Systematic search for single nucleotide polymorphisms in the 5' flanking region of the human phosphodiesterase 3B gene: absence of evidence for major effects of identified polymorphisms on susceptibility to Japanese type 2 diabetes

The activation of phosphodiesterase 3B (PDE3B) reduces free fatty acid output from adipocytes. A reduced PDE3B gene expression could lead to insulin resistance. To determine whether there are polymorphisms associated with type 2 diabetes in PDE3B gene promoter, this 5(') flanking region was isolated. The transcription initiation site was located 206bp upstream from the translation start site. Sequences of 2kb of the 5(') flanking region for 24 type 2 diabetic Japanese subjects were initially analyzed using PCR direct sequencing, and the regions including the identified polymorphisms were then examined. In 98 controls and 98 type 2 diabetic subjects, -1947T>C, -567G>A, -465G>T, -458T>C, and -1727_-1726insTCAATT were found. Only -465G>T and this insertion had more than 5% frequencies. Since a complete linkage disequilibrium existed between them, -465G>T was further analyzed, along with a previously identified +1389G>A in the coding region, in a total of 200 controls and 207 type 2 diabetic subjects. These allele frequencies were not significantly different between these two groups (controls vs. cases; -465G>T, 12.0% vs. 10.1%, P=0.435; +1389G>A, 30.3% vs. 33.3%, P=0.408). These genotype distributions were not significantly different between these two groups. The T/T genotype at -465 was rare although this frequency could be higher in type 2 diabetes (4/207 subjects) than controls (0/200 subjects). The linkage disequilibrium existed between -465G>T and +1389G>A, and the estimated haplotype frequencies defined by these SNPs were not significantly different between the cases and controls. Thus, the identified polymorphisms are unlikely to have major effects on susceptibility to Japanese type 2 diabetes.

IGF-I-induced differentiation of L6 myogenic cells requires the activity of cAMP-phosphodiesterase

Inhibition of type 4 cAMP-specific phosphodiesterase (PDE4) activity in L6-C5 and L6-E9 abolished myogenic differentiation induced by low-serum medium and IGF-I. L6-C5 cells cultured in low-serum medium displayed a PDE4 activity higher than cells cultured in serum-free medium, a condition not sufficient to induce differentiation. In the presence of serum, PDE4D3, the major isoform natively expressed in L6-C5 cells, translocated to a Triton-insoluble fraction, which increased the PDE specific activity of the fraction, and exhibited a Mr shift typical of phosphorylation of this isoform. Furthermore, serum promoted the localization of PDE4D3 to a vesicular subcellular compartment. In L6-C5 cells, IGF-I is a stronger inducer of myogenic differentiation in the presence than in absence of serum. Its ability to trigger differentiation in the absence of serum was restored by overexpressing wild-type PDE4D3, but not a phosphorylation-insensitive mutant. This finding was confirmed in single cells overexpressing a GFP-PDE4D3 fusion protein by assessing nuclear accumulation of myogenin in both L6-C5 and L6-E9. Overexpression of other PDE isoforms was less efficient, confirming that PDE4D3 is the physiologically relevant phosphodiesterase isoform in the control of myogenesis. These results show that downregulation of cAMP signaling through cAMP-phosphodiesterase stimulation is a prerequisite for induction of myogenesis.

Contrasting activities of the aggregative and late PDSA promoters in Dictyostelium development

Expression of the Dictyostelium PdsA gene from the aggregative (PdA) and late (PdL) promoter is essential for aggregation and slug morphogenesis, respectively. We studied the regulation of the PdA and PdL promoters in slugs using labile beta-galactosidase (gal) reporter enzymes. PdL was active in prestalk cells as was also found with stable gal. PdA activity decreased strongly in slugs from all cells, except those at the rear. This is almost opposite to PdA activity traced with stable gal, where slugs showed sustained activity with highest levels at the front. PdA was down-regulated after aggregation irrespective of stimulation with any of the factors known to control gene expression. PdL activity was induced in cell suspension by cAMP and DIF acting in synergy. However, a DIF-less mutant showed normal PdL activity during development, suggesting that DIF does not control PdL in vivo. Dissection of the PdL promoter showed that all sequences essential for correct spatiotemporal control of promoter activity are downstream of the transcription start site in a region between -383 and -19 nucleotides relative to the start codon. Removal of nucleotides to position -364 eliminated responsiveness to DIF and cAMP, but normal PdL activity in prestalk cells in slugs was retained. Further 5' deletions abolished all promoter activity. This result also indicates that the induction by DIF and cAMP as seen in cell suspensions is not essential for PdL activity in normal development.

Molecular cloning and subcellular distribution of the novel PDE4B4 cAMP-specific phosphodiesterase isoform

We have isolated cDNAs encoding PDE4B4, a new cAMP-specific phosphodiesterase (PDE4) isoform with novel properties. The amino acid sequence of PDE4B4 demonstrates that it is encoded by the PDE4B gene, but that it differs from the previously isolated PDE4B1, PDE4B2 and PDE4B3 isoforms by the presence of a novel N-terminal region of 17 amino acids. PDE4B4 contains both of the upstream conserved region 1 (UCR1) and UCR2 regulatory units that are characteristic of 'long' PDE4 isoforms. RNase protection demonstrated that PDE4B4 mRNA is expressed preferentially in liver, skeletal muscle and various regions of the brain, which differs from the pattern of tissue distribution of the other known PDE4B long forms, PDE4B1 and PDE4B3. Expression of PDE4B4 cDNA in COS7 cells produced a protein of 85 kDa under denaturing conditions. Subcellular fractionation of recombinant, COS7-cell expressed PDE4B4 showed that the protein was localized within the cytosol, which was confirmed by confocal microscopic analysis of living COS7 cells transfected with a green fluorescent protein-PDE4B4 chimaera. PDE4B4 exhibited a K(m) for cAMP of 5.4 microM and a V(max), relative to that of the long PDE4B1 isoform, of 2.1. PDE4B4 was inhibited by the prototypical PDE4 inhibitor rolipram [4-[3-(cyclopentoxyl)-4-methoxyphenyl]-2-pyrrolidinone] with an IC(50) of 83 nM. Treatment of COS7 cells with forskolin, to elevate cAMP levels, produced activation of PDE4B4, which was associated with the phosphorylation of PDE4B4 on Ser-56 within UCR1. The unique tissue distribution and intracellular targeting of PDE4B4 suggests that this isoform may have a distinct functional role in regulating cAMP levels in specific cell types.

Identification and distribution of different mRNA variants produced by differential splicing in the human phosphodiesterase 9A gene

The transcript population of the human gene coding for a cGMP-dependent phosphodiesterase (PDE9A) has a complex structure. There is a high level of mRNA in intestinal and prostate tissues, a low level in blood, and intermediate in other tissues. More than 20 different variants produced by differential splicing have been observed and new exons have been identified both by PCR amplification and by the analysis of available EST sequences. In all cases the transcriptional start site is the same and no differential splicing is found in the exons coding for the catalytic domain of the protein. In some cases the protein produced by splice variants is truncated. The distribution of the splice variants is not homogeneous among the different tissues studied. The human, but not the mouse, PDE9A gene appears to have a complex regulation of expression by different isoforms.

Ubiquitous expression of phosphodiesterase 7A in human proinflammatory and immune cells

We have determined the expression of phosphodiesterase (PDE) 7A1 and PDE7A2 in human cells that have been implicated in the pathogenesis of chronic obstructive pulmonary disease and asthma. Messenger RNA transcripts were detected by RT-PCR in T lymphocytes, monocytes, neutrophils, airway and vascular smooth muscle cells, lung fibroblasts, epithelial cells, and cardiac myocytes. Human epithelial, T cell, eosinophil, and lung fibroblast cell lines were also positive for PDE7A1 and PDE7A2 mRNA transcripts. By Western immunoblot analyses the amount of PDE7A1 was greatest in T cell lines, peripheral blood T lymphocytes, epithelial cell lines, airway and vascular smooth muscle cells, lung fibroblasts, and eosinophils but was not detected in neutrophils. In contrast, PDE7A2 protein, which was identified in human cardiac myocytes, was not found in any of the other cell types investigated. Immunoconfocal analyses showed that PDE7A was expressed in neutrophils and alveolar macrophages. As the expression of PDE7A mirrors the distribution of PDE4 we speculate that this enzyme could be a target for novel anti-inflammatory drugs.

PDE3 cyclic nucleotide phosphodiesterases and the compartmentation of cyclic nucleotide-mediated signalling in cardiac myocytes

PDE3 cyclic nucleotide phosphodiesterase inhibitors raise cAMP and cGMP content in cardiac and vascular myocytes. Their administration to patients with dilated cardiomyopathy leads to improvements in hemodynamic parameters in the short term but reduces survival with chronic administration. The reasons for this 'biphasic' response have not been elucidated, but it is likely that beneficial and harmful effects of PDE3 inhibition reflect the phosphorylation of different substrates of cAMP- and cGMP-dependent protein kinases (PK-A and PK-G). It is now apparent that cardiac and vascular myocytes contain several isoforms of PDE3 that differ in their intracellular distribution and thus regulate cAMP and cGMP levels in different subcellular compartments. These isoforms also differ in their regulation by extracellular signals that may be important in the pathophysiology of dilated cardiomyopathy. An intriguing possibility is that the beneficial and harmful effects of PDE3 inhibition may be attributable to the inhibition of different isoforms of these enzymes.

Increased expression of the cGMP-inhibited cAMP-specific (PDE3) and cGMP binding cGMP-specific (PDE5) phosphodiesterases in models of pulmonary hypertension

1. Chronic hypoxic treatment of rats (to induce pulmonary hypertension, PHT) for 14 days increased cGMP-inhibited cAMP specific phosphodiesterase (PDE3) and cGMP binding cGMP specific phosphodiesterase (PDE5) activities in pulmonary arteries. The objective of this study was to establish the molecular basis for these changes in both animal and cell models of PHT. In this regard, RT-PCR and quantitative Western blotting analysis was applied to rat pulmonary artery homogenates and human pulmonary "artery" smooth muscle cell (HPASMC) lysates. 2. PDE3A/B gene transcript levels were increased in the main, first, intrapulmonary and resistance pulmonary arteries by chronic hypoxia. mRNA transcript and protein levels of PDE5A2 in the main and first branch pulmonary arteries were also increased by chronic hypoxia, with no effect on PDE5A1/A2 in the intra-pulmonary and resistance vessels. 3. The expression of PDE3A was increased in HPASMCs maintained under chronic hypoxic conditions for 14 days. This may be mediated via a protein kinase A-dependent mechanism, as treatment of cells with Br-cAMP (100 microM) mimicked chronic hypoxia in increasing PDE3A expression, while the PKA inhibitor, H8 peptide (50 microM) abolished the hypoxic-dependent increase in PDE3A transcript. 4. We also found that the treatment of HPASMCs with the inhibitor of kappaB degradation Tosyl-Leucyl-Chloro-Ketone (TLCK, 50 microM) reduced PDE5 transcript levels, suggesting a role for this transcription factor in the regulation of PDE5 gene expression. 5. Our results show that increased expression of PDE3 and PDE5 might explain some changes in vascular reactivity of pulmonary vessels from rats with PHT. We also report that NF-kappaB might regulate basal PDE5 expression.

Interleukin-1beta induces phosphodiesterase 4B2 expression in human myometrial cells through a prostaglandin E2- and cyclic adenosine 3',5'-monophosphate-dependent pathway

Intrauterine infections are important etiological factors of preterm labor. They trigger an increase in proinflammatory cytokines, in particular IL-1beta, that induces a cascade of events resulting in the production of potent effectors of myometrial contractility, such as the prostaglandin E(2) (PGE(2)). Within the smooth muscle cells, contractility is under the control of cAMP content, partly regulated by cAMP-phosphodiesterase 4 (PDE4), the predominant family of PDEs expressed in human myometrium. In the present study, using a model of inflammation of human myometrial cells in culture, we demonstrated that exposing the cells to IL-1beta resulted in a significant up-regulation of PDE4 activity through an increase in PDE4B2 mRNA and protein levels. The IL-1beta-induced PDE4 activity occurs after an increase in PGE(2) production and subsequent cAMP augmentation. Pretreatment with indomethacin or NS 398 completely blocked this long-term effect of IL-1beta, revealing a PGE(2)-dependent pathway. Accordingly, our results demonstrated that the PDE4B2 variant can participate in the regulation of the inflammatory reaction that occurs at term or in preterm labor and leads to myometrial contractions. Knowing the myorelaxant effect of PDE4 inhibitors and the implication of the PDE4B2 in the inflammatory process, this isoform may be an appropriate target for discovering antiinflammatory drugs to manage infection-induced preterm deliveries.

Cyclic nucleotide phosphodiesterase isozymes expressed in mouse skeletal muscle

To understand changes in cyclic nucleotide metabolism in muscle disease states, the expression of phosphodiesterase (PDE) isozymes in normal mouse leg muscle was examined. Four subcellular fractions were generated by differential centrifugation at 10,000 x g and 100,000 x g. cAMP PDE activity was found predominately in the soluble fractions, while cGMP PDE activity was more evenly distributed amongst soluble and particulate fractions. Pharmacological inhibitors demonstrate that PDE4 represents the major cAMP hydrolyzing activity and PDE2 represents the major cGMP hydrolyzing activity in mouse leg muscle. PDE1 is expressed at low levels, while PDE3 and PDE5 are intermediate. Between 20 and 40% of total PDE activity remained in the presence of inhibitors for PDE1-PDE5, indicating that other PDE families contribute to the total PDE pool. Reverse-transcription PCR with family-specific primers showed expression of mRNA for PDE7-PDE9, supporting this conclusion. Total PDE activity was found to be elevated in tissue extracts from a mouse model of Duchenne's muscular dystrophy.

DMSO-treated HL60 cells: a model of neutrophil-like cells mainly expressing PDE4B subtype

The human promyelocytic HL60 cells acquired a neutrophilic phenotype after a 7- to 10-day DMSO treatment. Fc gammaRII was up-regulated. Fc gammaRI was also up-regulated by an additional IFN-gamma treatment. These cells are able to produce O2*- by NADPH oxidase activation in the presence of immune complexes or phorbol-12-myristate-13-acetate (PMA). A change of their PDE4 subtype profile was also observed: PDE4B was the predominant isoenzyme, PDE4D was down-regulated and PDE4A was no longer detectable. Additionally, the more NADPH oxidase was activated by PMA, the less PDE4A was expressed, suggesting that NADPH oxidase activity could be used as a surrogate marker of PDE4A down-regulation. Rolipram and Ariflo (cilomilast), two selective PDE4 inhibitors, dose-dependently inhibited receptor-coupled activation of superoxide. These results suggest that PDE4B is the main subtype involved in regulating superoxide induced by Fc gammaRs activation. Furthermore, these cells, expressing almost exclusively PDE4B subtype, could be useful to identify selective PDE4B inhibitors.

Characterization of phosphodiesterase 3 in human malignant melanoma cell line

Little is known concerning the expression, distribution and function of phosphodiesterase (PDE) 3s in malignant tumor cells, including human malignant melanoma HMG and osteosarcoma HOSM-1 cells. PDE3 activity was detected in homogenates of HMG cells; however, much less activity was found in HOSM-1 cells. In HMG cells, most of the PDE3 activity was in the particulate fraction. PDE3A and 3B mRNAs were detected by RT-PCR in RNA from HMG cells only. The nucleotide sequences of the fragments were identical to those of human PDE3A and 3B. The PDE3-specific inhibitors, trequinsin and cilostamide, did not inhibit the proliferation of HMG or HOSM-1 cells. Although two PDE3 isoforms may be expressed in human malignant melanoma cells, their functional importance is not known.

Inhibition of human phosphodiesterase 4A expressed in yeast cell GL62 by theophylline, rolipram, and acetamide-45

AIM

To study the inductive expression of human phosphodiesterase 4A (hPDE4A) in yeast cell GL62 and investigate the inhibitory effects of theophylline, rolipram, and acetamide-45 on PDE4A activity of the expressed product in yeast cell GL62.

METHODS

Yeast cell GL62 were transfected with human PDE4A gene cloned in the expression plasmid p138NB. Expression was induced by adding CuSO4 to a final concentration of 150 micromol/L, and the expressed product was extracted. The activity of PDE4A was detected by HPLC.

RESULTS

Yeast cell GL62 expressed a certain protein at CuSO4 150 micromol/L, the size of the expressed product was between 62 kDa and 83 kDa, the activity of PDE4A of the expressed product at 3 h was in maximum (188 23) micromol/g/min, and the Km was (17.7 2.6) micromol/L. Theophylline, rolipram, and acetamide-45 could inhibit the activity of PDE4A extracted from yeast cell GL62. The IC50 (95 % confidence limits) of theophylline, rolipram, and acetamide-45 were 1642 (989-2727), 4.58 (3.45-6.08), and 275 (170-444) micromol/L respectively.

CONCLUSION

PDE4A expressed in yeast cell GL62 is biologically active. Theophylline, rolipram, and acetamide-45 can inhibit the PDE4A activity. The expressed product in yeast cell GL62 may be used in the research work of PDE4 and its inhibitors.

Differential regulation of gene expression and insulin-induced activation of phosphodiesterase 3B in adipocytes of lean insulin-resistant IRS-1 (-/-) mice

Phosphodiesterase (PDE) 3B, a major isoform of PDE in adipocytes, mediates the antilipolytic action of insulin. PDE3B gene expression is generally reduced in adipocytes of either monogenic or polygenic rodent models of obese, insulin-resistance. An increased fat cell size, a common feature of obesity, could account for this reduction. Insulin receptor substrate-1 (IRS-1) (-/-) mice are lean with a reduced fat cell size and have insulin resistance due to a primary defect of insulin signaling. To determine whether the regulation of PDE3B gene expression is correlated with fat cell size, we examined this gene expression in adipose tissues of IRS-1 (-/-) mice. In IRS-1 (-/-) mice, PDE3B mRNA and protein levels were increased 1.24- and 1.35-fold those in C57BL/6J control mice, respectively. Independently, the fold induction of PDE activity by insulin (insulin-induced/basal) was 1.7-fold in control mice, but was reduced to 1.35-fold in IRS-1 (-/-) mice. Thus, PDE3B gene expression may be inversely correlated with a fat cell size, whereas insulin-induced PDE3B activation is mediated through IRS-1.

Targeting of cyclic AMP degradation to beta 2-adrenergic receptors by beta-arrestins

Catecholamines signal through the beta2-adrenergic receptor by promoting production of the second messenger adenosine 3',5'-monophosphate (cAMP). The magnitude of this signal is restricted by desensitization of the receptors through their binding to beta-arrestins and by cAMP degradation by phosphodiesterase (PDE) enzymes. We show that beta-arrestins coordinate both processes by recruiting PDEs to activated beta2-adrenergic receptors in the plasma membrane of mammalian cells. In doing so, the beta-arrestins limit activation of membrane-associated cAMP-activated protein kinase by simultaneously slowing the rate of cAMP production through receptor desensitization and increasing the rate of its degradation at the membrane.

Isoforms of cyclic nucleotide phosphodiesterase PDE3A in cardiac myocytes

PDE3A cyclic nucleotide phosphodiesterases regulate cAMP- and cGMP-mediated intracellular signaling in cardiac myocytes. We used antibodies to different regions of PDE3A to demonstrate the presence of three PDE3A isoforms in these cells. These isoforms, whose apparent molecular weights are 136,000, 118,000, and 94,000 ("PDE3A-136," "PDE3A-118," and "PDE3A-94"), are identical save for the deletion of different lengths of N-terminal sequence containing two membrane-association domains and sites for phosphorylation/activation by protein kinase B ("PK-B") and protein kinase A ("PK-A"). PDE3A-136 contains both membrane-association domains and the PK-B and PK-A sites. PDE3A-118 contains only the downstream membrane-association domain and the PK-A sites. PDE3A-94 lacks both membrane localization domains and the PK-B and PK-A sites. The three isoforms are translated from two mRNAs derived from the PDE3A1 gene: PDE3A-136 is translated from PDE3A1 mRNA, whereas PDE3A-118 and PDE3A-94 are translated from PDE3A2 mRNA. Experiments involving in vitro transcription/translation indicate that PDE3A-118 and PDE3A-94 may be translated from different AUGs in PDE3A2 mRNA. These findings suggest that alternative transcriptional and post-transcriptional processing of the PDE3A gene results in the generation of two mRNAs and three protein isoforms in cardiac myocytes that differ with respect to intracellular localization and may be regulated through different signaling pathways.

Genomic organization, chromosomal localization, and alternative splicing of the human phosphodiesterase 8B gene

We have characterized the gene for human phosphodiesterase 8B, PDE8B, and cloned the full-length cDNA for human PDE8B (PDE8B1) and two splice variants (PDE8B2 and PDE8B3). The PDE8B gene is mapped to the long arm of chromosome 5 (5q13) and is composed of 22 exons spanning over approximately 200kb. The donor and acceptor splice site sequences match the consensus sequences for the exon-intron boundaries of most eukaryotic genes. PDE8B1 encodes an 885 amino acid enzyme, containing an N-terminal REC domain, a PAS domain, and a C-terminal catalytic domain. PDE8B2 and PDE8B3 both have deletion in the PAS domain and encode 838 and 788 amino acid proteins, respectively. RT-PCR analysis revealed that while PDE8B1 is the most abundant variant in thyroid gland, PDE8B3, but not PDE8B1, is the most abundant form in brain. These findings suggest that selective usage of exons produces three different PDE8B variants that exhibit a tissue-specific expression pattern.

Important role of phosphodiesterase 3B for the stimulatory action of cAMP on pancreatic beta-cell exocytosis and release of insulin

Cyclic AMP potentiates glucose-stimulated insulin release and mediates the stimulatory effects of hormones such as glucagon-like peptide 1 (GLP-1) on pancreatic beta-cells. By inhibition of cAMP-degrading phosphodiesterase (PDE) and, in particular, selective inhibition of PDE3 activity, stimulatory effects on insulin secretion have been observed. Molecular and functional information on beta-cell PDE3 is, however, scarce. To provide such information, we have studied the specific effects of the PDE3B isoform by adenovirus-mediated overexpression. In rat islets and rat insulinoma cells, approximate 10-fold overexpression of PDE3B was accompanied by a 6-8-fold increase in membrane-associated PDE3B activity. The cAMP concentration was significantly lowered in transduced cells (INS-1(832/13)), and insulin secretion in response to stimulation with high glucose (11.1 mm) was reduced by 40% (islets) and 50% (INS-1). Further, the ability of GLP-1 (100 nm) to augment glucose-stimulated insulin secretion was inhibited by approximately 30% (islets) and 70% (INS-1). Accordingly, when stimulating with cAMP, a substantial decrease (65%) in exocytotic capacity was demonstrated in patch-clamped single beta-cells. In untransduced insulinoma cells, application of the PDE3-selective inhibitor OPC3911 (10 microm) was shown to increase glucose-stimulated insulin release as well as cAMP-enhanced exocytosis. The findings suggest a significant role of PDE3B as an important regulator of insulin secretory processes.

Antidepressant-like profile and reduced sensitivity to rolipram in mice deficient in the PDE4D phosphodiesterase enzyme

Pharmacological inhibition of type 4 cyclic adenosine monophosphate (cAMP)-specific phosphodiesterase (PDE4) produces antidepressant-like effects in animals; however, it is not known which of the four PDE4 subtypes mediates these actions. In the present study, immunoblot analysis showed loss of phosphodiesterase 4D (PDE4D) expression in the cerebral cortex and hippocampus of PDE4D knockout (PDE4D-/-) mice, but unchanged PDE4A and PDE4B expression, relative to the wild type (PDE4D+/+) and heterozygous knockout (PDE4D+/-) mice. This reduced expression was accompanied by a reduction in PDE4 activity, while non-PDE4 activity was unchanged. PDE4D-/- mice exhibited decreased immobility in tail-suspension and forced-swim tests, which is indicative of an antidepressant-like effect on behavior. Desipramine and fluoxetine produced similar antidepressant-like effects in all three genotypes, even though their behavioral baselines differed markedly. By contrast, the PDE4 inhibitor rolipram only produced antidepressant-like effects in PDE4D+/+ mice. Consistent with this, rolipram potentiated isoproterenol-induced cyclic AMP formation only in the PDE4D+/+ mice. These results suggest that PDE4D is an essential mediator of the antidepressant-like effects of rolipram, and that PDE4D-regulated cyclic adenosine monophosphate signaling may play a role in the pathophysiology and pharmacotherapy of depression.

Differential distribution of PDE4D splice variant mRNAs in rat brain suggests association with specific pathways and presynaptical localization

cAMP plays an important role as a second-messenger molecule controlling multiple cellular processes. Its hydrolysis provides an important mechanism by which cAMP levels are regulated. This is performed by a large multigene family of cyclic nucleotide phosphodiesterases (PDEs). Members of the PDE4 enzyme family are selectively inhibited by rolipram. Five different mRNA splice forms for PDE4D have been isolated. Here, we analyzed the regional distribution of the mRNAs coding for the splice variants PDE4D1, PDE4D2, PDE4D3, PDE4D4, and PDE4D5 in the rat brain by in situ hybridization histochemistry using specific radiolabeled oligonucleotides. We found that all five splice variants showed a distinct distribution pattern and, in some cases, in association with specific brain pathways. The most relevant differences were in hippocampal formation, medial habenula, basal ganglia, and area postrema, at both the regional and cellular level. The dorsal and median raphe nuclei exclusively contained PDE4D2 mRNA transcripts, probably located on serotonergic cells. PDE4D1 mRNA was expressed in some white matter cells. PDE4D1 and PDE4D2 mRNA splice forms presented a similar distribution in the area postrema, whereas for PDE4D4 and PDE4D5 the cellular distribution presented a complementary pattern. The differential expression of PDE4D mRNA splice variants in the area postrema is consistent with their possible involvement in emesis control and suggests new molecular targets for a more selective drug design.

A novel cGMP signalling pathway mediating myosin phosphorylation and chemotaxis in Dictyostelium

Chemotactic stimulation of Dictyostelium cells results in a transient increase in cGMP levels, and transient phosphorylation of myosin II heavy and regulatory light chains. In Dictyostelium, two guanylyl cyclases and four candidate cGMP-binding proteins (GbpA- GbpD) are implicated in cGMP signalling. GbpA and GbpB are homologous proteins with a Zn2+-hydrolase domain. A double gbpA/gbpB gene disruption leads to a reduction of cGMP-phosphodiesterase activity and a 10-fold increase of basal and stimulated cGMP levels. Chemotaxis in gbpA(-)B(-) cells is associated with increased myosin II phosphorylation compared with wild-type cells; formation of lateral pseudopodia is suppressed resulting in enhanced chemotaxis. GbpC is homologous to GbpD, and contains Ras, MAPKKK and Ras-GEF domains. Inactivation of the gbp genes indicates that only GbpC harbours high affinity cGMP-binding activity. Myosin phosphorylation, assembly of myosin in the cytoskeleton as well as chemotaxis are severely impaired in mutants lacking GbpC and GbpD, or mutants lacking both guanylyl cyclases. Thus, a novel cGMP signalling cascade is critical for chemotaxis in Dictyostelium, and plays a major role in myosin II regulation during this process.

Identification of interaction sites of cyclic nucleotide phosphodiesterase type 3A with milrinone and cilostazol using molecular modeling and site-directed mutagenesis

To identify amino acid residues involved in PDE3-selective inhibitor binding, we selected eight presumed interacting residues in the substrate-binding pocket of PDE3A using a model created on basis of homology to the PDE4B crystal structure. We changed the residues to alanine using site-directed mutagenesis technique, expressed the mutants in a baculovirus/Sf9 cell system, and analyzed the kinetic characteristics of inhibition of the mutant enzymes by milrinone and cilostazol, specific inhibitors of PDE3. The mutants displayed differential sensitivity to the inhibitors. Mutants Y751A, D950A, and F1004A had reduced sensitivity to milrinone (K(i) changed from 0.66 microM for the recombinant PDE3A to 7.5 to 156 microM for the mutants), and diminished sensitivity to cilostazol (K(i) of the mutants were 18- to 371-fold higher than that of the recombinant PDE3A). In contrast, the mutants T844A, F972A and Q975A showed increased K(i) for cilostazol but no difference for milrinone from the recombinant PDE3A. Molecular models show that the PDE3 inhibitors cilostazol and milrinone share some of common residues but interact with distinct residues at the active site, suggesting that selective inhibitors can be designed with flexible size against PDE3 active site. Our study implies that highly conserved residuals Y751, D950 and F1004 in the PDE families are key residues for binding of both substrate and inhibitors, and nonconserved T844 may be responsible for the cilostazol selectivity of PDE3A. Detailed knowledge of the structure of inhibitory sites should contribute to development of more potent and specific inhibitory drugs.

Expression and role of phosphodiesterase 3 in human squamous cell carcinoma KB cells

Phosphodiesterase (PDE) 3s have been characterized in human squamous cell carcinoma KB cells. PDE3 activity was detected in homogenates of KB cells. PDE3A and 3B mRNAs were detected by RT-PCR in RNA from KB cells; the nucleotide sequences of the fragments were identical to those of human PDE3A and 3B. Immunoblotting with anti-PDE3 antibodies detected both PDE3A- and 3B-immunoreactive proteins in KB cells. The PDE3-specific inhibitor, cilostamide, inhibited the proliferation of KB cells. Our results indicate that PDE3s may be important regulators of the growth of KB cells. Therefore, PDE3 inhibitors may be potential new drugs for antiproliferative therapies in squamous cell carcinoma in the head and neck.