Human cGMP-stimulated cyclic nucleotide phosphodiesterase

Details Human cGMP-stimulated cyclic nucleotide phosphodiesterase Human cGMP-stimulated cyclic nucleotide phosphodiesterase

2001-06-18

2003-11-04

Slobodyansky, Elizabeth (Department: 1652)

Chemistry: molecular biology and microbiology

Enzyme , proenzyme; compositions thereof; process for...

Hydrolase

C536S023200

Reexamination Certificate

active

06642040

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to novel purified and isolated nucleotide sequences encoding mammalian Ca
2+
/calmodulin stimulated phosphodiesterases (CaM-PDEs) and cyclic-GMP-stimulated phosphodiesterases (cGS-PDEs). Also provided are the corresponding recombinant expression products of said nucleotide sequences, immunological reagents specifically reactive therewith, and procedures for identifying compounds which modulate the enzymatic activity of such expression products.
Cyclic nucleotides are known to mediate a wide variety of cellular responses to biological stimuli. The cyclic nucleotide phosphodiesterases (PDEs) catalyze the hydrolysis of 3′, 5′ cyclic nucleotides, such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), to their corresponding 5′-nucleotide monophosphates and are consequently important in the control of cellular concentration of cyclic nucleotides. The PDEs in turn are regulated by transmembrane signals or second messenger ligands such as calcium ion (Ca
2+
) or cGMP. The PDEs thus have a central role in regulating the flow of information from extracellular hormones, neurotransmitters, or other signals that use the cyclic nucleotides as messengers.
PDEs are a large and complex group of enzymes. They are widely distributed throughout the cells and tissues of most eukaryotic organisms, but are usually present only in trace amounts. At least five different families of PDEs have been described based on characteristics such as substrate specificity, kinetic properties, cellular regulatory control, size, and in some instances, modulation by selective inhibitors. [Beavo,
Adv. in Second Mess. and Prot. Phosph. Res.
22:1-38 (1988)]. The five families include:
I
Ca
2+
/calmodulin-stimulated
II
cGMP-stimulated
III
cGMP-inhibited
IV
cAMP-specific
V
cGMP-specific
Within each family there are multiple forms of closely related PDES. See Beavo, “Multiple Phosphodiesterase Isozymes Background, Nomenclature and Implications”, pp. 3-15; Wang et al., “Calmodulin-Stimulated Cyclic Nucleotide Phosphodiesterases”, pp. 19-59; and Manganiello et al., “Cyclic GMP-Stimulated Cyclic Nucleotide Phosphodiesterases” pp. 62-85; all in
Cyclic Nucleotide Phosphodiesterases: Structure, Regulation and Drug Action
, Beavo, J. and Houslay, M. D., Eds.; John Wiley & Sons, New York (1990).
The Ca
2+
/calmodulin dependent PDEs (CaM-PDEs) are characterized by their responsiveness to intracellular calcium, which leads to a decreased intracellular concentration of cAMP and/or cGMP. A distinctive feature of cGMP-stimulated phosphodiesterases (cGS-PDEs) is their capacity to be stimulated by cGMP in effecting cAMP hydrolysis.
In vitro studies have shown increased PDE activity in response to Ca
2+
/calmodulin in nearly every mammalian tissue studied, as well as in Drosophila, Dictyostelium, and trypanosomes. The level of CaM-PDE in tissues and cellular and subcellular compartments varies widely. Most cells contain at least a small amount of CaM-PDE activity, with the highest tissue levels being found in the brain, particularly in the synaptic areas. Greenberg et al.
Neuropharmacol.,
17:737-745 (1978) and Kincaid et al.,
PNAS (USA),
84:1118-1122 (1987). A decrease in cAMP in astrocytoma cells in response to muscarinic stimulation may be due to calcium dependent increases in CaM-PDE activity. Tanner et al.,
Mol. Pharmacol.,
29:455-460 (1986). Also, CaM-PDE may be an important regulator of cAMP in thyroid tissue. Erneux et al.,
Mol. Cell. Endocrinol.,
43:123-134(1985).
Early studies suggested that there are distinct tissue-specific isozymes of CaM-PDEs. Several members of the CaM-PDE family have now been described, including a 59 kDa isozyme isolated from bovine heart, and 61 and 63 kDa isozymes isolated from bovine brain. LaPorte et al.,
Biochemistry,
18:2820-2825 (1979); Hansen et al.,
Proc. Natl. Acad. Sci. USA,
79:2788-2792 (1982); and Sharma et al.,
J. Biol. Chem.,
261:14160-14166 (1986). Possible counterparts to the bovine 59 and 61 kDa isozymes have also been isolated from rat tissues, Hansen et al.,
J. Biol. Chem.,
261:14636-14645 (1986), suggesting that these two isozymes may be expressed in other mammalian species.
In addition to molecular weight criteria, other evidence supports both similarities and differences among the CaM-PDE family of isozymes. For example, the 59 kDa heart isozyme and the 61 kDa brain isozyme CaM-PDEs differ in mobility on SDS-PAGE and elution position on DEAE chromatography, and the 59 kDa isozyme has at least a 10-20 fold higher affinity for calmodulin. Oncomodulin, a fetal/onco calcium binding protein present in very high concentrations in the placenta and transformed cells, also binds to the 59 kDa enzyme with a higher affinity than to the 61 kDa enzyme. However, both the 61 kDa brain and the 59 kDa heart isozymes are recognized by a single monoclonal antibody. This antibody binds to the Ca
2+
/CaM-PDE complex with 100-fold higher affinity than to PDE alone. Hansen et al., 1986, supra. The 59 and 61 kDA isozymes have nearly identical substrate specificities and kinetic constants. Krinks et al.,
Adv. Cyc. Nucleotide Prot. Phosphorylation Res.,
16:31-47 (1984) have suggested, based on peptide mapping experiments, that the heart 59 kDa protein could be a proteolytic form of the brain 61 kDa isozyme.
The 63 kDa bovine brain isozyme differs substantially from the 59 and 61 kDa isozymes. The 63 kDa enzyme is not recognized by the monoclonal antibody which binds to the 59 and 61 kDa enzymes. Hansen et al., 1986, supra. The 63 kDa protein is not phosphorylated in vitro by cAMP-dependent protein kinase, whereas the 61 kDa protein is phosphorylated. Further, only the 63 kDa protein is phosphorylated in vitro by CaM-kinase II. Sharma et al.,
Proc. Natl. Acad. Sci. (USA),
82:2603-2607 (1985); and Hashimoto et al., J. Biol. Chem., 264:10884-10887 (1989). The 61 and 63 kDa CaM-PDE isozymes from bovine brain do appear, however, to have similar CaM-binding affinities. Peptide maps generated by limited proteolysis with Staphylococcal V8 protease, Sharma et al.,
J. Biol. Chem.,
259:9248 (1984), have suggested that the 61 and 63 kDa proteins have different amino acid sequences.
The cGMP-stimulated PDEs (cGS-PDEs) are proposed to have a noncatalytic, cGMP-specific site that may account for the stimulation of cAMP hydrolysis by cGMP. Stoop et al.,
J. Biol. Chem.,
264:13718 (1989). At physiological cyclic nucleotide concentrations, this enzyme responds to elevated cGMP concentrations with an enhanced hydrolysis of cAMP. Thus, cGS-PDE allows for increases in cGMP concentration to moderate or inhibit cAMP-mediated responses. The primary sequence presented recently in LeTrong et al.,
Biochemistry,
29:10280 (1990), co-authored by the inventors herein, provides the molecular framework for understanding the regulatory properties and domain substructure of this enzyme and for comparing it with other PDE isozymes that respond to different signals. This publication also notes the cloning of a 2.2 kb bovine adrenal cortex cDNA fragment encoding cGS-PDE. See also, Thompson et al.,
FASEB J.,
5(6):A1592 (Abstract No. 7092) reporting on the cloning of a “Type II PDE” from rat pheochromocytoma cells.
With the discovery of the large number of different PDEs and their critical role in intracellular signalling, efforts have focused on finding agents that selectively activate or inhibit specific PDE isozymes. Agents which affect cellular PDE activity, and thus alter cellular cAMP, can potentially be used to control a broad range of diseases and physiological conditions. Some drugs which raise cAMP levels by inhibiting PDEs are in use, but generally act as broad nonspecific inhibitors and have deleterious side effects on cAMP activity in nontargeted tissues and cell types. Accordingly, agents are needed which are specific for selected PDE isozymes. Selective inhibitors of specific PDE isozymes may be useful as cardiotonic agents, anti-depressants, anti-hyperte

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