Many hormones, drugs and other agents modify physiological processes by causing changes in cAMP and cGMP. The amplitude and duration of these second messenger signals are controlled in large part by the activity of the specific cyclic nucleotide phosphodiesterases (PDEs) that control their degradation. The signaling pathways regulated by PDEs include such well known processes as visual transduction and male erectile function. They also include less well known pathways such as regulation of aldosterone by atrial natriuretic peptide and regulation of platelet aggregation by endothelial relaxation factor. Drugs that selectively inhibit individual PDE isozymes have a wide variety of different effects on an animals suggesting specific roles for most of the different PDEs.
Current evidence indicates that there are eleven related but unique gene families that code for different PDEs and that most of these families contain more than one gene. Furthermore, each gene product is differentially spliced in different tissues to yield different isozymes. A major focus of this laboratory has been to determine the molecular nature for the normal control of these isoenzymes. Many of the current projects involve approaches to determine which cell types contain what isozyme, and how that particular isozyme contributes to the phenotype of the cell. In addition, recent advances in the crystal structure of several of these isozymes has allowed series of structure/function studies to be initiated. Finally, several of these isozymes are regulated by covalent modification. Studies are underway to determine how and to what extent these types of regulation are important to the physiological functions of the cells in which the PDEs are expressed.
A wide variety of experimental approaches are employed. They vary from basic in vitro enzymological studies with extracts of tissues to refined x-ray crystallography and protein chemistry approaches using pure proteins obtained from over expressing the individual PDE cDNAs. Similarly, in vivo approaches utilizing transgenic animals allow function at the whole animal level to be investigated. This includes recent methods of inducible siRNA and FRET visualization of cyclic nucleotide levels. In all cases, emphasis is placed on how and why each isozyme functions as it does in a tissue. Currently projects on the roles of the PDEs in such diverse processes as synaptic plasticity, control of insulin secretion, monocyte, macrophage and dendritic cell maturation, control of T-cell function and regulation of smooth muscle proliferation are being carried out.