupus erythematosus (SLE). To investigate the mechanism of this deficient isozyme activity, we hypothesized that reduced amounts of type I regulatory (RI) isoform transcripts, RIα and RIβ, may be associated with a diminution of RIα and/or RIβ protein. Sixteen SLE subjects with a mean (±1 SD) SLE disease activity index of 12.4 ± 7.2 were studied. Controls included 16 normal subjects, six subjects with primary Sjögren’s syndrome (SS), and three subjects with SS/SLE overlap. RT-PCR revealed that normal, SS, SS/SLE, and SLE T cells expressed mRNAs for all seven R and catalytic (C) subunit isoforms. Quantification of mRNAs by competitive PCR revealed that the ratio of RIα mRNA to RIβ mRNA in normal T cells was 3.4:1. In SLE T cells there were 20 and 49% decreases in RIα and RIβ mRNAs (RIβ; p = 0.008), respectively, resulting in an RIα:RIβ mRNA of 5.3:1. SS/SLE T cells showed a 72.5% decrease in RIβ mRNA compared with normal controls (p = 0.01). Immunoblotting of normal T cell RIα and RIβ proteins revealed a ratio of RIα:RIβ of 3.2:1. In SLE T cells, there was a 30% decrease in RIα protein (p = 0.002) and a 65% decrease in RIβ protein (p < 0.001), shifting the ratio of RIα:RIβ protein to 6.5:1. T cells from 25% of SLE subjects lacked any detectable RIβ protein. Analysis of several lupus T cell lines demonstrated a persistent deficiency of both proteins, excluding a potential effect of disease activity. In conclusion, reduced expression of RIα and RIβ transcripts is associated with a decrement in RIα and RIβ proteins and may contribute to deficient type I protein kinase A isozyme activity in SLE T cells.

Type II cAMP-dependent protein kinase regulates electrogenic ion transport in rabbit collecting duct

cAMP mediates many of the effects of vasopressin, prostaglandin E2, and beta-adrenergic agents upon salt and water transport in the renal collecting duct. The present studies examined the role of cAMP-dependent protein kinase (PKA) in mediating these effects. PKA is a heterotetramer comprised of two regulatory (R) subunits and two catalytic (C) subunits. The four PKA isoforms may be distinguished by their R subunits that have been designated RIalpha, RIbeta, RIIalpha, and RIIbeta. Three regulatory subunits, RIalpha, RIIalpha, and RIIbeta, were detected by immunoblot and ribonuclease protection in both primary cultures and fresh isolates of rabbit cortical collecting ducts (CCDs). Monolayers of cultured CCDs grown on semipermeable supports were mounted in an Ussing chamber, and combinations of cAMP analogs that selectively activate PKA type I vs. PKA type II were tested for their effect on electrogenic ion transport. Short-circuit current (Isc) was significantly increased by the PKA type II-selective analog pairs N6-monobutyryl-cAMP plus 8-(4-chlorophenylthio)-cAMP or N6-monobutyryl-cAMP plus 8-chloro-cAMP. In contrast the PKA type I-selective cAMP analog pair [N6-monobutyryl-cAMP plus 8-(6-aminohexyl)-amino-cAMP] had no effect on Isc. These results suggest PKA type II is the major isozyme regulating electrogenic ion transport in the rabbit collecting duct.

Cyclic-AMP-dependent protein kinase (PKA) in testicular cells. Cell specific expression, differential regulation and targeting of subunits of PKA

LH and FSH regulate via cyclic adenosine 3'5' cyclic monophosphate (cAMP) and cAMP-dependent protein kinase (PKA), steroid biosynthesis is Leydig and Sertoli cells, respectively. Cyclic AMP also regulates a number of different cellular processes such as cell growth and differentiation, ion channel conductivity, synaptic release of neurotransmitters, and gene transcription. The principle intracellular target for cAMP in mammalian cells is the PKA. The fact that this broad specificity protein kinase mediates a number of discrete physiological responses following cAMP engagement, has raised the question of how specificity is maintained in the cAMP/PKA system. Here we describe features of this signaling pathway that may contribute to explain how differential effects of cAMP may be contributed to features of the PKA signaling pathway.

Purification of a novel isoform of the regulatory subunit of cAMP-dependent protein kinase from the bivalve mollusk Mytilus galloprovincialis

Cytosolic extracts from the posterior adductor muscle of the bivalve mollusk Mytilus galloprovincialis contain significant amounts of both cGMP-binding and cGMP-stimulated protein kinase activities. However, photoaffinity labeling with 8-azido-[32P]cGMP revealed only a major cGMP-binding protein with an apparent molecular mass of 54 kDa (p54), lacking protein kinase activity itself. Instead, the purified and cGMP-free p54 protein has the ability to inhibit a mussel protein kinase homologous to the mammalian cAMP-dependent protein kinase (cAPK) catalytic subunit, the inhibition being relieved by cAMP or cGMP, which suggests that it can act as a regulatory subunit of cAPK. However, p54 failed to be recognized by a specific antibody against the regulatory subunit (type RII) previously isolated from mussel. Therefore, p54 must be a novel isoform of cAPK regulatory subunit that seems to have high affinity for both cGMP and cAMP.

Isozymes of cyclic AMP-dependent protein kinases (PKA) in human lymphoid cell lines: levels of endogenous cAMP influence levels of PKA subunits and growth in lymphoid cell lines

Activation of the cAMP signaling pathway in lymphoid cells is known to inhibit cell proliferation of T and B cells as well as cytotoxicity of natural killer (NK) cells. In order to find suitable model systems to study cAMP-mediated processes, we have examined the expression of cAMP-dependent protein kinase (PKA), endogenous levels of cAMP, and cell proliferation in eight cell lines of B lineage origin, four cell lines of T lineage origin, and normal human B and T cells. We demonstrated that the expression of mRNA and protein for one of the regulatory (R) subunits of PKA (RIalpha) was present in all the cells investigated, in contrast to the other R subunits (RIbeta, RIIalpha, and RIIbeta). Furthermore, three T cell lines and one B cell line expressed only RIalpha and C, implying these cells to contain solely PKA type I. Moreover, for the RI subunit, we observed an apparent reciprocal relationship between levels of mRNA and protein. Generally, RIalpha protein was low in cell lines where mRNA was elevated and vice versa. This was not the case for the RII subunits, where high levels of mRNA were associated with elevated levels of protein. Interestingly, we demonstrated an inverse correlation between levels of endogenous cAMP and cell growth as determined by [3H]-thymidine incorporation and cell-doubling rate (P < 0.05). Taken together, our results demonstrate great differences in PKA isozyme composition, which should be taken into consideration when using lymphoid cell lines as model system for cAMP/PKA effects in normal lymphocytes.

Cyclic AMP-dependent protein kinases and human trophoblast cell differentiation in vitro

Human trophoblast cells offer a unique in vitro model for the study of aspects of the dynamic processes occurring during cell fusion and syncytium formation. In the human placenta, mononuclear cytotrophoblasts aggregate and fuse to form a multinucleated syncytiotrophoblast. In vitro, the addition of cyclic AMP analogs, 8-bromo-cyclic-AMP or Sp-8-bromo-cyclic AMPS, promotes syncytiotrophoblast formation, as shown by the disappearance of immunostained E-cadherin and desmoplakin, and increased numbers of nuclei per syncytium. An antagonist of cyclic AMP, Rp-8-bromo-cyclic AMPS, and an inhibitor of the cyclic AMP-dependent protein kinase catalytic subunit, H-89, impair cell fusion. This led us to study the pattern of expression and subcellular localization of cyclic-AMP-dependent protein kinase subunits during syncytium formation. Cytotrophoblasts expressed the RIalpha and RIIalpha regulatory subunits and the Calpha and Cbeta catalytic subunits. RIalpha was down-regulated during syncytium formation. No change in RIIalpha protein levels was observed, but there was a drastic subcellular redistribution. RIIalpha located in the Golgi-centrosomal area of cytotrophoblasts was scattered throughout the cytoplasm of the syncytiotrophoblast. Interestingly, an accumulation of RIIalpha was observed underneath the apical membrane of syncytiotrophoblast in vitro and in situ. This suggests a key role of cyclic AMP-dependent protein kinase type IIalpha during cell fusion and microvilli formation, both of which are essential for the secretory and transfer functions of the syncytiotrophoblast.

PEST sequences in proteins involved in cyclic nucleotide signalling pathways

There is growing evidence that PEST sequences act as proteolytic recognition signals within polypeptides. PEST sequences are rich in proline (P), glutamic acid (E), serine (S), and threonine (T) and can be identified by the PEST-FIND program. Both the catalytic and regulatory subunits of the cAMP-dependent protein kinase have been shown to have conditional PEST sequences which are exposed upon cAMP binding to the enzyme. cAMP binding leads to rapid dissociation of C- and R-subunits, and both subunits have increased sensitivity to proteolysis. It is not known whether other proteins that participate in the cyclic nucleotide signalling pathway have PEST regions in their amino acid sequences. Therefore, we have screened amino acid sequences of proteins that are directly involved in cyclic nucleotide cascade, including cGMP-dependent protein kinases, anchoring proteins for cAMP-dependent protein kinase, cyclic nucleotide-gated ion channels, and cyclic nucleotide phosphodiesterases, for PEST sequences using the PEST-FIND program. Many PEST sequences with high scores have been identified in these proteins. The occurrence of the PEST sequences is very high in proteins involved in cyclic nucleotide signalling pathways (approximately 80%). This value is much higher than the percentage (10%) of PEST sequences that can be found in the primary structures of the proteins listed in the data bank. This frequent occurrence of PEST sequences in proteins involved in cyclic nucleotide action and metabolism suggests an important role of proteolysis of these key proteins of signal transduction.

Structure, function, and regulation of human cAMP-dependent protein kinases

A large number of hormones, neurotransmitters, and other signaling substances that bind to G-protein-coupled cell-surface receptors have their signals converge at one sole second messenger, cAMP. The question of how specificity can be maintained in a signal-transduction system in which many extracellular signals leading to a vast array of intracellular responses are all mediated through one second-messenger system has been the subject of thorough investigation and a great deal of speculation. An increasing number of cAK isozymes, consisting of homo- or heterodimers of R subunits (RIalpha, RIbeta, RIIalpha, RIIbeta) with associated catalytic subunits (C alpha, Cbeta, Cgamma), may, at least in part, explain this specificity. The various cAK isozymes display distinct biochemical properties, and the heterogeneous subunits of cAK reveal cell-specific expression and differential regulation at the level of gene transcription, mRNA stability, and protein stability in response to a wide range of hormones and other signaling substances. The existence of a number of anchoring proteins specific to either RIIalpha or RIIbeta, and which localize cAKII isozymes toward distinct substrates at defined subcellular loci, strongly supports the idea that specific functions can be assigned to the various cAK isozymes. The demonstration that selective activation of cAKI is necessary and sufficient for cAMP-mediated inhibition of T-cell proliferation, and the observation that T-cell activation is associated with redistribution and colocalization of cAKI to the TCR, is also compatible with the notion of isozyme-specific effects.

Type II protein kinase A up-regulation is sufficient to induce growth inhibition in SK-N-SH human neuroblastoma cells

We have previously reported that overexpression of RII beta subunit of protein kinase A, which markedly reduces RI alpha protein, induces growth inhibition in SK-N-SH human neuroblastoma cells. To determine whether the reduction of RI alpha or protein kinase A isozyme type I is essential in the growth inhibition of SK-N-SH cells, we overexpressed RI alpha in sense and antisense orientation. Type I protein kinase A activity was increased in the RI alpha-overexpressing cells and was decreased in the RI alpha antisense-expressing cells. However, the changes in type I protein kinase A activities did not affect cell growth. Overexpression of RII beta or C alpha increased type II protein kinase A and inhibited cell growth in both cell lines regardless of the type I protein kinase A level. These results indicate that type II protein kinase A is the main effector in the cAMP-mediated growth regulation of SK-N-SH human neuroblastoma cells.

Molecular cloning, upstream sequence and promoter studies of the human gene for the regulatory subunit RII alpha of cAMP-dependent protein kinase

The gene for the regulatory subunit RII alpha of cAMP-dependent protein kinase is highly regulated during spermatogenesis and a strong signal from a distinct short mRNA form is observed postmeiotically during spermatid elongation. This report presents the isolation and characterization of the 5'-flanking region (1.2 kb) and exon 1 of the human RII alpha gene. S1 nuclease mapping and primer extension experiments revealed the presence of a major transcriptional start site located 208 nucleotides upstream of start for translation. The 5'-flanking region of the RII alpha gene did not contain a TATA box and was highly G/C-rich. A basal promoter directing high levels of chloramphenicol acetyl transferase (CAT) activity was identified in the 5'-flanking sequence. Several potential binding sites for transcription factors were identified in this region, which may be responsible for the germ cell-specific regulation of this gene. We have previously reported that the human testis RII alpha cDNA contains a region (amino acids 45-75) with little or no homology to the corresponding rat skeletal muscle cDNA (Oyen, O., Myklebust, F., Scott, J.D., Cadd, G.G., McKnight, G.S., Hansson, V. and Jahnsen, T. (1990) Biol. Reprod. 43, 46-54). We examined whether this difference could arise due to organ-specific splice mechanisms or represented a species difference. We show that the low homology region of the human RII alpha cDNA resides entirely within exon 1, and does not originate from a tissue-specific alternate splicing of this distinct region.

Cyclic AMP-dependent protein kinase (cAK) in human B cells: co-localization of type I cAK (RI alpha 2 C2) with the antigen receptor during anti-immunoglobulin-induced B cell activation

Cyclic AMP (cAMP) inhibits antigen-stimulated B cell proliferation through activation of cAMP-dependent protein kinases (cAK). We have examined the molecular composition and cellular localization of cAK in human B cells. We find that human B cells contain substantial amounts of mRNA for RI alpha, RII alpha, C alpha and C beta, barely detectable levels of RI beta mRNA, and no detectable RII beta or C gamma mRNA. At the protein level, using Western blotting and subunit-specific antibodies against the different R subunits, we find RI alpha and RII alpha, but no RI beta or RII beta. The presence of catalytic subunits was demonstrated using a nonselective anti-C antiserum. By photoaffinity labeling of R subunits with 8-azido-[32P]cAMP, followed by immunoprecipitation with subunit-specific antibodies, we were also able to demonstrate low levels of RI beta. Immunofluorescence staining of RI alpha and RII alpha demonstrates a rather homogeneous intracellular (but extranuclear) distribution of RI alpha, whereas the RII alpha subunits of cAK are localized to distinct perinuclear structures, previously identified as centrosomes in other cell types. Upon anti-Ig-mediated capping of B cells, RI alpha subunits redistribute to the cap, co-localizing with the antigen-receptors, whereas the intracellular localization of RII alpha subunits remains unchanged.

Cloning from Leishmania major of a developmentally regulated gene, c-lpk2, for the catalytic subunit of the cAMP-dependent protein kinase

Protein kinases are important in the regulation of cellular processes including growth and differentiation. Using the polymerase chain reaction with oligonucleotide primers derived from conserved regions of cAMP-dependent protein kinases (PKAs), three different DNA fragments were amplified from leishmanial genomic DNA. One fragment was used to isolate a stage specific gene, c-lpk2, from a Leishmania major genomic library. This gene shows high homology to other eukaryotic PKAs, and the open reading frame encodes a 332 amino acid protein with a predicted molecular mass of 38.2 kDa. When aligned with other PKAs the leishmanial enzyme has a unique eight amino acid extension at the carboxy terminus. The c-lpk2 gene is present as a single copy in L. major, L. donovani and L. amazonensis. The 5'-flanking region contains a polypyrimidine rich tract upstream from the predicted ATG start codon. The gene is highly expressed in promastigotes and barely detectable in amastigotes of L. major. Temperature increase was shown to rapidly down-regulate c-lpk2 expression. Transfer of L. amazonensis promastigotes to 35 degrees C resulted in the rapid disappearance of c-lpk2 mRNA (> 70% in 1 h), while at 26 degrees C the mRNA was more stable. The strict temperature dependence of mRNA degradation rate suggests that PKA expression is regulated post-transcriptionally.

Association of the regulatory subunit of a type II cAMP-dependent protein kinase and its binding proteins with the fibrous sheath of rat sperm flagellum

Demembranated rat sperm flagellar polypeptides capable of binding the regulatory subunit (RII) of a type II cAMP-dependent protein kinase, having apparent subunit molecular masses of 120, 80 and 57 kDa were identified by an RII overlay procedure [Horowitz, J. A., Wasco, W., Leiser, M. & Orr, G. A. (1988) J. Biol. Chem. 263, 2098-2104]. In this study it is shown that all three polypeptides capable of binding RII on a solid-phase blot are tightly associated with the fibrous sheath. Purified fibrous sheath preparations were capable of binding (a) [3H]cAMP and (b) purified catalytic subunits of cAMP-dependent protein kinase forming a functional holoenzyme. The 57-kDa protein was identified as RII by photoaffinity labeling with 8-azido[32P]cAMP. This peptide was phosphorylated by the catalytic subunit of cAMP-dependent protein kinase. RII alpha was also shown to form tight, specific complexes with the fibrous sheath demonstrating the presence of functional RII alpha-binding sites. Truncated RII beta fusion proteins were used to identify the N-terminal amino acids at positions 1-50 as a primary determinant for RII-binding protein interaction. Differential extraction of adult testis with buffers containing Triton X-100, urea and sodium dodecyl sulfate revealed the presence of 80-kDa (major) and 120-kDa (minor) RII-binding proteins in particulate extracts. The 80-kDa polypeptide is only expressed at late stages of spermatogenesis, i.e. during spermiogenesis, suggesting a developmental role for RII anchoring to the sperm flagellar fibrous sheath.

Characterization of recombinant RI beta and evaluation of the presence of RI beta protein in rat brain and testicular extracts

Based upon recent reports that the mRNA from the regulatory (R) RI beta subunit of cAMP-dependent protein kinase (PKA) was expressed in testicular extracts, we determined whether testicular extracts exhibited RI beta protein. To accomplish this goal, we initially determined the fundamental labeling and ionic characteristics of recombinant RI beta. Recombinant RI beta eluted from DEAE-cellulose with a salt concentration (of 0.075 M) equivalent to its elution position from soluble mouse brain extracts with catalytic subunit-free RI alpha. As predicted by its amino acid sequence homology to RI alpha, recombinant RI beta was not phosphorylated by PKA but was labeled specifically with 8-azido-adenosine 3':5'-[32P]monophosphate (8-N3[32P]cAMP). Additionally, RI antisera reacted equally with RI alpha (47 kDa) and recombinant RI beta (53 kDa). However, recombinant RI beta exhibited an unexpectedly basic pI of 6.65-6.85. By using a pH gradient for isoelectric focussing that allowed for clear focussing of 8-N3[32P]cAMP-labeled recombinant RI beta, 8-N3[32P]cAMP-labeled RI beta was readily detected by two-dimensional gel electrophoresis in rat brain particulate extracts and exhibited a pI equivalent to that of recombinant RI beta. The 53-kDa RI beta was undetectable either by its immunoreactivity or upon photoaffinity labeling with 8-N3[32P]cAMP by one or two-dimensional gel electrophoresis in soluble or particulate extracts of testes of 14-day-old, 45-day-old, or adult rats or in epididymal sperm. However, 8-N3[32P]cAMP-labeled RI beta was detected, albeit in very small levels, by two-dimensional electrophoresis upon separation of PKAs in testes of 14-day-old rats by DEAE-cellulose chromatography but was absent in equivalent extracts from adult rat testes. These results demonstrate that the unexpectedly basic pI of RI beta allows for its clear separation by two-dimensional electrophoresis from the RII proteins and therefore allows for its unambiguous identification. Further studies, however, are required to resolve the basis for the apparent disparity in testis RI beta mRNA and protein.

Expression of protein kinase A and protein kinase C during ongoing human cytomegalovirus infection

During an HCMV infection, transcription of viral and cellular genes are mutually regulated. Several cellular proteins have been implicated in the regulation of the HCMV major immediate early promoter (MIEP) which have been shown to respond to cAMP as well as activation of protein kinase C (PKC). We have examined the effect of an ongoing HCMV infection at the mRNA level for the catalytic and regulatory subunits of protein kinase A (PKA) and alpha and beta isoforms of PKC. There was a moderate elevation for PKA C alpha and RI alpha at immediate early times (0.5-2 h) after HCMV infection. Later in the infection cycle (24-72 h), mRNA level for PKA regulatory subunit RI alpha and PKC alpha were decreased compared with control cells. Messenger RNA levels for the PKA RII alpha and RII beta as well as PKC beta were not affected by HCMV infection. During the infection cycle the PKA subunits and PKC isoforms appeared to be independently regulated. It was also evident that the basal mRNA levels of PKA subunits and the PKC isoforms were sufficient for the PKA and PKC activity required during an HCMV infection in permissive fibroblast cells.

Characterization of in-vitro-translated human regulatory and catalytic subunits of cAMP-dependent protein kinases

Full-length human cDNAs for all the different regulatory (R) and catalytic (C) subunits of cAMP-dependent protein kinases (PKA) were transcribed and translated in a cell-free in vitro system. The resulting proteins were characterized with respect to molecular size, isoelectric focusing, immunoreactivity, cAMP binding, and to what extent the RII protein subunits revealed mobility shifts upon phosphorylation by catalytic subunit of PKA. We were able to express cDNAs for all the human R (RI alpha, RI beta, RII alpha and RII beta) and C (C alpha, C beta and C gamma) subunits in a wheat-germ extract. [35S]Methionine-labelled in-vitro-translated products were analyzed by SDS/PAGE and revealed distinct protein bands with apparent molecular masses of 49 (RI alpha), 54-55 (RI beta), 51 (RII alpha) and 53 kDa (RII beta) for the R subunits. In vitro transcription/translation of the cDNAs for the C subunits of PKA gave proteins with molecular masses of approximately 40 kDa for all the different C subunits. Phosphorylation of RII alpha and RII beta by the C subunit of PKA, revealed a distinct mobility shift of the RII alpha subunit on one-dimensional SDS/PAGE (51-54 kDa), but not of RII beta (53 kDa). Further characterization of the R subunits by two-dimensional SDS/PAGE revealed that RI alpha was more acidic than RI beta, with pIs of 6.1-6.0 and 6.4-6.2, respectively. Furthermore, the RII alpha protein was more basic than RII beta, with pIs of approximately 5.4-5.3 and 5.3-5.1, respectively. All the in-vitro-translated R subunits could be photoaffinity labelled by the cAMP-analog 8-azido-[32P]cAMP and were also detected by immunoprecipitation with subunit-specific antibodies.

Increase in [3H]cAMP binding sites and decrease in Gi alpha and Go alpha immunoreactivities in left temporal cortices from patients with schizophrenia

To search for possible alterations in second messenger systems in the temporal cortex (Brodmann's area 22) of patients with schizophrenia, we measured the binding activities of [3H]adenosine 3',5'-cyclic monophosphate ([3H]cAMP) and [3H]4 beta-phorbol 12,13-dibutyrate ([3H]PDBu) which can label the regulatory subunit of cAMP-dependent protein kinase (protein kinase A) and the regulatory domain of Ca2+/phospholipid-dependent protein kinase (protein kinase C), respectively. We also immunoquantified the variable subunits of guanine nucleotide binding proteins (G-proteins), using specific polyclonal antisera against Gs alpha, Gi alpha and Go alpha. Brains were obtained at autopsy on 10 patients with schizophrenia and 10 age-matched control subjects. Representative Scatchard plots for specific [3H]cAMP bindings to the soluble fraction consisted of a single component with high affinity (Kd = 2.36 nM, Bmax = 737 fmol/mg protein). Among the tested adenyl and guanyl nucleotides, or neuroleptics, cAMP alone potently inhibited the binding (Ki = 4.95 nM). The binding sites for [3H]cAMP were discretely localized, and were in the order of: cerebral cortex = hypothalamus = amygdala > hippocampus = neostriatum = thalamus = nucleus accumbens > globus pallidus = cerebellum. Specific [3H]cAMP bindings to the soluble fractions were about 30% greater in the left temporal cortices of schizophrenic patients, as compared to findings in the right side of the patients and the left side of the control subjects, no control brain showed this asymmetry. The specific [3H]PDBu binding in schizophrenic and control groups did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Mapping of the regulatory subunits RI beta and RII beta of cAMP-dependent protein kinase genes on human chromosome 7

The genes encoding the regulatory subunits RI beta (locus PRKAR1B) and RII beta (locus PRKAR2B) of human cAMP-dependent protein kinase have been mapped in the basic CEPH (Centre d'Etude du Polymorphisme Humain) family panel of 40 families to chromosome 7p and 7q, respectively, using the enzymes HindIII and BanII recognizing the corresponding restriction fragment length polymorphisms (RFLPs). Previous data from the CEPH database and our present RFLP data were used to construct a six-point local framework map including PRKAR1B and a seven-point framework map including PRKAR2B. The analysis placed PRKAR1B as the most distal of the hitherto mapped 7p marker loci and resulted in an unequivocal order of pter-PRKAR1B-D7S21-D7S108-D7S17-D7S149- D7S62-cen, with a significantly higher rate of male than female recombination between PRKAR1B and D7S21. The 7q regulatory gene locus, PRKAR2B, could also be placed in an unambigous order with regard to the existing CEPH database 7q marker loci, the resulting order being cen-D7S371-(COL1A2,D7S79)-PRKAR2B-MET-D7S87++ +-TCRB-qter. Furthermore, in situ hybridization to metaphase chromosomes physically mapped PRKAR2B to band q22 on chromosome 7.

cAMP-dependent protein kinases in the rat testis: regulatory and catalytic subunit associations

Based upon recent reports that the rat testis exhibits mRNAs for cAMP-dependent protein kinase (A-kinase) regulatory (R) subunits RI alpha, RI beta, RII alpha, and RII beta, this study was designed to identify R proteins present in extracts of germ cell-rich testis from adult and Sertoli cell-enriched, germ cell-poor testis from 14-15-day-old rats. Following separation by DEAE-cellulose, R subunits were identified by Mr: (a) upon labeling with 8-N3[32P]cAMP and 32P in an RII phosphorylation reaction and; (b) by Western blot analysis using R-specific antibodies on one- and two-dimensional gel electrophoresis. Elution of R subunits as catalytic (C) subunit-free dimers or in association with C subunits to form holoenzyme was determined by their sedimentation characteristics on sucrose gradient centrifugation in conjunction with their cAMP-stimulated activation characteristics on Eadie-Scatchard analysis. Soluble extracts of testes, from both adult and 14-15 day-old rats, showed the presence of a prominent type I holoenzyme containing RI alpha subunits (47 kDa, peak 1), a minor type II holoenzyme, containing RII beta subunits (52 kDa, peak 2), and a second, more abundant, type II holoenzyme peak containing predominantly RII alpha and, to a lesser extent RII beta subunits (peak 3). The 53 kDa RI beta protein predicted by mRNA studies was only tentatively identified by Western blot analysis. Testes extracts of 14-15-day-old, but not adult, rats exhibited high levels of C subunit-free RI alpha, a result not predicted by mRNA studies. This latter result may be attributable to direct RI alpha regulation or to indirect RII beta regulation at a time during testis development prior to germ cell maturation.

Molecular cloning and characterization of the promoter region of the mouse regulatory subunit RII beta of type II cAMP-dependent protein kinase

The promoter and exon 1 of the regulatory subunit (RII beta) of type II cAMP-dependent protein kinase were isolated from a mouse genomic library. The 5'-flanking DNA lacked TATA and CAAT sites but contained GC rich regions typically found in constitutively expressed house keeping genes. Fusion gene constructs, containing RII beta 5'-flanking sequences and the bacterial CAT structural gene, were transfected into NB2a neuroblastoma cells and CHO cells. The NB2a cells expressed high levels of CAT activity. CHO cells expressed CAT activity at 5% of the level seen in the NB2a cells. Transfection of deletion constructs into both cell lines was used to define the core promoter and enhancer elements. The core promoter was situated between bp -291/-121. An enhancer element was located between bp -1426/-1018.