Isolation and characterization of cDNAs corresponding to two human calcium, calmodulin-regulated, 3',5'-cyclic nucleotide phosphodiesterases

Phosphodiesterase 1 Upregulation in Pulmonary Arterial Hypertension

Background— Pulmonary arterial hypertension (PAH) is a life-threatening disease, characterized by vascular smooth muscle cell hyperproliferation. The calcium/calmodulin-dependent phosphodiesterase 1 (PDE1) may play a major role in vascular smooth muscle cell proliferation.

Methods and Results— We investigated the expression of PDE1 in explanted lungs from idiopathic PAH patients and animal models of PAH and undertook therapeutic intervention studies in the animal models. Strong upregulation of PDE1C in pulmonary arterial vessels in the idiopathic PAH lungs compared with healthy donor lungs was noted on the mRNA level by laser-assisted vessel microdissection and on the protein level by immunohistochemistry. In chronically hypoxic mouse lungs and lungs from monocrotaline-injected rats, PDE1A upregulation was detected in the structurally remodeled arterial muscular layer. Long-term infusion of the PDE1 inhibitor 8-methoxymethyl 3-isobutyl-1-methylxanthine in hypoxic mice and monocrotaline-injected rats with fully established pulmonary hypertension reversed the pulmonary artery pressure elevation, structural remodeling of the lung vasculature (nonmuscularized versus partially muscularized versus fully muscularized small pulmonary arteries), and right heart hypertrophy.

Conclusions— Strong upregulation of the PDE1 family in pulmonary artery smooth muscle cells is noted in human idiopathic PAH lungs and lungs from animal models of PAH. Inhibition of PDE1 reverses structural lung vascular remodeling and right heart hypertrophy in 2 animal models. The PDE1 family may thus offer a new target for therapeutic intervention in pulmonary hypertension.

Low-Dose Phosphodiesterase Inhibition Improves Responsiveness to Inhaled Nitric Oxide in Isolated Lungs From Endotoxemic Rats

BACKGROUND

Inhalation of nitric oxide (NO) and inhibition of phosphodiesterase type 5 (PDE5) selectively dilate the pulmonary circulation in patients with acute lung injury (ALI) associated with pulmonary hypertension. PDE5 inhibitors administered at doses that decrease pulmonary artery pressures have been shown to worsen arterial oxygenation. We investigated the efficacy of doses of PDE5 inhibitors that do not reduce pulmonary artery pressure alone (subthreshold doses) to improve the response to inhaled NO in an animal model of ALI.

MATERIALS AND METHODS

Adult Sprague-Dawley rats were pre-treated with 0.5 mg/kg Escherichia coli 0111:B4 endotoxin and 16 to 18 h later, their lungs were isolated perfused and ventilated. The thromboxane mimetic U46619 was used to induce pulmonary hypertension. After the determination of subthreshold doses of two different PDE5 inhibitors, either 50 microg zaprinast or 10 ng sildenafil was added to the perfusate and the decrease of pulmonary artery pressure measured in the presence and absence of inhaled NO.

RESULTS

In the presence of 4 or 10 ppm NO, zaprinast (-1.6 +/- 0.4 and -2.9 +/- 0.6 mmHg, respectively) and sildenafil (-1.9 +/- 0.4 and -2.4 + 0.3 mmHg, respectively) improved responsiveness to inhaled NO compared to lungs from rats treated with LPS only (0.7 +/- 0.1 and -1.0 +/- 0.1 mmHg, respectively; P<0.05). Neither zaprinast nor sildenafil prolonged the pulmonary vasodilatory response to inhaled NO.

CONCLUSIONS

Subthreshold doses of PDE5 inhibitors improved responsiveness to inhaled NO. Combining inhaled NO with subthreshold doses of PDE5 inhibitors may offer a therapeutic strategy with minimal side-effects in ALI associated with pulmonary hypertension.

Overview of PDEs and their regulation

Contraction and relaxation of vascular smooth muscle and cardiac myocytes are key physiological events in the cardiovascular system. These events are regulated by second messengers, cAMP and cGMP, in response to extracellular stimulants. The strength of signal transduction is controlled by intracellular cyclic nucleotide concentrations, which are determined by a balance in production and degradation of cAMP and cGMP. Degradation of cyclic nucleotides is catalyzed by 3',5'-cyclic nucleotide phosphodiesterases (PDEs), and therefore regulation of PDEs hydrolytic activity is important for modulation of cellular functions. Mammalian PDEs are composed of 21 genes and are categorized into 11 families based on sequence homology, enzymatic properties, and sensitivity to inhibitors. PDE families contain many splice variants that mostly are unique in tissue-expression patterns, gene regulation, enzymatic regulation by phosphorylation and regulatory proteins, subcellular localization, and interaction with association proteins. Each unique variant is closely related to the regulation of a specific cellular signaling. Thus, multiple PDEs function as a particular modulator of each cardiovascular function and regulate physiological homeostasis.

Transgenic Mouse Proteomics Identifies New 14-3-3-associated Proteins Involved in Cytoskeletal Rearrangements and Cell Signaling

Identification of protein-protein interactions is crucial for unraveling cellular processes and biochemical mechanisms of signal transduction. Here we describe, for the first time, the application of the tandem affinity purification (TAP) and LC-MS method to the characterization of protein complexes from transgenic mice. The TAP strategy developed in transgenic mice allows the emplacement of complexes in their physiological environment in contact with proteins that might only be specifically expressed in certain tissues while simultaneously ensuring the right stoichiometry of the TAP protein versus their binding partners and represents a novelty in proteomics approaches used so far. Mouse lines expressing TAP-tagged 14-3-3zeta protein were generated, and protein interactions were determined. 14-3-3 proteins are general regulators of cell signaling and represent up to 1% of the total brain protein. This study allowed the identification of almost 40 novel 14-3-3zeta-binding proteins. Biochemical and functional characterization of some of these interactions revealed new mechanisms of action of 14-3-3zeta in several signaling pathways, such as glutamate receptor signaling via binding to homer homolog 3 (Homer 3) and in cytoskeletal rearrangements and spine morphogenesis by binding and regulating the activity of the signaling complex formed by G protein-coupled receptor kinase-interactor 1 (GIT1) and p21-activated kinase-interacting exchange factor beta (betaPIX).

Cyclic Nucleotide Phosphodiesterases: Molecular Regulation to Clinical Use

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that regulate the cellular levels of the second messengers, cAMP and cGMP, by controlling their rates of degradation. There are 11 different PDE families, with each family typically having several different isoforms and splice variants. These unique PDEs differ in their three-dimensional structure, kinetic properties, modes of regulation, intracellular localization, cellular expression, and inhibitor sensitivities. Current data suggest that individual isozymes modulate distinct regulatory pathways in the cell. These properties therefore offer the opportunity for selectively targeting specific PDEs for treatment of specific disease states. The feasibility of these enzymes as drug targets is exemplified by the commercial and clinical successes of the erectile dysfunction drugs, sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). PDE inhibitors are also currently available or in development for treatment of a variety of other pathological conditions. In this review the basic biochemical properties, cellular regulation, expression patterns, and physiological functions of the different PDE isoforms will be discussed. How these properties relate to the current and future development of PDE inhibitors as pharmacological agents is especially considered. PDEs hold great promise as drug targets and recent research advances make this an exciting time for the field of PDE research.

The role of phosphodiesterase isoforms 2, 5, and 9 in the regulation of NO-dependent and NO-independent cGMP production in the rat cervical spinal cord

NO-responsive, cGMP-producing structures are abundantly present in the cervical spinal cord. NO-mediated cGMP synthesis has been implicated in nociceptive signaling and it has been demonstrated that cGMP has a role establishing synaptic connections in the spinal cord during development. As cGMP levels are controlled by the activity of soluble guanylyl cyclase (synthesis) and the phosphodiesterase (PDE) activity (breakdown), we studied the influence of PDE activity on NO-stimulated cGMP levels in the rat cervical spinal cord. cGMP-immunoreactivity (cGMP-IR) was localized in sections prepared from slices incubated in vitro. A number of reported PDE isoform-selective PDE inhibitors was studied in combination with diethylamineNONOate (DEANO) as a NO-donor including isobutyl-methylxanthine (IBMX) as a non-selective PDE inhibitor. We studied 8-methoxy-IBMX as a selective PDE1 inhibitor, erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and BAY 60-7550 as selective PDE2 inhibitors, sildenafil as a selective PDE5 inhibitor, dipyridamole as a mixed type PDE5 and PDE10 inhibitor, rolipram as a PDE4 inhibitor, and SCH 81566 as a selective PDE9 inhibitor. cGMP-IR structures (nerve fibers, axons, and terminals) were characterized using the following neurochemical markers: vesicular transporter molecules for acetylcholine, GABA, and glutamate (type 1 and type 2), parvalbumin, glutamate transporter molecule EAAT3, synaptophysin, substance P, calcitonin gene-related peptide, and isolectin B4. Most intense cGMP-IR was observed in the dorsal lamina. Ventral motor neurons were devoid of cGMP-IR. cGMP-IR was observed in GABAergic, and glutamatergic terminals in all gray matter laminae. cGMP-IR was abundantly colocalized with anti-vesicular glutamate transporter 2 (vGLUT2), however not with the anti-vesicular glutamate transporter 1 (vGLUT1), suggesting a functional difference between structures expressing vGLUT1 or vGLUT2. cGMP-IR did not colocalize with substance P- or calcitonin-gene related peptide-IR structures, however did partially colocalize with isolectin B4 in the dorsal horn. cGMP-IR in cholinergic structures was observed in dorsal root fibers entering the spinal cord, occasionally in laminae 1-3, in laminae 8 and 9 in isolated boutons and in the C-type terminals, and in small cells and varicosities in lamina 10. This latter observation suggests that the proprioceptive interneurons arising in lamina 10 are also NO-responsive. No region-specific nor a constant co-expression of cGMP-IR with various neuronal markers was observed after incubation of the slices with one of the selected PDE inhibitors. Expression of the mRNA of PDE2, 5, and 9 was observed in all lamina. The ventral motor neurons and the ependymal cells lining the central canal expressed all three PDE isoforms. Incubation of the slices in the presence of IBMX, DEANO in combination with BAY 41-2272, a NO-independent activator of soluble guanylyl cyclase, provided evidence for endogenous NO synthesis in the slice preparations and enhanced cGMP-IR in all lamina. Under these conditions cGMP-IR colocalized with substance P in a subpopulation of substance P-IR fibers. It is concluded that NO functions as a retrograde neurotransmitter in the spinal cord but that also postsynaptic structures are NO-responsive by producing cGMP. cGMP-IR in a subpopulation of isolectin B4 positive fibers and boutons is indicative for a role of NO-cGMP signaling in nociceptive processing. cGMP levels in the spinal cord are controlled by the concerted action of a number of PDE isoforms, which can be present in the same cell.

Cyclic nucleotide phosphodiesterases as targets for treatment of haematological malignancies

The cAMP signalling pathway has emerged as a key regulator of haematopoietic cell proliferation, differentiation and apoptosis. In parallel, general understanding of the biology of cyclic nucleotide PDEs (phosphodiesterases) has advanced considerably, revealing the remarkable complexity of this enzyme system that regulates the amplitude, kinetics and location of intracellular cAMP-mediated signalling. The development of therapeutic inhibitors of specific PDE gene families has resulted in a growing appreciation of the potential therapeutic application of PDE inhibitors to the treatment of immune-mediated illnesses and haematopoietic malignancies. This review summarizes the expression and function of PDEs in normal haematopoietic cells and the evidence that family-specific inhibitors will be therapeutically useful in myeloid and lymphoid malignancies.

Phosphodiesterase 5 (PDE 5) inhibitors for the treatment of male erectile disorder: Attaining selectivity versus PDE6

The role of phosphodiesterase type 5 (PDE5) in the mechanism of male erection has been well understood, and several drugs inhibiting this enzyme are being used for the treatment of erectile dysfunction (ED). Discovery of inhibitors with improved selectivity versus other PDE isozymes could lead to drugs with improved safety profile. Achievement of selectivity versus PDE6, co-inhibition of which results in disturbances of color perception, remains the most challenging aspect of current drug discovery programs. The present review describes several case studies, where significant (>100 fold) selectivity versus PDE6 has been attained via investigation of structure-activity relationships (SAR). Special attention is given to the chemical routes leading to novel chemotypes and allowing efficient exploration of their SAR's. Strategies for attaining inhibitor selectivity discussed below may be applicable for other drug discovery programs.

Inhibition of phosphodiesterase 1 augments the pulmonary vasodilator response to inhaled nitric oxide in awake lambs with acute pulmonary hypertension

Phosphodiesterase 1 (PDE1) modulates vascular tone and the development of tolerance to nitric oxide (NO)-releasing drugs in the systemic circulation. Any role of PDE1 in the pulmonary circulation remains largely uncertain. We measured the expression of genes encoding PDE1 isozymes in the pulmonary vasculature and examined whether or not selective inhibition of PDE1 by vinpocetine attenuates pulmonary hypertension and augments the pulmonary vasodilator response to inhaled NO in lambs. Using RT-PCR, we detected PDE1A, PDE1B, and PDE1C mRNAs in pulmonary arteries and veins isolated from healthy lambs. In 13 lambs, the thromboxane A(2) analog U-46619 was infused intravenously to increase mean pulmonary arterial pressure to 35 mmHg. Four animals received an intravenous infusion of vinpocetine at incremental doses of 0.3, 1, and 3 mg.kg(-1).h(-1). In nine lambs, inhaled NO was administered in a random order at 2, 5, 10, and 20 ppm before and after an intravenous infusion of 1 mg.kg(-1).h(-1) vinpocetine. Administration of vinpocetine did not alter pulmonary and systemic hemodynamics or transpulmonary cGMP or cAMP release. Inhaled NO selectively reduced mean pulmonary arterial pressure, pulmonary capillary pressure, and pulmonary vascular resistance index, while increasing transpulmonary cGMP release. The addition of vinpocetine enhanced pulmonary vasodilation and transpulmonary cGMP release induced by NO breathing without causing systemic vasodilation but did not prolong the duration of pulmonary vasodilation after NO inhalation was discontinued. Our findings demonstrate that selective inhibition of PDE1 augments the therapeutic efficacy of inhaled NO in an ovine model of acute chemically induced pulmonary hypertension.

Signalling via cGMP: lessons from Drosophila

Guanosine 3', 5'-cyclic monophosphate (cGMP) signalling has received increasing attention over the last decade, since the discovery of the gaseous signalling molecule, nitric oxide, which activates cGMP synthesis. Furthermore, research into cGMP signalling has also been stimulated by the development of Viagra and pharmacologically active related compounds, which act to prevent cGMP breakdown. While much is known about the biochemical aspects of components of the cGMP signalling pathway, the precise in vivo roles of such components have only recently come to light through work in model organisms. This review outlines recent work utilising the genetic model organism Drosophila melanogaster in studies of organotypic cGMP signalling. While organisms such as Drosophila may not be the obvious choice for such studies, use of this model has proved that unique and detailed insights for cGMP signalling can be achieved.

Cyclic nucleotide phosphodiesterase (PDE) superfamily: a new target for the development of specific therapeutic agents

Cyclic nucleotide phosphodiesterases (PDEs), which are ubiquitously distributed in mammalian tissues, play a major role in cell signaling by hydrolyzing cAMP and cGMP. Due to their diversity, which allows specific distribution at cellular and subcellular levels, PDEs can selectively regulate various cellular functions. Their critical role in intracellular signaling has recently designated them as new therapeutic targets for inflammation. The PDE superfamily represents 11 gene families (PDE1 to PDE11). Each family encompasses 1 to 4 distinct genes, to give more than 20 genes in mammals encoding the more than 50 different PDE proteins probably produced in mammalian cells. Although PDE1 to PDE6 were the first well-characterized isoforms because of their predominance in various tissues and cells, their specific contribution to tissue function and their regulation in pathophysiology remain open research fields. This concerns particularly the newly discovered families, PDE7 to PDE11, for which roles are not yet established. In many pathologies, such as inflammation, neurodegeneration, and cancer, alterations in intracellular signaling related to PDE deregulation may explain the difficulties observed in the prevention and treatment of these pathologies. By inhibiting specifically the up-regulated PDE isozyme(s) with newly synthesized potent and isozyme-selective PDE inhibitors, it may be potentially possible to restore normal intracellular signaling selectively, providing therapy with reduced adverse effects.

Ca2+-calmodulin-dependent phosphodiesterase (PDE1): Current perspectives

Ca2+-calmodulin-dependent phosphodiesterases (PDE1), like Ca2+-sensitive adenylyl cyclases (AC), are key enzymes that play a pivotal role in mediating the cross-talk between cAMP and Ca2+ signalling. Our understanding of how ACs respond to Ca2+ has advanced greatly, with significant breakthroughs at both the molecular and functional level. By contrast, little is known of the mechanisms that might underlie the regulation of PDE1 by Ca2+ in the intact cell. In living cells, Ca2+ signals are complex and diverse, exhibiting different spatial and temporal properties. The potential therefore exists for dynamic changes in the subcellular distribution and activation of PDE1 in relation to intracellular Ca2+ dynamics. PDE1s are a large family of multiply-spliced gene products. Therefore, it is possible that a cell-type specific response to elevation in [Ca2+]i can occur, depending on the isoform of PDE1 expressed. In this article, we summarize current knowledge on Ca2+ regulation of PDE1 in the intact cell and discuss approaches that might be undertaken to delineate the responses of this important group of enzymes to changes in [Ca2+]i.

Cyclic nucleotide phosphodiesterases in Drosophila melanogaster

Cyclic nucleotide PDEs (phosphodiesterases) are important enzymes that regulate intracellular levels of cAMP and cGMP. In the present study, we identify and characterize novel PDEs in the genetic model, Drosophila melanogaster. The Drosophila genome encodes five novel PDE genes in addition to dunce. Predicted PDE sequences of Drosophila show highly conserved critical domains when compared with human PDEs. Thus PDE-encoding genes of D. melanogaster are CG14940-PDE1C, CG8279-PDE6beta, CG5411-PDE8A, CG32648-PDE9 and CG10231-PDE11. Reverse transcriptase-PCRs of adult tissues reveal widespread expression of PDE genes. Drosophila Malpighian (renal) tubules express all the six PDEs: Drosophila PDE1, dunce (PDE4), PDE6, PDE8, PDE9 and PDE11. Antipeptide antibodies were raised against PDE1, PDE6, PDE9 and PDE11. Verification of antibody specificity by Western blotting of cloned and expressed PDE constructs allowed the immunoprecipitation studies of adult Drosophila lysates. Biochemical characterization of immunoprecipitated endogenous PDEs showed that PDE1 is a dual-specificity PDE (Michaelis constant Km for cGMP: 15.3+/-1 microM; Km cAMP: 20.5+/-1.5 microM), PDE6 is a cGMP-specific PDE (Km cGMP: 37+/-13 microM) and PDE11 is a dual-specificity PDE (Km cGMP: 6+/-2 microM; Km cAMP: 18.5+/-5.5 microM). Drosophila PDE1, PDE6 and PDE11 display sensitivity to vertebrate PDE inhibitors, zaprinast (IC50 was 71+/-39 microM for PDE1, 0.65+/-0.015 microM for PDE6 and 1.6+/-0.5 microM for PDE11) and sildenafil (IC50 was 1.3+/-0.9 microM for PDE1, 0.025+/-0.005 microM for PDE6 and 0.12+/-0.06 microM for PDE11). We provide the first characterization of a cGMP-specific PDE and two dual-specificity PDEs in Drosophila, and show a high degree of similarity in structure and function between human and Drosophila PDEs.

Phosphodiesterases in the vascular system

Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) are second messengers involved in the intracellular signal transduction of a variety of extracellular stimuli in several tissues. In the vascular system, these nucleotides play important roles in the regulation of vascular tone and in the maintenance of the mature contractile phenotype in smooth muscle cells. Given that cyclic nucleotide signaling regulates a wide variety of cellular functions, it is not surprising that cyclic nucleotide phosphodiesterases (PDEs). In paticular, the accumulating data showing that there are a large number of different PDE isozymes have triggered an equally large increase in interest about these enzymes. At least 11 different gene families of PDEs are currently known to exist in mammalian tissues. Most families contain several distinct genes, and many of these genes are expressed in different tissues as functionally unique alternative splice variants. This article reviews many of the important aspects about the structure, cellular localization, and regulation of each family of PDEs. Particular emphasis is placed on new information obtained in the last few years about vascular disease. The development of novel methods to deliver more potent and selective PDE inhibitors to individual cell types and subcellular locations will lead to new therapeutic uses for this class of drugs in diseases of the vascular system.

cGMP-phosphodiesterase activity is up-regulated in response to pressure overload of rat ventricles

Although expression of natriuretic peptides in cardiac tissues is up-regulated in response to pressure overload, no significant change in cGMP level in hypertrophied ventricles was observed. Activities of two cyclic nucleotide phosphodiesterase (PDE) isoforms, Ca2+/calmodulin-stimulated PDE (PDE1) and cGMP-stimulated PDE (PDE2), were significantly higher in rat left ventricles 14 days after aortic banding. The absence of significant changes in PDE1A and PDE2A mRNA levels indicated that the two PDE activities were post-transcriptionally up-regulated. These results suggested that the increased cGMP-PDE activity in response to pressure overload plays an important role in neutralizing cGMP action in cardiac tissue.

Cloning and characterization of a novel apolipoprotein A-I binding protein, AI-BP, secreted by cells of the kidney proximal tubules in response to HDL or ApoA-I

Apolipoprotein A-I (apoA-I) is the major apolipoprotein of high-density lipoproteins (HDL) and has an important role in the regulation of the stability, lipid transport, and metabolism of HDL particles. To identify novel proteins that are involved in HDL metabolism, we used mature apoA-I (amino acids 25-267) as a bait for the screening of a human liver two-hybrid cDNA library. Among the identified genes, several encoded known proteins, including serum amyloid A(2a) (SAA(2a)), apoC-I, and phosphodiesterase HCAM1 (PDE1A), found to interact with apoA-I. In addition, we have cloned a novel 29 kDa apoA-I interacting protein, which we named AI-BP (apoA-I binding protein). The AI-BP encoding gene, APOA1BP, which is located on chromosome 1q21, is composed of six exons and five introns and spans 2.5 kb. Northern blot analysis demonstrated ubiquitous expression of the APOA1BP mRNA with the highest expression in kidney, heart, liver, thyroid gland, adrenal gland, and testis. AI-BP protein is not detectable in serum of healthy probands, but serum samples of patients with septic syndromes may contain elevated levels of AI-BP. Significant amounts of AI-BP protein are found in cerebrospinal fluid and urine of healthy probands. The stimulation of cells derived from the kidney proximal tubules with apoA-I or HDL induces a concentration-dependent secretion of AI-BP indicating an important role for AI-BP, in the renal tubular degradation or resorption of apoA-I.

Reciprocal regulation of calcium dependent and calcium independent cyclic AMP hydrolysis by protein phosphorylation

The hydrolysis of cyclic nucleotide second messengers takes place through multiple cyclic nucleotide phosphodiesterases (PDEs). The significance of this diversification is not fully understood. Here we report the differential regulation of low K(m) Ca2+-activated (PDE1C) and Ca2+-independent, rolipram-sensitive (PDE4) PDEs by protein phosphorylation in the neuroendocrine cell line AtT20. Incubation of cells with 8-(4-chlorophenylthio)-cyclic AMP (CPT-cAMP) enhanced PDE4 and reduced PDE1C activity. These effects were blocked by H89 indicating mediation by cAMP-dependent protein kinase (PKA), furthermore in broken cell preparations PKA produced the same reciprocal changes of PDE activities. Calyculin A, an inhibitor of protein phosphatases 1 and 2 A, stimulated PDE4 and enhanced the inhibitory effect of CPT-cAMP on PDE1C. The reduction of PDE1C activity was characterized by a marked attenuation of the activation by Ca2+/calmodulin. Stimulation of PDE4 activity by CPT-cAMP or calyculin A was attributable to PDE4D3 and these effects could also be reproduced in human embryonic kidney cells expressing epitope-tagged PDE4D3. Together, these data show reciprocal regulation of PDE1C and PDE4D by PKA, which represents a novel scheme for plasticity in intracellular signalling.

Cyclic nucleotide phosphodiesterase 1C promotes human arterial smooth muscle cell proliferation

Proliferation of arterial smooth muscle cells (SMCs) is a key event in the formation of advanced atherosclerotic lesions and restenosis after angioplasty. Cyclic nucleotides (cAMP and cGMP) inhibit arterial SMC proliferation, and elevation of cyclic nucleotides reduces neointimal formation after angioplasty in animal models. Degradation of cAMP and cGMP is catalyzed by cyclic nucleotide phosphodiesterases (PDEs). One of these, PDE1C, hydrolyzes cAMP and cGMP and is expressed in proliferating human SMCs but is absent in quiescent human aorta. Thus, PDE1C expression is low in cultured human SMCs made quiescent by attaching to fibrillar collagen type I. After release from the fibrillar collagen, PDE1C expression is induced and associated with traverse through S-phase of the cell cycle. Further, PDE1C is expressed in vivo in human fetal aorta containing proliferating SMCs, but not in newborn aorta in which SMC proliferation has ceased. Inhibition of PDE1C in SMCs isolated from normal aorta or from lesions of atherosclerosis using antisense oligonucleotides or a PDE1 inhibitor results in suppression of SMC proliferation. In conclusion, PDE1C expression is a marker of human SMC proliferation ex vivo and in vivo. Inhibition of PDE1C leads to inhibition of human SMC proliferation. Because PDE1C is absent in quiescent SMCs, PDE1C inhibitors may target proliferating SMCs in lesions of atherosclerosis or restenosis.

Isolation and differential tissue distribution of two human cDNAs encoding PDE1 splice variants

A cDNA selection technique has been used to isolate full-length human cDNAs of the phosphodiesterase 1 (PDE1) calcium calmodulin (CaM)-regulated phosphodiesterase gene family. We isolated cDNAs representing multiple splice variants of PDE1A, 1B and 1C from a variety of tissues. Included among these were two novel splice variants for PDE1A and 1B. The first, PDE1A5, encodes a 519-residue protein, which is different from PDE1A1 by the insertion of 14 residues, a divergent carboxy terminus and also differs from PDE1A3 through a divergent amino terminus. Our second novel splice variant represents the first occurrence of a splice variant of the PDE1B gene. PDE1B2 encodes a 516-residue protein and diverges from PDE1B1 by the replacement of the first 38 residues by an alternative 18, which is predicted to be functionally significant. Using the splice variant sequence differences to perform comparative Northern analysis, we have demonstrated that each variant has a differential tissue distribution.

Cloning of dog heart PDE1A - a first detailed characterization at the molecular level in this species

The dog, as a model for cardiovascular function, has been widely used in the pharmacological analysis of PDE inhibitors, particularly those thought to target the heart. However biochemical analyses of dog heart PDE have been largely performed on mixed enzyme populations, sequence information is lacking and no PDE from dog heart has been cloned. We have characterized a completely purified PDE1 enzyme from dog heart using dye-affinity, Mono-Q and calmodulin-affinity chromatography. The enzyme was stimulated 3-4-fold by calmodulin ([S]=0.5 microM) and, in the absence of calmodulin, exhibited biphasic kinetics with a low K(m) of 1.2 microM and 0.53 microM for cAMP and cGMP, with respective V(max) values of 283 and 146 nmoles min(-1) mg(-1). Internal peptides from this enzyme were used to design degenerate PCR primers. Subsequent 3'-RACE, 5'-RACE and high fidelity PCR were then used to produce a full length gene identified as PDE1A1 by sequence identity to human and bovine sequences. Northern analysis using the dog heart cDNA as a probe suggested the presence of an additional form of PDE1, in heart only, separate from the PDE1A group which was present in both heart and skeletal muscle. Multiple forms of human PDE1A are known to exist and PDE1B is present in human heart muscle. The findings here extend the PDE1 data to the dog and contribute to our understanding of the molecular biology of PDE1A in this species.

In vivo assessment of local phosphodiesterase activity using tailored cyclic nucleotide-gated channels as cAMP sensors

Phosphodiesterases (PDEs) catalyze the hydrolysis of the second messengers cAMP and cGMP. However, little is known about how PDE activity regulates cyclic nucleotide signals in vivo because, outside of specialized cells, there are few methods with the appropriate spatial and temporal resolution to measure cyclic nucleotide concentrations. We have previously demonstrated that adenovirus-expressed, olfactory cyclic nucleotide-gated channels provide real-time sensors for cAMP produced in subcellular compartments of restricted diffusion near the plasma membrane (Rich, T.C., K.A. Fagan, H. Nakata, J. Schaack, D.M.F. Cooper, and J.W. Karpen. 2000. J. Gen. Physiol. 116:147-161). To increase the utility of this method, we have modified the channel, increasing both its cAMP sensitivity and specificity, as well as removing regulation by Ca(2)+-calmodulin. We verified the increased sensitivity of these constructs in excised membrane patches, and in vivo by monitoring cAMP-induced Ca(2)+ influx through the channels in cell populations. The improved cAMP sensors were used to monitor changes in local cAMP concentration induced by adenylyl cyclase activators in the presence and absence of PDE inhibitors. This approach allowed us to identify localized PDE types in both nonexcitable HEK-293 and excitable GH4C1 cells. We have also developed a quantitative framework for estimating the K(I) of PDE inhibitors in vivo. The results indicate that PDE type IV regulates local cAMP levels in HEK-293 cells. In GH4C1 cells, inhibitors specific to PDE types I and IV increased local cAMP levels. The results suggest that in these cells PDE type IV has a high K(m) for cAMP, whereas PDE type I has a low K(m) for cAMP. Furthermore, in GH4C1 cells, basal adenylyl cyclase activity was readily observable after application of PDE type I inhibitors, indicating that there is a constant synthesis and hydrolysis of cAMP in subcellular compartments near the plasma membrane. Modulation of constitutively active adenylyl cyclase and PDE would allow for rapid control of cAMP-regulated processes such as cellular excitability.

Increased cGMP phosphodiesterase activity mediates renal resistance to ANP in rats with bile duct ligation

BACKGROUND

Liver disease resulting from common bile duct ligation (CBDL) causes abnormal sodium metabolism that is manifested by resistance to the natriuretic action of atrial natriuretic peptide (ANP). This resistance is corrected both in vitro and in vivo by zaprinast, a selective inhibitor of a guanosine cyclic-3'-5'-monophosphate (cGMP)-specific phosphodiesterase (PDE5). Several other PDEs with affinity for cGMP are expressed in kidney and could also be involved in this response.

METHODS

We measured cGMP hydrolysis in inner medullary collecting duct (IMCD) cell homogenates from kidneys of sham-operated and CBDL rats and quantitated the amount of PDE5 protein by Western blotting and immunoprecipitation studies. We also characterized ANP responsiveness in vivo of kidneys of anesthetized sham and CBDL rats by measuring sodium excretion before and after volume expansion (VE).

RESULTS

Kinetic analysis of PDE5 activity in homogenates of IMCD cells isolated from kidneys of sham-operated rats indicated a Vmax of 85.3 +/- 1.7 versus 157 +/- 2.9 pmol/mg/min from CBDL rats (P < 0.01), without a difference in Km. Enzyme activity was inhibited competitively by 1,3-dimethyl-6-(2-propoxy-5-methanesulfonylamidophenyl)pyrazol[3,4d]-pyrimidin-4-(5H)-one (DMPPO), a potent and specific inhibitor of PDE5, with an apparent Ki of 4.5 +/- 0.7 and 4.9 +/- 0.7 nmol/L and an IC50 of 6.1 +/- 0.8 and 8.7 +/- 0.7 nmol/L in sham and CBDL rats, respectively (P = NS). DMPPO exhibited very poor inhibitory activity against the calcium-calmodulin-dependent PDE1 in IMCD homogenates from sham rats (Ki 1.3 +/- 0.1 micromol/L and IC50 1.9 +/- 0.2 micromol/L). Western analysis using an antiserum made against bovine lung PDE5 revealed a twofold increase in PDE5 protein in cytosolic extracts from IMCD of CBDL rat kidneys compared with sham-operated controls, and immunoprecipitation studies indicated that the increase in PDE5 protein accounted for the observed increase in cGMP hydrolysis. DMPPO (10 nmol/L) normalized the blunted ANP-dependent cGMP accumulation by IMCD cells from CBDL rats in vitro. Intrarenal infusion of DMPPO (0.5 nmol/min) in CBDL rats corrected both the impaired natriuretic response to VE and the blunted VE-related increase in urinary cGMP excretion from the infused, but not the contralateral kidney.

CONCLUSION

These results demonstrate that renal resistance to ANP in CBDL rats is accompanied by heightened activity of PDE5, which is due largely to an increase in PDE5 protein. Other PDEs could contribute only a minor part to the enhanced cGMP hydrolysis observed in kidneys of CBDL rats. This PDE5-dependent ANP resistance may represent an important contributor to the sodium retention of liver disease.

Diazepam and rolipram differentially inhibit cyclic AMP-specific phosphodiesterases PDE4A1 and PDE4B3 in the mouse

Cyclic AMP is hydrolyzed by members of at least eight classes of cyclic nucleotide phosphodiesterases (PDEs). Although it has been reported that cyclic AMP PDE activity in mammalian tissues can be inhibited by benzodiazepines, it has not been conclusively demonstrated that members of the class of cyclic AMP-specific, rolipram-inhibitable PDEs (PDE4s) are targets for these drugs. Moreover, no PDE4s expressed in mice have been characterized. To address these issues, we isolated two cDNAs representing homologues of PDE4A1 and PDE4B3 from a mouse brain library. After transient transfection in human embryonic kidney (HEK) 293 cells, the mouse PDEs hydrolyzed cyclic AMP with a low K(m) and were inhibited by rolipram; both are properties typical of other mammalian PDE4 enzymes. In addition, we found that diazepam inhibited cyclic AMP hydrolysis by the mouse PDE4 subtypes. Interestingly, PDE4B was significantly more sensitive to inhibition by both rolipram and diazepam than the PDE4A subtype. This is the first demonstration that recombinantly expressed PDE4s are inhibited by diazepam, and should facilitate future studies with mouse models of depression and anxiety.

Identification and characterization of DdPDE3, a cGMP-selective phosphodiesterase from Dictyostelium

In Dictyostelium cAMP and cGMP have important functions as first and second messengers in chemotaxis and development. Two cyclic-nucleotide phosphodiesterases (DdPDE 1 and 2) have been identified previously, an extracellular dual-specificity enzyme and an intracellular cAMP-specific enzyme (encoded by the psdA and regA genes respectively). Biochemical data suggest the presence of at least one cGMP-specific phosphodiesterase (PDE) that is activated by cGMP. Using bioinformatics we identified a partial sequence in the Dictyostelium expressed sequence tag database that shows a high degree of amino acid sequence identity with mammalian PDE catalytic domains (DdPDE3). The deduced amino acid sequence of a full-length DdPDE3 cDNA isolated in this study predicts a 60 kDa protein with a 300-residue C-terminal PDE catalytic domain, which is preceded by approx. 200 residues rich in asparagine and glutamine residues. Expression of the DdPDE3 catalytic domain in Escherichia coli shows that the enzyme has Michaelis-Menten kinetics and a higher affinity for cGMP (K(m)=0.22 microM) than for cAMP (K(m)=145 microM); cGMP does not stimulate enzyme activity. The enzyme requires bivalent cations for activity; Mn(2+) is preferred to Mg(2+), whereas Ca(2+) yields no activity. DdPDE3 is inhibited by 3-isobutyl-1-methylxanthine with an IC(50) of approx. 60 microM. Overexpression of the DdPDE3 catalytic domain in Dictyostelium confirms these kinetic properties without indications of its activation by cGMP. The properties of DdPDE3 resemble those of mammalian PDE9, which also shows the highest sequence similarity within the catalytic domains. DdPDE3 is the first cGMP-selective PDE identified in lower eukaryotes.

Human Ca2+/calmodulin-dependent phosphodiesterase PDE1A: novel splice variants, their specific expression, genomic organization, and chromosomal localization

We report here the identification of novel human PDE1A splice variants, their tissue distribution patterns, genomic structure, and chromosomal localization of the gene. We identified one N-terminus (N3) and one C-terminus (C3) by cDNA library screening and dbEST database search. These N- and C-termini, including the reported N-termini (N1 and N2) and C-termini (C1 and C2), combined to generate nine different PDE1A cDNAs. N1 and N2 are similar to the 5' ends of the bovine PDE1A proteins of 61 kDa and 59 kDa, respectively, and C1 and C2 are the 3' ends of the reported human PDE1A variants. The results of PCR and Southern blot analysis show that nine PDE1A splice variants exhibit distinctive tissue distribution patterns by the difference of the N-terminus. PDE1As with N2 were widely expressed in various tissues, mainly in the kidney, liver, and pancreas. On the other hand, PDE1As with N1 and N3 were particularly expressed at a high level in the brain and testis, respectively. These findings suggest that the distinct expression patterns among PDE1A variants depend on the several promoters situated upstream of exons encoding 5' ends of the variants. The PDE1A gene spans over 120 kb of genomic DNA, and consists of at least 17 exons and 16 introns. The PDE1A gene was located on human chromosome 2q32 by fluorescent in situ hybridization analysis.

Mechanism of transducin activation of frog rod photoreceptor phosphodiesterase. Allosteric interactiona between the inhibitory gamma subunit and the noncatalytic cGMP-binding sites

The rod photoreceptor phosphodiesterase (PDE) is unique among all known vertebrate PDE families for several reasons. It is a catalytic heterodimer (alphabeta); it is directly activated by a G-protein, transducin; and its active sites are regulated by inhibitory gamma subunits. Rod PDE binds cGMP at two noncatalytic sites on the alphabeta dimer, but their function is unclear. We show that transducin activation of frog rod PDE introduces functional heterogeneity to both the noncatalytic and catalytic sites. Upon PDE activation, one noncatalytic site is converted from a high affinity to low affinity state, whereas the second binding site undergoes modest decreases in binding. Addition of gamma to transducin-activated PDE can restore high affinity binding as well as reducing cGMP exchange kinetics at both sites. A strong correlation exists between cGMP binding and gamma binding to activated PDE; dissociation of bound cGMP accompanies gamma dissociation from PDE, whereas addition of either cGMP or gamma to alphabeta dimers can restore high affinity binding of the other molecule. At the active site, transducin can activate PDE to about one-half the turnover number for catalytic alphabeta dimers completely lacking bound gamma subunit. These results suggest a mechanism in which transducin interacts primarily with one PDE catalytic subunit, releasing its full catalytic activity as well as inducing rapid cGMP dissociation from one noncatalytic site. The state of occupancy of the noncatalytic sites on PDE determines whether gamma remains bound to activated PDE or dissociates from the holoenzyme, and may be relevant to light adaptation in photoreceptor cells.

The molecular biology of cyclic nucleotide phosphodiesterases

Recent progress in the field of cyclic nucleotides has shown that a large array of closely related proteins is involved in each step of the signal transduction cascade. Nine families of adenylyl cyclases catalyze the synthesis of the second messenger cAMP, and protein kinases A, the intracellular effectors of cAMP, are composed of four regulatory and three catalytic subunits. A comparable heterogeneity has been discovered for the enzymes involved in the inactivation of cyclic nucleotide signaling. In mammals, 19 different genes encode the cyclic nucleotide phosphodiesterases (PDEs), the enzymes that hydrolyze and inactivate cAMP and cGMP. This is only an initial level of complexity, because each PDE gene contains several distinct transcriptional units that give rise to proteins with subtle structural differences, bringing the number of the PDE proteins close to 50. The molecular biology of PDEs in Drosophila and Dictyostelium has shed some light on the role of PDE diversity in signaling and development. However, much needs to be done to understand the exact function of these enzymes, particularly during mammalian development and cell differentiation. With the identification and mapping of regulatory and targeting domains of the PDEs, modularity of the PDE structure is becoming an established tenet in the PDE field. The use of different transcriptional units and exon splicing of a single PDE gene generates proteins with different regulatory domains joined to a common catalytic domain, therefore expanding the array of isoforms with subtle differences in properties and sensitivities to different signals. The physiological context in which these different isoforms function is still largely unknown and undoubtedly will be a major area of expansion in the years to come.

The calcium/calmodulin-dependent phosphodiesterase PDE1C down-regulates glucose-induced insulin secretion

To understand the role cAMP phosphodiesterases (PDEs) play in the regulation of insulin secretion, we analyzed cyclic nucleotide PDEs of a pancreatic beta-cell line and used family and isozyme-specific PDE inhibitors to identify the PDEs that counteract glucose-stimulated insulin secretion. We demonstrate the presence of soluble PDE1C, PDE4A and 4D, a cGMP-specific PDE, and of particulate PDE3, activities in betaTC3 insulinoma cells. Selective inhibition of PDE1C, but not of PDE4, augmented glucose-stimulated insulin secretion in a dose-dependent fashion thus demonstrating that PDE1C is the major PDE counteracting glucose-dependent insulin secretion from betaTC3 cells. In pancreatic islets, inhibition of both PDE1C and PDE3 augmented glucose-dependent insulin secretion. The PDE1C of betaTC3 cells is a novel isozyme possessing a K(m) of 0.47 microM for cAMP and 0.25 microM for cGMP. The PDE1C isozyme of betaTC3 cells is sensitive to 8-methoxymethyl isobutylmethylxanthine and zaprinast (IC(50) = 7.5 and 4.5 microM, respectively) and resistant to vinpocetine (IC(50) > 100 microM). Increased responsiveness of PDE1C activity to calcium/calmodulin is evident upon exposure of cells to glucose. Enhanced cAMP degradation by PDE1C, due to increases in its responsiveness to calcium/calmodulin and in intracellular calcium, constitutes a glucose-dependent feedback mechanism for the control of insulin secretion.

Isolation, expression and analysis of splice variants of a human Ca2+/calmodulin-stimulated phosphodiesterase (PDE1A)

The PDE1A gene encodes a Ca2+/calmodulin-stimulated 3',5'-cyclic nucleotide phosphodiesterase (PDE). We have performed 5' and 3' RACE and identified two additional 5'-splice variants and one additional 3'-splice variant of the human PDE1A gene. The three known 5'-splice variants and the two known 3'-splice variants combine to generate six different PDE1A mRNAs. However, one of the 5'-splice variants exhibits alternate splicing in the 5' untranslated region. Thus the six mRNAs encode four different PDE1A proteins. Recombinant forms of the different human PDE1A isoforms were expressed in Sf9 cells. The kinetic properties and inhibitor sensitivities of the four PDE1A isoforms are very similar to one another.

Isolation and characterization of PDE10A, a novel human 3', 5'-cyclic nucleotide phosphodiesterase

A gene encoding a novel human 3', 5'-cyclic nucleotide phosphodiesterase (PDE) was identified and characterized. PDE10A1 encodes a protein that is 779 amino acids in length. An incomplete cDNA for a second 5'-splice variant, PDE10A2, was isolated. The proteins encoded by the two variants share 766 amino acids in common. This common region includes an amino-terminal domain with partial homology to the cGMP-binding domains of PDE2, PDE5 and PDE6 as well as a carboxy-terminal region with homology to the catalytic regions of mammalian PDEs. Northern analysis revealed that PDE10A is widely expressed. The PDE10A gene was mapped to three yeast artificial chromosomes (YACs) that contain human DNA from chromosome 6q26-27. A recombinant protein corresponding to the 766 amino acid region common to PDE10A1 and PDE10A2 was expressed in yeast. It hydrolyzed both cAMP and cGMP. Inhibitors that are selective for other PDE families are poor inhibitors of PDE10A; however, PDE10A is inhibited by the non-specific PDE inhibitor, IBMX.

A critical role of the nitric oxide/cGMP pathway in corticostriatal long-term depression

High-frequency stimulation (HFS) of corticostriatal glutamatergic fibers induces long-term depression (LTD) of excitatory synaptic potentials recorded from striatal spiny neurons. This form of LTD can be mimicked by zaprinast, a selective inhibitor of cGMP phosphodiesterases (PDEs). Biochemical analysis shows that most of the striatal cGMP PDE activity is calmodulin-dependent and inhibited by zaprinast. The zaprinast-induced LTD occludes further depression by tetanic stimulation and vice versa. Both forms of synaptic plasticity are blocked by intracellular 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylyl cyclase, indicating that an increased cGMP production in the spiny neuron is a key step. Accordingly, intracellular cGMP, activating protein kinase G (PKG), also induces LTD. Nitric oxide synthase (NOS) inhibitors N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) and 7-nitroindazole monosodium salt (7-NINA) block LTD induced by either HFS or zaprinast, but not that induced by cGMP. LTD is also induced by the NO donors S-nitroso-N-acetylpenicillamine (SNAP) and hydroxylamine. SNAP-induced LTD occludes further depression by HFS or zaprinast, and it is blocked by intracellular ODQ but not by L-NAME. Intracellular application of PKG inhibitors blocks LTD induced by HFS, zaprinast, and SNAP. Electron microscopy immunocytochemistry shows the presence of NOS-positive terminals of striatal interneurons forming synaptic contacts with dendrites of spiny neurons. These findings represent the first demonstration that the NO/cGMP pathway exerts a feed-forward control on the corticostriatal synaptic plasticity.

Phosphodiesterase 4 inhibitors as airways smooth muscle relaxant agents: synthesis and biological activities of triazine derivatives

A series of triazine derivatives was synthesized. The compounds were evaluated for tracheal smooth muscle relaxant and type 4 phosphodiesterase inhibitory activities. A highly significant correlation was observed between the two effects. Two compounds exhibited potent relaxant activity (EC50: 17 and 24 nM) and might be useful for the treatment of asthma.

Identification of inhibitor specificity determinants in a mammalian phosphodiesterase

Mammalian phosphodiesterase types 3 and 4 (PDE3 and PDE4) hydrolyze cAMP and are essential for the regulation of this intracellular second messenger in many cell types. Whereas these enzymes share structural and biochemical similarities, each can be distinguished by its sensitivity to isozyme-specific inhibitors. By using a series of chimeric enzymes, we have localized the region of PDE4 that confers sensitivity to selective inhibitors. This inhibitor specificity domain lies within a short sequence at the carboxyl terminus of the catalytic domain of the protein, consistent with the competitive nature of inhibition by these compounds. Surprisingly, the identified region also includes some of the most highly conserved residues among PDE isoforms. A yeast-based expression system was used for the isolation and characterization of mutations within this area that confer resistance to the PDE4-specific inhibitor rolipram. Analysis of these mutants indicated that both conserved and unique residues are required for isoform-specific inhibitor sensitivity. In some cases, combined point mutations contribute synergistically to the reduction of sensitivity (suppression of IC50). We also report that several mutations display differential sensitivity changes with respect to distinct structural classes of inhibitors.

Isolation and characterization of cDNAs encoding PDE5A, a human cGMP-binding, cGMP-specific 3',5'-cyclic nucleotide phosphodiesterase

Human cGMP-binding, cGMP-specific 3',5'-cyclic nucleotide phosphodiesterase (PDE5A) cDNAs were isolated. A 3.1-kb composite DNA sequence assembled from overlapping cDNAs encodes an 875-amino-acid protein with a predicted molecular mass of 100012 Da (PDE5A1). Extracts prepared from yeast expressing human PDE5A1 hydrolyzed cGMP. This activity was inhibited by the selective PDE5 inhibitors zaprinast and DMPPO. PDE5A mRNA is expressed in aortic smooth muscle cells, heart, placenta, skeletal muscle and pancreas and, to a much lesser extent, in brain, liver and lung. A 5'-splice variant, PDE5A2, encodes an 833-amino-acid protein with eight unique amino acids at the amino terminus. PDE5A maps to chromosome 4q 25-27.

Identification and characterization of the human homologue of the short PDE4A cAMP-specific phosphodiesterase RD1 (PDE4A1) by analysis of the human HSPDE4A gene locus located at chromosome 19p13.2

The HSPDE4A gene spans 50 kb, consists of at least 17 exons and is orientated 5'-3', telomere to centromere. It is located at chromosome 19p13.2, being 350 kb proximal to the gene encoding TYK2 and 850 kb distal to the gene encoding the low-density lipoprotein receptor. Its structure is consistent with the production of active 'long' and 'short' isoenzymes as the result of alternative mRNA splicing at two splice junctions. Identified is the single alternatively spliced 5' exon encoding the unique N-terminal region of the long isoenzyme HSPDE4A4B (pde46). The upstream conserved regions, UCR1 and UCR2, which form characteristic domains of PDE4 long forms are each encoded by three exons. The PDE4A-subfamily-specific linker region LR1, which joins UCR1 and UCR2, is encoded by two exons, whereas LR2, which joins UCR2 to the catalytic unit, is encoded by a single exon. Identification of exons encoding an enzymically inactive product of this gene, HSPDE4A8A (2el), indicates that this is an authentic gene product. The 5' exon encoding the unique N-terminal region of the human homologue of the rodent isoform RNPDE4A1A (RD1) was located, and the splice junction used to produce this short PDE4A isoform shown to occur at a different position from that seen in both the rat PDE4B and PDE4D genes. Reverse transcriptase PCR analysis indicates that RD1 homologues are conserved across species, having a conserved membrane-targeting region and a hypervariable LR2 region. Human RD1 was expressed transiently in COS-7 cells and detected as an 83 kDa species primarily associated with the high-speed membrane fraction. Human RD1 exhibited a Km for cAMP of about 3 microM, an IC50 value for inhibition by the PDE4-selective inhibitor rolipram of about 0.3 microM and was considerably more thermostable than rat RD1. Human RD1 was generated as a mature 80 kDa species in an in vitro transcription-translation system and shown to be capable of binding to membranes. Knowledge of the gene structure and the associated sequence information should facilitate analysis of the involvement of PDE4A in hereditary disorders that may result from alterations in enzyme expression, activity, regulation and intracellular targeting and serve as a resource for determining authenticity of cloned PDE4A species.

Developmental changes in lung cGMP phosphodiesterase-5 activity, protein, and message

During transitional circulation, the pulmonary vascular bed undergoes a rapid and profound reduction in both tone and vascular smooth-muscle (VSM) content. 3',5'-Guanylate cyclic monophosphate (cGMP) is a crucial mediator in the regulation of pulmonary vascular resistance (PVR) and VSM proliferation. Hydrolysis of cGMP is achieved predominately by cGMP-specific phosphodiesterases (PDEs). Among the cGMP-specific PDEs, PDE5 is quantitatively prevalent in lung tissue. We have investigated the levels of pulmonary PDE5 enzymatic activity, protein, and messenger RNA (mRNA) in ovine and mouse lung during perinatal development. We report that within 1 h following birth, PDE5 activity, protein, and mRNA levels decrease in both species, in a manner that correlates with known decreases in PVR in early transition. However, from 4 to 7 d following birth, a secondary increase in PDE5 activity, protein, and mRNA occurs in both ovine and mouse lung, suggesting a complex regulation of PVR and VSM proliferation in late perinatal development. Our data imply that PDE5 may be an important mediator in the regulation of PVR in normal and possibly in pathologic states, and may ultimately provide a basis for PDE5 inhibitors as a treatment for pulmonary hypertension.

Yeast model system for study of mammalian phosphodiesterases

Facile manipulation and rapid regeneration have helped to establish the yeast Saccharomyces cerevisiae as a genetic workhorse. More recently, these simple eukaryotes have been used for the biochemical analysis of mammalian proteins. This article describes the use of a yeast expression system for both in vitro and in vivo assays of mammalian phosphodiesterase (PDE) activity using yeast cells devoid of endogenous PDEs. It also presents simple methodologies for the analysis of the pharmacological properties of mammalian PDEs and describes the use of a powerful genetic selection for mutant forms of PDEs with altered biochemical and pharmacological characteristics.

Identification, quantitation, and cellular localization of PDE1 calmodulin-stimulated cyclic nucleotide phosphodiesterases

The calmodulin-stimulated cyclic nucleotide phosphodiesterases (PDE1s) constitute a large gene family and are found in a wide variety of tissues and cells. Because of the functional diversity of PDE1 genes and the observation that these isozymes often make up a major component of the total cyclic nucleotide hydrolytic activity in certain cell types, PDE1s are of growing interest as targets for therapeutic intervention. Here we describe a series of methodologies to identify, quantitate, and determine the cellular expression of PDE1 isozymes. We describe first the resolution of different PDEs using high-performance anion-exchange chromatography and then a Western blotting methodology for identifying or authenticating PDE1 activities. Next we present an immunoprecipitation method that can be used for quantitating specific PDE1 isoforms and describe the use of RNase protection analysis for further identification of PDE1 subtypes. Finally, we provide a simple, immunocytochemical method for determining the cellular expression of PDE1 isozymes. Combined, the above methodologies should allow an investigator to identify, quantitate, and determine the cellular localization of PDE1 isozymes in any tissue with little ambiguity.

Characterization of five different proteins produced by alternatively spliced mRNAs from the human cAMP-specific phosphodiesterase PDE4D gene

We have isolated and characterized complete cDNAs for two isoforms (HSPDE4D4 and HSPDE4A5) encoded by the human PDE4D gene, one of four genes that encode cAMP-specific rolipram-inhibited 3',5'-cyclic nucleotide phosphodiesterases (type IVPDEs; PDE4 family). The HSPDE4D4 and HSPDE4D5 cDNAs encode proteins of 810 and 746 amino acids respectively. A comparison of the nucleotide sequences of these two cDNAs with those encoding the three other human PDE4D proteins (HSPDE4D1, HSPDE4D2 and HSPDE4D3) demonstrates that each corresponding mRNA transcript has a unique region of sequence at or near its 5'-end, consistent with alternative mRNA splicing. Transient expression of the five cDNAs in monkey COS-7 cells produced proteins of apparent molecular mass under denaturing conditions of 68, 68, 95, 119 and 105 kDa for isoforms HSPDE4D1-5 respectively. Immunoblotting of human cell lines and rat brain demonstrated the presence of species that co-migrated with the proteins produced in COS-7 cells. COS-cell-expressed and native HSPDE4D1 and HSPDE4D2 were found to exist only in the cytosol, whereas HSPDE4D3, HSPDE4D4 and HSPDE4D5 were found in both cytosolic and particulate fractions. The IC50 values for the selective PDE4 inhibitor rolipram for the cytosolic forms of the five enzymes were similar (0.05-0.14 microM), whereas they were 2-7-fold higher for the particulate forms of HSPDE4D3 and HSPDE4D5 (0.32 and 0.59 microM respectively), than for the corresponding cytosolic forms. Our data indicate that the N-terminal regions of the HSPDE4D3, HSPDE4D4 and HSPDE4D5 proteins, which are derived from alternatively spliced regions of their mRNAs, are important in determining their subcellular localization, activity and differential sensitivity to inhibitors.

Calmodulin-stimulated cyclic nucleotide phosphodiesterase (PDE1C) is induced in human arterial smooth muscle cells of the synthetic, proliferative phenotype

The diversity among cyclic nucleotide phosphodiesterases provides multiple mechanisms for regulation of cAMP and cGMP in the cardiovascular system. Here we report that a calmodulin-stimulated phosphodiesterase (PDE1C) is highly expressed in proliferating human arterial smooth muscle cells (SMCs) in primary culture, but not in the quiescent SMCs of intact human aorta. High levels of PDE1C were found in primary cultures of SMCs derived from explants of human newborn and adult aortas, and in SMCs cultured from severe atherosclerotic lesions. PDE1C was the major cAMP hydrolytic activity in these SMCs. PDE expression patterns in primary SMC cultures from monkey and rat aortas were different from those from human cells. In monkey, high expression of PDE1B was found, whereas PDE1C was not detected. In rat SMCs, PDE1A was the only detectable calmodulin-stimulated PDE. These findings suggest that many of the commonly used animal species may not provide good models for studying the roles of PDEs in proliferation of human SMCs. More importantly, the observation that PDE1C is induced only in proliferating SMCs suggests that it may be both an indicator of proliferation and a possible target for treatment of atherosclerosis or restenosis after angioplasty, conditions in which proliferation of arterial SMCs is negatively modulated by cyclic nucleotides.

Identification and characterisation of a human calmodulin-stimulated phosphodiesterase PDE1B1

A cDNA encoding a calmodulin-stimulated 3',5'-cyclic nucleotide phosphodiesterase (PDE) was isolated from a human brain cDNA library. The cDNA, designated HSPDE1B1, encoded a protein of 536 amino acids that shared 96% sequence identity with the bovine "63 kDa" calmodulin-stimulated PDE. The recombinant protein had cyclic nucleotide phosphodiesterase activity that was stimulated approximately 2-fold by Ca2+/calmodulin and preferred cGMP as substrate. In addition, the enzymatic activity of HSPDE1B1 was inhibited by phosphodiesterase inhibitors with potencies similar to that displayed toward the bovine PDE1 enzymes: IBMX approximately equal to 8-methoxymethyl-IBMX > vinpocetine approximately equal to zaprinast > cilostamide > rolipram. HSPDE1B1 mRNA was found predominantly in the brain. Lower mRNA levels were found in heart and skeletal muscle. In situ hybridisation of brain revealed expression of HSPDE1B1 predominately in neuronal cells of the cerebellum, hippocampus and caudate. The HSPDE1B1 gene was mapped to human chromosome 12. A partial genomic sequence of HSPDE1B1 was isolated and shown to contain two splice junctions that are conserved in the rat PDE4 and the Drosophila dunce genes.

Alternative splicing of the high affinity cAMP-specific phosphodiesterase (PDE7A) mRNA in human skeletal muscle and heart

To further our understanding of the structure and function of phosphodiesterases of the newly identified family of high affinity cAMP-specific phosphodiesterases (PDE7), we identified and characterized the isozyme expressed in human skeletal muscle and the protein product of the previously isolated isozyme HCP1 (designated HSPDE7A1). We report the isolation of a cDNA encoding the full-length skeletal muscle isoform of human PDE7A (HSPDE7A2). The DNA sequence of this skeletal muscle cDNA indicates that PDE7A2 is a novel 5' splice variant of PDE7A encoding an isoform with a novel, hydrophobic N terminus. The 456-amino acid PDE7A2 protein is detected on Western blots as a band with an apparent mobility of 50 kDa. PDE7A2 is a high affinity cAMP-specific PDE (Km = 0.1 microM), which is localized to particulate cellular fractions. The PDE7A1 (HCP1) isozyme is detected on Western blots as a band with an apparent mobility of 57 kDa, demonstrating that the previously isolated HCP1 cDNA encodes the full-length PDE7A1 protein. The even distribution of PDE7A mRNA among fetal tissues and the relative abundance of its two mRNAs strongly suggest that the expression of PDE7A is regulated throughout development.

Isolation and characterization of human cDNAs encoding a cGMP-stimulated 3',5'-cyclic nucleotide phosphodiesterase

Human cyclic GMP-stimulated 3',5'-cyclic nucleotide phosphodiesterase (PDE2A3) cDNAs were cloned from hippocampus and fetal brain cDNA libraries. A 4.2-kb composite DNA sequence constructed from overlapping cDNA clones encodes a 941 amino acid protein with a predicted molecular mass of 105,715 Da. Extracts prepared from yeast expressing the human PDE2A3 hydrolyzed both cyclic AMP (cAMP) and cyclic GMP (cGMP). This activity was inhibited by EHNA, a selective PDE2 inhibitor, and was stimulated three-fold by cGMP. Human PDE2A is expressed in brain and to a lesser extent in heart, placenta, lung, skeletal muscle, kidney and pancreas. The human PDE2A3 differs from the bovine PDE2A1 and rat PDE2A2 proteins at the amino terminus but its amino-terminal sequence is identical to the bovine PDE2A3 sequence. The different amino termini probably arise from alternative exon splicing of the PDE2A mRNA.

Challenge of human Jurkat T-cells with the adenylate cyclase activator forskolin elicits major changes in cAMP phosphodiesterase (PDE) expression by up-regulating PDE3 and inducing PDE4D1 and PDE4D2 splice variants as well as down-regulating a novel PDE4A splice variant

The cAMP phosphodiesterase (PDE) 3 and PDE4 isoforms provide the major cAMP-hydrolysing PDE activities in Jurkat T-cells, with additional contributions from the PDE1 and PDE2 isoforms. Challenge of cells with the adenylate cyclase activator forskolin led to a rapid, albeit transient, increase in PDE3 activity occurring over the first 45 min, followed by a sustained increase in PDE3 activity which began after approximately 3 h and continued for at least 24 h. Only this second phase of increase in PDE3 activity was blocked by the transcriptional inhibitor actinomycin D. After approximately 3 h of exposure to forskolin, PDE4 activity had increased, via a process that could be inhibited by actinomycin D, and it remained elevated for at least a 24 h period. Such actions of forskolin were mimicked by cholera toxin and 8-bromo-cAMP. Forskolin increased intracellular cAMP concentrations in a time-dependent fashion and its action was enhanced when PDE induction was blocked with actinomycin D. Reverse transcription (RT)-PCR analysis, using generic primers designed to detect transcripts representing enzymically active products of the four PDE4 genes, identified transcripts for PDE4A and PDE4D but not for PDE4B or PDE4C in untreated Jurkat T-cells. Forskolin treatment did not induce transcripts for either PDE4B or PDE4C; however, it reduced the RT-PCR signal for PDE4A transcripts and markedly enhanced that for PDE4D transcripts. Using RT-PCR primers for PDE4 splice variants, a weak signal for PDE4D1 was evident in control cells whereas, in forskolin-treated cells, clear signals for both PDE4D1 and PDE4D2 were detected. RT-PCR analysis of the PDE4A species indicated that it was not the PDE4A isoform PDE-46 (PDE4A4B). Immunoblotting of control cells for PDE4 forms identified a single PDE4A species of approximately 118 kDa, which migrated distinctly from the PDE4A4B isoform PDE-46, with immunoprecipitation analyses showing that it provided all of the PDE4 activity in control cells. Forskolin treatment led to a marked decrease of this novel PDE4A species and allowed the detection of a strong signal for an approximately 67 kDa PDE4D species, suggested to be PDE4D1, but did not induce PDE4B and PDE4C isoforms. Elevation of intracellular cAMP concentrations in Jurkat T-cells thus exerts a highly selective effect on the transcriptional activity of the genes encoding the various PDE4 isoforms. This leads to the down-regulation of a novel PDE4A splice variant and the induction of PDE4D1 and PDE4D2 splice variants, leading to a net increase in the total PDE4 activity of Jurkat T-cells.

Receptor-mediated stimulation of lipid signalling pathways in CHO cells elicits the rapid transient induction of the PDE1B isoform of Ca2+/calmodulin-stimulated cAMP phosphodiesterase

Chinese hamster ovary cells (CHO cells) do not exhibit any Ca2+/calmodulin-stimulated cAMP phosphodiesterase (PDE1) activity. Challenge of CHO cells with agonists for endogenous P2-purinoceptors, lysophosphatidic acid receptors and thrombin receptors caused a similar rapid transient induction of PDE1 activity in each instance. This was also evident on noradrenaline challenge of a cloned CHO cell line transfected so as to overexpress alpha 1B-adrenoceptors. This novel PDE1 activity appeared within about 15 min of exposure to ligands, rose to a maximum value within 30 min to 1 h and then rapidly decreased. In each case, the expression of novel PDE1 activity was blocked by the transcriptional inhibitor actinomycin D. Challenge with insulin of either native CHO cells or a CHO cell line transfected so as to overexpress the human insulin receptor failed to induce PDE1 activity. Reverse transcriptase-PCR analyses, using degenerate primers able to detect the PDE1C isoform, did not amplify any fragment from RNA preparations of CHO cells expressing PDE1 activity, although they did so from the human thyroid carcinoma FTC133 cell line. Reverse transcriptase-PCR analyses, using degenerate primers able to detect the PDE1A and PDE1B isoforms, successfully amplified a fragment of the predicted size from RNA preparations of both CHO cells expressing PDE1 activity and human Jurkat T-cells. Sequencing of the PCR products, generated using the PDE1A/B primers, yielded a novel sequence which, by analogy with sequences reported for bovine and murine PDE1B forms, suggests that the PDE1 species induced in CHO cells through protein kinase C activation and that expressed in Jurkat T-cells are PDE1B forms.

Intracellular localization of the PDE4A cAMP-specific phosphodiesterase splice variant RD1 (RNPDE4A1A) in stably transfected human thyroid carcinoma FTC cell lines

Cells of two human follicular thyroid carcinoma cell lines (FTC133, FTC236) were stably transfected with a cDNA encoding the PDE4A cAMP-specific phosphodiesterase (PDE) splice variant RD1 (RNPDE4A1A) so as to generate the cloned cell lines, FTC133A and FTC236A. This allowed the expression of a novel rolipram-inhibited cAMP-specific PDE activity in these cells. Unlike the parent cell lines in which Ca2+/calmodulin caused a profound activation (approx. 3-4-fold) of homogenate PDE activity, no such stimulation was evident in the RD1-expressing cell lines, indicating loss of PDE1 activity. Reverse transcriptase-PCR analysis indicated that this was due to the down-regulation of the PDE1C isoform. The novel PDE4 activity in transfected cells was located exclusively in the membrane fraction, as was immunoreactive RD1. Low concentrations of the detergent Triton X-100, but not high NaCl concentrations, allowed RD1 to be solubilized. Laser scanning confocal immunofluorescence analyses identified RD1 immunoreactivity in a discrete perinuclear region of these RD1-expressing transfected cell lines. A similar pattern of labelling was observed using the antiserum Tex1, which specifically identified the Golgi apparatus. Treatment of FTC133A cells with the Golgi-perturbing agents monensin and brefeldin A led to a similar redistribution of immunoreactive species detected using both the Tex1 and anti-RD1 antisera. It is suggested that the PDE4A splice variant RD1 contains a membrane-association signal which allows the targeted expression of RD1 within the Golgi complex of these human follicular thyroid carcinoma cell lines.

Inhibition of calmodulin-dependent phosphodiesterase induces apoptosis in human leukemic cells

Cytosolic extracts from a human lymphoblastoid B-cell line, RPMI-8392, established from a patient with acute lymphocytic leukemia, contain two major forms of cyclic nucleotide phosphodiesterase (PDE): Ca2+-calmodulin dependent PDE (PDE1) and cAMP-specific PDE (PDE4). In contrast, normal quiescent human peripheral blood lymphocytes (HPBL) are devoid of PDE1 activity [Epstein, P. M., Moraski, S., Jr., and Hachisu, R. (1987) Biochem. J. 243, 533-539]. Using reverse transcription-polymerase chain reaction (RT-PCR), we show that the mRNA encoding the 63-kDa form of PDE1 (PDE1B1) is expressed in RPMI-8392 cells, but not in normal, resting HPBL. This mRNA is, however, induced in HPBL following mitogenic stimulation by phytohemagglutinin (PHA). Also using RT-PCR, the full open reading frame for human PDE1B1 cDNA was cloned from RPMI-8392 cells and it encodes a protein of 536 amino acids with 96% identity to bovine, rat, and mouse species. RT-PCR also identifies the presence of PDE1B1 in other human lymphoblastoid and leukemic cell lines of B- (RPMI-1788, Daudi) and T-(MOLT-4, NA, Jurkat) cell origin. Inhibition of PDE1 or PDE4 activity by selective inhibitors induced RPMI-8392 cells, as well as the other cell lines, to undergo apoptosis. Culture of RPMI-8392 cells with an 18-bp phosphorothioate antisense oligodeoxynucleotide, targeted against the translation initiation region of the RPMI-8392 mRNA, led to a specific reduction in the amount of PDE1B1 mRNA after 1 day, and its disappearance after 2 days, and induced apoptosis in these cells in a sequence specific manner. This suggests that PDEs, particularly PDE1B1, because its expression is selective, may be useful targets for inducing the death of leukemic cells.