In disorders such as Sjogrens syndrome the regulation of secretory proteins is impaired. Thus, a major research goal of this laboratory is to elucidate the mechanisms involved in the regulation of protein secretion. In particular, emphasis is placed on cAMP-stimulated secretion. Cyclic AMP microdomains are shaped by adenylyl cyclases that form cAMP as well as phosphodiesterases that degrade cAMP. For years it was believed that cAMP produced its effects solely through the cAMP-protein kinase A (PKA) pathway. However, newly discovered Epac, a guanine nucleotide exchange factor that belongs to the cAMP-binding protein family, also exerts diverse effects on cellular functions, including hormone-induced secretion from parotid acinar cells. The discovery of Epac has added a new dimension to the cAMP field. Thus, cAMP can regulate intracellular events including the modulation of amylase release by coordinating both cAMP/PKA-dependent and cAMP/PKA-independent mechanisms. To date, little is known about the mechanisms by which both PKA and Epac regulate secretion. Cells are no longer thought of as bags of enzymes. Instead a picture of highly organized cellular architecture with tightly coordinated signaling complexes is emerging. A key component to this coordination is the organization of multiple signaling enzymes and scaffolding proteins into discrete signal transduction organizing complexes. Recent studies indicate that A-kinase anchoring proteins (AKAPs) target PKA to specific substrates and distinct subcellular compartments providing spatial and temporal specificity for mediation of biological effects. Although much less is known about the mechanisms involved in Epac regulated amylase release, Epac is known to activate Rap1, a small GTP-binding protein that my laboratory reported to be associated with secretion from parotid cells. Thus, a goal of my laboratory is to determine effectors involved in Epac-stimulated amylase release and their contribution to amylase release.

Regulation of calcium/cAMP signaling and secretion by serine/threonine phosphatases.

The coordination of kinase and serine/threonine phosphatase activities provides for a rapid onset of physiological responses that increase cellular responses elicited by hormones. Although serine/threonine phosphatases have been shown to regulate calcium release and entry, and more recently, cAMP metabolism and secretion, little attention has been given to understanding the mechanisms involved. Importantly, their localization in cells determines their targets and function. It is now known that serine/threonine phosphatases are part of signaling complexes made up of kinases, phosphodiestereases, intracellular calcium receptors, and the cytoskelton. My laboratory is interested in identifying and determining the localization of serine/threonine phosphatases within signaling complexes in salivary cells, and the mechanism(s) by which these complexes regulate cellular processes.