Search

We have cloned and characterized the first human isozyme in a new family of cyclic nucleotide phosphodiesterases, PDE9A. By sequence homology in the catalytic domain, PDE9A is almost equidistant from all eight known mammalian PDE families but is most similar to PDE8A (34% amino acid identity) and least like PDE5A (28% amino acid identity). We report the cloning of human cDNA encoding a full-length protein of 593 amino acids, including a 261-amino acid region located near the C terminus that is homologous to the approximately 270-amino acid catalytic domain of other PDEs. PDE9A is expressed in all eight tissues examined as a approximately 2. 0-kilobase mRNA, with highest levels in spleen, small intestine, and brain. The full-length PDE9A was expressed in baculovirus fused to an N-terminal 9-amino acid FLAG tag. Kinetic analysis of the baculovirus-expressed enzyme shows it to be a very high affinity cGMP-specific PDE with a Km of 170 nM for cGMP and 230 microM for cAMP. The Km for cGMP makes PDE9A one of the highest affinity PDEs known. The Vmax for cGMP (4.9 nmol/min/microg recombinant enzyme) is about twice as fast as that of PDE4 for cAMP. The enzyme is about twice as active in vitro in 1-10 mM Mn2+ than in the same concentration of Mg2+ or Ca2+. PDE9A is insensitive (up to 100 microM) to a variety of PDE inhibitors including rolipram, vinpocetine, SKF-94120, dipyridamole, and 3-isobutyl-1-methyl-xanthine but is inhibited (IC50 = 35 microM) by zaprinast, a PDE5 inhibitor. PDE9A lacks a region homologous to the allosteric cGMP-binding regulatory regions found in the cGMP-binding PDEs: PDE2, PDE5, and PDE6.

As part of our efforts to understand the regulation of intracellular cAMP and to generate new targets for pharmacological intervention, we have cloned and characterized the first isozyme in a new family of cyclic nucleotide phosphodiesterases, PDE8A. PDE8A is most similar to PDE4 (38.5% amino acid identity in the catalytic domain), but is clearly not a member of any of the seven known PDE families. We report the cloning of human cDNA encoding the C-terminal 713 amino acids of the protein, including a 283 amino acid region located near the C-terminus that is homologous to the approximately 270 amino acid catalytic domain of other PDEs. In addition, we found cDNA sequences consistent with alternative 5' mRNA splicing analogous to that seen in other PDE genes. PDE8A is expressed in a wide variety of tissues as a approximately 4.5 kb mRNA, with highest levels in testis, ovary, small intestine, and colon. The C-terminal 545 amino acids of PDE8A (the region shared among all splice variants) were expressed in baculovirus. Kinetic analysis of the baculovirus expressed enzyme shows it to be a very high affinity cAMP specific PDE with a Km of 55 nM for cAMP and 124 microM for cGMP. The Vmax (150 pmol/min/microgram recombinant enzyme) is about 10 times slower than that of PDE4. The cAMP hydrolytic activity of PDE8A is not modulated by cGMP at concentrations up to 100 microM. The enzyme requires the presence of at least 1 mM Mn2+ or Mg2+ for maximal activity in vitro, while 100 mM Ca2+ restores only about 20% activity. PDE8A is insensitive (up to 100 microM) to a variety of PDE inhibitors including rolipram, zaprinast, vinpocetine, SKF-94120, and IBMX, but is inhibited (IC50 = 9 microM) by the PDE inhibitor dipyridimole. To give PDE8A a descriptive name that distinguishes it from the other two known high affinity cAMP-specific phosphodiesterases (PDE4 and PDE7), we denote PDE8A as the high affinity cAMP-specific and IBMX-insensitive PDE.

Hepatic cholesterol 7 alpha-hydroxylase (CH-7 alpha) activity in intact rats depleted of glutathione (GSH) was reduced significantly (P < 0.007) compared with that in untreated controls. Northern blot analysis of poly A+ mRNA isolated from GSH-depleted and control rat livers showed that there was a reduction in mRNA for CH-7 alpha in treated rats that was commensurate with the reduction in CH-7 alpha activity. The fact that the level of transferrin mRNA was unaltered by the depletion of GSH suggests that the change in steady-state CH-7 alpha mRNA content is specifically sensitive to GSH content. This observation extends previous in vitro findings and provides strong justification for a more detailed biochemical investigation into the interaction between GSH levels and the regulation of CH-7 alpha mRNA levels.

Assay procedures for determining serum haptoglobin concentration and ceruloplasmin oxidase activity in dogs were validated, and reference values were established. Serum haptoglobin concentration is reported as milligrams per deciliter of cyanmethemoglobin binding capacity, whereas serum ceruloplasmin oxidase activity was determined by use of p-phenylenediamine as substrate. Both assays were used to analyze serum samples from 288 dogs. In each dog's case record, clinical history and final diagnosis were evaluated to determine whether the dog had an inflammatory condition. Complete blood cell counts were performed in 265 dogs, using simultaneously collected blood samples. Plasma fibrinogen concentration was determined for 161 dogs. A positive correlation (P less than 0.01) for serum haptoglobin concentration and for ceruloplasmin oxidase activity, compared with WBC counts, segmented neutrophil and band neutrophil counts, and plasma fibrinogen concentration. Ceruloplasmin oxidase activity and haptoglobin concentration were up to 6 times more sensitive than fibrinogen concentration or leukocyte counts in detecting inflammation. Specificity of ceruloplasmin oxidase activity was comparable to fibrinogen concentration and leukocyte counts, whereas haptoglobin concentration was found to be slightly less specific. Specificity of haptoglobin concentration improved slightly (from 0.82 to 0.88) when dogs with a history of glucocorticoid administration were excluded from analysis. Predictive value of a negative test result (haptoglobin concentration less than 125 mg/dl; ceruloplasmin oxidase activity less than 20 IU/L) and predictive value of a positive test result for haptoglobin concentration and ceruloplasmin activity were comparable to or better than fibrinogen concentration or various oxidase leukocyte counts in detection of inflammation in a variety of disease conditions.(ABSTRACT TRUNCATED AT 250 WORDS)