Mechanisms of cyclic GMP mediation of hormone action
The naturally occurring cyclic nucleotide, cyclic GMP, mediates the effects of hormones, neurotransmitters, and other agents on many biological processes. Blood flow, blood pressure, nerve transmission, airway distension, and penile erection are but a few such processes. Our research concerns the mechanisms by which cyclic GMP causes these effects. The focus is on two classes of enzymes known to be receptors for cyclic GMP: (1) cyclic GMP-dependent protein kinases and (2) phosphodiesterases.
Studies include incubation of intact cells (coronary artery strips, aorta cells) with hormones, neurotransmitters, and cyclic nucleotide analogs followed by measurements of the physiological responses. The investigations also include identification and purification of isozymic forms, cloning of their cDNAs, and studies of enzyme and regulatory mechanisms by biochemical and molecular biological methods. Changes in the conformations of these proteins caused by cyclic nucleotide binding and phosphorylation are being measured.
Of particular interest are the mechanisms by which cyclic nucleotides bind to the enzymes and stimulate protein phosphorylation or other processes. Deletion mutagenesis and site-directed mutagenesis are being used to identify important structural elements in the regulatory components of these enzymes. The physiological substrates for cyclic GMP-dependent protein kinases are being identified and autophosphorylation of the protein kinases is being examined.
The negative feedback regulation of cellular cyclic nucleotide levels is being studied. A probable target of negative feedback, a cyclic GMP-binding phosphodiesterase, which was discovered in this laboratory, is being characterized, and the probability that this enzyme is modulated by both allosteric regulation and protein phosphorylation is being examined. A possible role for zinc in the catalytic mechanism of the phosphodiesterase is being studied. This phosphodiesterase, also referred to as PDE5, is the site of action of the new male impotence drug Viagra, which causes penile erection.