The neural type II regulatory subunit of cAMP-dependent protein kinase is present and regulated by hormones in the rat ovary

A-kinase anchoring protein 8L interacts with mTORC1 and promotes cell growth

mTOR complex 1 (mTORC1) senses nutrients to mediate anabolic processes within the cell. Exactly how mTORC1 promotes cell growth remains unclear. Here, we identified a novel mTORC1-interacting protein called protein kinase A anchoring protein 8L (AKAP8L). Using biochemical assays, we found that the N-terminal region of AKAP8L binds to mTORC1 in the cytoplasm. Importantly, loss of AKAP8L decreased mTORC1-mediated processes such as translation, cell growth, and cell proliferation. AKAPs anchor protein kinase A (PKA) through PKA regulatory subunits, and we show that AKAP8L can anchor PKA through regulatory subunit Iα. Reintroducing full-length AKAP8L into cells restored mTORC1-regulated processes, whereas reintroduction of AKAP8L missing the N-terminal region that confers the interaction with mTORC1 did not. Our results suggest a multifaceted role for AKAPs in the cell. We conclude that mTORC1 appears to regulate cell growth, perhaps in part through AKAP8L.

Isoform-specific subcellular localization and function of protein kinase A identified by mosaic imaging of mouse brain

Protein kinase A (PKA) plays critical roles in neuronal function that are mediated by different regulatory (R) subunits. Deficiency in either the RIβ or the RIIβ subunit results in distinct neuronal phenotypes. Although RIβ contributes to synaptic plasticity, it is the least studied isoform. Using isoform-specific antibodies, we generated high-resolution large-scale immunohistochemical mosaic images of mouse brain that provided global views of several brain regions, including the hippocampus and cerebellum. The isoforms concentrate in discrete brain regions, and we were able to zoom-in to show distinct patterns of subcellular localization. RIβ is enriched in dendrites and co-localizes with MAP2, whereas RIIβ is concentrated in axons. Using correlated light and electron microscopy, we confirmed the mitochondrial and nuclear localization of RIβ in cultured neurons. To show the functional significance of nuclear localization, we demonstrated that downregulation of RIβ, but not of RIIβ, decreased CREB phosphorylation. Our study reveals how PKA isoform specificity is defined by precise localization.

DOI:http://dx.doi.org/10.7554/eLife.17681.001

Dissecting interdomain communication within cAPK regulatory subunit type IIbeta using enhanced amide hydrogen/deuterium exchange mass spectrometry (DXMS)

cAMP-dependent protein kinase (cAPK) is a heterotetramer containing a regulatory (R) subunit dimer bound to two catalytic (C) subunits and is involved in numerous cell signaling pathways. The C-subunit is activated allosterically when two cAMP molecules bind sequentially to the cAMP-binding domains, designated A and B (cAB-A and cAB-B, respectively). Each cAMP-binding domain contains a conserved Arg residue that is critical for high-affinity cAMP binding. Replacement of this Arg with Lys affects cAMP affinity, the structural integrity of the cAMP-binding domains, and cAPK activation. To better understand the local and long-range effects that the Arg-to-Lys mutation has on the dynamic properties of the R-subunit, the amide hydrogen/deuterium exchange in the RIIbeta subunit was probed by electrospray mass spectrometry. Mutant proteins containing the Arg-to-Lys substitution in either cAMP-binding domain were deuterated for various times and then, prior to mass spectrometry analysis, subjected to pepsin digestion to localize the deuterium incorporation. Mutation of this Arg in cAB-A (Arg230) causes an increase in amide hydrogen exchange throughout the mutated domain that is beyond the modest and localized effects of cAMP removal and is indicative of the importance of this Arg in domain organization. Mutation of Arg359 (cAB-B) leads to increased exchange in the adjacent cAB-A domain, particularly in the cAB-A domain C-helix that lies on top of the cAB-B domain and is believed to be functionally linked to the cAB-B domain. This interdomain communication appears to be a unidirectional pathway, as mutation of Arg230 in cAB-A does not effect dynamics of the cAB-B domain.

Differential localization of protein kinase A type II isozymes in the Golgi-centrosomal area

Selectivity in the action of cAMP may be mediated by compartmentalized pools of cyclic AMP-dependent protein kinase (PKA). PKA type II is directed to different subcellular loci by interaction of the type II regulatory subunits (RIIalpha, RIIbeta) with A-kinase anchoring proteins. In order to separately investigate the subcellular localization of PKA type II isozymes, monospecific antibodies to human RIIalpha and RIIbeta subunits of PKA were developed. We demonstrate that centrosomes bind both RIIalpha and RIIbeta. Centrosomes were the preferred intracellular anchoring site for RIIbeta. However, centrosomal localization of RIIbeta was observed only in some highly differentiated cells such as keratinocytes, granulosa cells, and macrophages and in all neoplastic cell lines examined. Centrosomal localization of RIIbeta was not observed in normal undifferentiated cells such as fibroblasts, myoblasts, and T and B cells. In contrast, RIIalpha was abundant in the Golgi area and in the trans-Golgi network (TGN). Furthermore, although RIIalpha appeared to colocalize with microtubules in the Golgi/TGN, extractions with nonionic detergent demonstrated that RIIalpha was mainly membrane-associated. In addition, alterations of microtubule dynamics with Nocodazole or Taxol affected the distribution of the detergent-extractable pool of RIIalpha, indicating that RIIalpha may localize with microtubule-associated vesicles. Thus, RIIalpha and RIIbeta clearly localize differently in the Golgi-centrosomal region. This indicates specific roles for PKA isozymes containing either RIIalpha or RIIbeta.

Growth factors and phorbol-12-myristate-13-acetate modulate the follicle-stimulating hormone- and cyclic adenosine-3',5'-monophosphate-dependent regulation of 17beta-hydroxysteroid dehydrogenase type 1 expression in rat granulosa cells

In the present study primary cultures of rat granulosa cells obtained from diethylstilbestrol (DES)-primed immature rats were used to study the regulation of 17beta-hydroxysteroid dehydrogenase (17HSD) activity and type 1 expression via protein kinase A (PKA)- and C (PKC)-dependent pathways, and by several autocrine and/or paracrine growth factors. Follicle-stimulating hormone (FSH), 8-bromo-cyclic adenosine-3',5'-monophosphate (8-Br-cAMP) and transforming growth factor beta1 (TGFbeta1) strongly enhanced 17HSD activity and type 1 expression. The stimulatory effects of FSH and 8-Br-cAMP were further potentiated by TGFbeta1. In contrast, neither phorbol-12-myristate-13-acetate (PMA), epidermal growth factor (EGF), transforming growth factor alpha (TGFalpha) nor fibroblast growth factor (bFGF) affected 17HSD activity or type 1 expression when given alone. However, they effectively neutralized the stimulatory effects of 8-Br-cAMP and FSH. The present data suggest that, in rat granulosa cells 17HSD type 1 expression is primarily induced by FSH acting via PKA-dependent pathway and the extent of the induction is modulated by PKC-dependent inhibition and autocrine/paracrine growth factors present in the ovary.

Cyclic AMP-dependent protein kinase in ovarian follicle cells of starfish Asterina pectinifera

Adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA) in ovarian follicle cells of the starfish Asterina pectinifera was studied. Protein kinase activity in follicle cell homogenate was activated by cAMP in a dose-dependent manner, and Ka was obtained with 10(-7) M cAMP. The PKA activity required Mg2+ at concentrations between 2 and 10 mM. On Sephacryl S-300 column chromatography of partially purified PKA, Mr of the holoenzyme was estimated to be about 180,000. [2,3-3H]cAMP binding activity also suggested a regulatory subunit of Mr about 50,000. DE-52 column chromatography of the cell extract resolved the enzyme activity into two peaks, which eluted between 0.05 and 0.1 M NaCl (type I), and between 0.15 and 0.25 M NaCl (type II). The type I enzyme was the predominant form of PKA in starfish follicle cells. In a cell-free system, a 70 kDa protein was phosphorylated during incubation with [gamma-32P]ATP in the presence of cAMP. These results suggest that PKA stimulates the phosphorylation of a 70 kDa protein following an increase in the level of cAMP.

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.

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.

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.

The cAMP-dependent signalling cascade in the two luteal cell types of the pregnant rat corpus luteum

Corpora lutea of rats, like those of many other species, contain two sub-populations of luteal cells. In this report we sought to determine whether the luteinizing hormone (LH)- and beta-adrenergic cAMP signal transduction pathways known to be present in rat corpora lutea were segregated into separate luteal cell types. Results showed that large rat luteal cells, obtained on day 3 of pregnancy, exhibited elevated LH- and most notably epinephrine-stimulated adenylyl cyclase activities but equivalent cAMP-dependent catalytic protein kinase and total regulatory subunit cAMP binding activities compared to small luteal cells. Progesterone production by the large cell was greater than that by the small cell but both cells were equally sensitive to stimulation of progesterone by LH. However, neither the large nor the small rat luteal cell produced significant progesterone in response to epinephrine despite a marked epinephrine-stimulated adenylyl cyclase in both cell populations. The LH-stimulated progesterone synthetic response of the two sub-populations of rat luteal cells is more similar to that of the developing monkey corpus luteum and contrasts sharply with that of ruminants.

The regulatory subunit of the type II cAMP-dependent protein kinase in rabbit ovaries is the RII beta isoform

Based on RII autophosphorylation, photoaffinity labeling with 8-N3[32P]cAMP, and Western blot analysis we have identified the RII isoform found in rabbit corpora lutea as RII beta. The RII beta subunit found in rabbit corpora lutea differs from the RII beta found in rat follicles and corpora lutea in that it migrates at Mr 52,500 on SDS-PAGE and shifts to Mr 53,000 when phosphorylated.

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.

Identification of a 50-kDa Ca-, cAMP-, and cGMP-dependent epithelial phosphoprotein as a cAMP regulatory protein

Multiple second messengers, presumably acting via protein phosphorylation mechanisms, regulate flounder intestinal ion transport. We recently reported [C. Toskulkao, N. T. Nash, K. Leach, and M. C. Rao. Am. J. Physiol. 258 (Cell Physiol. 27): C879-C888, 1990] that this tissue possesses adenosine 3',5'-cyclic monophosphate (cAMP)- and guanosine 3',5'-cyclic monophosphate (cGMP)-specific protein kinases, types II and III Ca-calmodulin kinases, and very low levels of protein kinase C. These results correlate with ion transport studies in which cGMP and Ca were shown to inhibit salt absorption, cAMP to increase anion permeability, and phorbol esters to have no effect. In the present study we characterized in detail a 50-kDa protein the phosphorylation of which is regulated by more than one second messenger. The 50-kDa (pI 5.2) phosphoprotein is present in both the cytosol (50 kDa-C) and particulate (50 kDa-P) fractions and appears to be regulated by Ca, cAMP, and cGMP. Although the pI and Mr of the regulated proteins are identical, there are differences in the regulation of 50 kDa-P and 50 kDa-C. The phosphorylation of 50 kDa-P is high in the basal state, and Ca and cGMP enhance this. cAMP has a biphasic effect, increasing it at low and decreasing it at high protein concentrations. The isoquinoline derivatives H-8 [50% effective dose (ED50) approximately 2.3 microM] and H-7 (ED50 approximately 45 microM) inhibit basal 50 kDa-P phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Second messenger-specific protein kinases in a salt-absorbing intestinal epithelium

Calcium, adenosine 3',5'-cyclic monophosphate (cAMP), and guanosine 3',5'-cyclic monophosphate (cGMP) can regulate the same or different ion transport processes within an epithelium, presumably via independent protein phosphorylation mechanisms. Because there have been few detailed studies characterizing these processes in epithelia, we examined the distribution of Ca-, cAMP-, and cGMP-specific protein kinases and substrates in vitro in a homogenous salt-absorbing epithelium, the winter flounder intestine. In this tissue cGMP and Ca inhibit Na-K-2Cl cotransport, cAMP increases anion permeability, and phorbol esters do not affect ion transport. The Ca-specific kinases are calmodulin (CaM) dependent. The tissue possesses type III Ca-CaM protein kinase and its specific substrate elongation factor 2 and type II but not type I Ca-CaM kinase. Addition of phosphatidylserine (PS) and Ca to crude or DEAE-cellulose-purified cytosol neither increased the phosphorylation of exogenous histone H1 substrate nor that of any endogenous substrates. Although these suggest the absence of Ca-phospholipid-dependent kinase (PKC), the cytosol has a 78-kDa protein recognizable by a highly specific polyclonal sheep antibody to rat brain PKC. Both the particulate and cytosolic fractions possess cAMP-specific binding proteins and cAMP-specific phosphoprotein substrates. The particulate fraction cAMP-binding proteins are of molecular mass 50 kDa (pI 5.2) and 48 kDa with multiple isoforms (pI 5.6-6.2); these proteins generate different peptide maps. The cytosol chiefly contains a 50-kDa (pI 5.2) cAMP binding protein that is similar to the particulate 50-kDa protein on peptide mapping. The flounder cAMP binding proteins have the same pI but lower molecular mass and different peptide profiles than the rat brain RII (54/52 kDa) and RI (50 kDa) cAMP regulatory proteins. The cGMP-specific protein kinase was less prominent, very low levels of cGMP-specific binding proteins being detected either by equilibrium binding or by photoaffinity labeling. A prominent kinase substrate in homogenates is a 50-kDa protein, the phosphorylation of which is increased by Ca and cGMP but decreased by cAMP. When intact tissue was prelabeled with 32Pi and then exposed to cGMP, the phosphorylation of a number of substrates including that of a 50-kDa protein was increased. In summary, the flounder intestine possesses the necessary protein phosphorylation mechanisms to account for the regulation of its ion transport processes by second messengers.

Localization and characterization of the binding site for the regulatory subunit of type II cAMP-dependent protein kinase on MAP2

Microtubule-associated protein 2 (MAP2) binds, and is a substrate for, type II cAMP-dependent protein kinase. The structural domain in MAP2 that binds the regulatory subunit (RII) of protein kinase II was identified by expressing fragments of a human MAP2 cDNA in E. coli using the pATH11 vector. Fusion proteins were resolved by SDS-PAGE and transferred to nitrocellulose. The filters were probed with purified bovine heart or brain RII, anti-RII monoclonal antibodies, and 125I-labeled protein A. Binding of RII was localized to a 31 amino acid sequence near the N-terminus of the MAP2 molecule. Fusion proteins containing this fragment bound both heart and brain RIIs in a concentration-dependent manner, but bound heart RII with a higher apparent affinity than brain RII. The amino acid sequence of this fragment (DRETAEEVSARIVQVVTAEAVAVLKGEQEKE) is totally conserved between human and mouse MAP2, suggesting an important role for the RII binding site of MAP2 in neuronal function.

Biochemical and immunological characterization of the flagellar-associated regulatory subunit of a type II cyclic adenosine 5'-monophosphate-dependent protein kinase

We have shown previously that the regulatory subunit (RII) of a type II cyclic AMP (cAMP)-dependent protein kinase is tightly associated with mammalian sperm flagella (J. A. Horowitz et al. (1984) J. Biol. Chem. 259, 832-838; J. A. Horowitz et al. (1988) J. Biol. Chem. 263, 2098-2104). In the present study the flagellar RII was compared to other well-characterized RIIs using biochemical and immunological methods. Flagellar polypeptides were screened by immunoblot analysis with monoclonal antibodies directed against the RII alpha and RII beta isoforms. An RII beta monoclonal antibody failed to cross-react with any flagellar polypeptide. In contrast, mAB 622, an RII alpha/RII beta monoclonal antibody, cross-reacted with a 57,000 Da polypeptide. However, another RII alpha/RII beta monoclonal antibody interacted weakly with the flagellar RII, suggesting that the epitope for this antibody is modified in flagellar RII. Partial peptide mapping of 8-azido-[32P]cAMP-labeled RIIs revealed that although heart and testis generated similar fragmentation patterns, there were differences in the maps from flagellar RII. Two-dimensional sodium dodecyl sulfate-gel electrophoresis of 8-azido-[32P]cAMP-labeled RII from rat flagella and bovine heart showed that the former possessed a considerably more acidic isoelectric point. Partial proteolysis of the flagellar RII by either endogenous or exogenous proteases resulted in the cleavage of RII to a 40,000 Mr fragment. Complete release of this fragment from the flagellum was achieved if proteolysis was performed in the presence of thiol reducing agents. In their absence, approximately 50% of the fragment remained bound to the flagellum. The soluble proteolytic fragment was shown to be monomeric by native high-resolution gel-permeation chromatography and contained a functional cAMP-binding site(s).

Rectum has abnormal ion transport but normal cAMP-binding proteins in cystic fibrosis

The luminal membranes of involved tissues in cystic fibrosis (CF) are relatively impermeable to Cl and the regulation of Cl transport by adenosine 3',5'-cyclic monophosphate (cAMP)-mediated hormones is abnormal. We investigated the human rectum as a putative model for CF. We compared in vivo transrectal potential difference (PD) in CF and in normal subjects in response to sequential perfusions with various test solutions. The base-line PD was different in normal (-35.5 +/- 4.0 mV; lumen negative; mean +/- SE; n = 9) and CF subjects (-23.4 +/- 3.1 mV; n = 6; P less than 0.025) and was eliminated by amiloride (10(-4) M) perfusion in both groups by 3 min. However, in response to a Cl-free solution with amiloride, all six CF subjects exhibit less of a change in PD (PD, -2.2 +/- 1.2 mV vs. -11.7 +/- 1.5 mV in 6 controls; P less than 0.01). Furthermore, normal subjects (n = 7) respond to a 5 mM theophylline + amiloride perfusion with an increase in lumen-negative PD, whereas, CF subjects (n = 6) show no increase in lumen-negative PD. Rectal biopsy specimens from four normal and four CF subjects exhibit similar (2- to 3-fold) increases in theophylline-induced cAMP content and have similar cAMP-binding proteins (CF, n = 3; control, n = 3). We conclude that the rectum is an involved epithelium in CF in which the aberration may lie at a point beyond the binding of cAMP to its protein kinase.

The cAMP cascade in the nervous system: molecular sites of action and possible relevance to neuronal plasticity

Many intercellular messages regulate the activity of their target cells by altering the intracellular level of cAMP and, as a consequence, the phosphorylation state of proteins which serve as substrates for cAMP-dependent protein kinase. Such regulation plays a crucial role in neuronal development, neuronal function, and neuronal plasticity (e.g., elementary learning mechanisms). Ample information has been accumulated in recent years on the enzymes that regulate the level of cAMP or respond to it, on the regulation of cAMP synthesis by neurohormones, neurotransmitters, ions, and toxins, on neuronal-specific substrate proteins that are phosphorylated by the cAMP-dependent kinase, and on the interaction of the cAMP-cascade with other second-messenger systems within neurons. Such data, obtained by a combination of molecular-biological, biochemical, and cellular approaches, shed light on the detailed mechanisms by which modulation of a ubiquitous molecular cascade leads to a great variety of short-term as well as long-term specific neuronal responses and alterations.

Expression cloning of a cDNA encoding the type II regulatory subunit of the cAMP-dependent protein kinase

We report here the isolation and sequence of a cDNA for the type II regulatory subunit of the cAMP-dependent protein kinase (cAMP-PK) from a lambda gt-11 cDNA library derived from a porcine epithelial cell line (LLC-PK1). The cDNA was detected by immunological screening using an affinity purified polyclonal antibody for bovine RII. DNA sequence analysis of the 467 bp EcoRI insert confirmed the identity of the clone, because the deduced amino acid sequence corresponded to the published sequence for the bovine RII protein. Northern analysis of total RNA from the LLC-PK1 cells indicated a single mRNA species of about 6.0 kb, probably derived from a single copy gene.