Cyclic AMP functions as the chemotactic signal during aggregation of single-celled amoebae of the cellular slime mold Dictyostelium discoideum. Evidence suggests that cyclic AMP also acts as a regulatory molecule during Dictyostelium multicellular differentiation. Biochemical characterization of adenylate cyclase, the cyclic AMP synthetic enzyme, was accomplished using a sensitive radioimmunoassay. The enzyme was found to be pellet-bound. The non-ionic detergents, Triton X-100 and Lubrol PX, were not effective for solubilizing this activity. Magnesium or manganese could serve as the required divalent cation, with the Mn-supported activity over 4-fold greater than the Mg-supported activity. Typical mammalian adenylate cyclase modulators such as guanyl nucleotides, fluoride, and cholera toxin did not activate the Dictyostelium enzyme. Calcium, in conjunction with its protein receptor calmodulin, did not appear to regulate the enzyme. An endogenous extracellular, heat-stable substance was found to inhibit Dictyostelium adenylate cyclase. By use of ultramicrotechniques adenylate cyclase activity was localized in the pre-spore cells of the culminating individual with no activity detected in the pre-stalk region. Lack of detectable activity in the pre-stalk cells may be due to a masking by the endogenous inhibitor. An increasing gradient of activity was found in the pre-spore mass with activity increasing from the uppermost area to the base. No striking localization was seen prior to the pre-culmination stage of development. Two peaks in cyclic AMP levels, as measured in individuals were found during development. One coincided with aggregation, the other occurred at the culmination stage. A gradient of cyclic AMP within the culminating individual paralleled the gradient of adenylate cyclase activity. The tip of the individual had greater levels of cyclic AMP than the middle pre-spore region, and the upper stalks had higher levels than the lower stalks. These data indicate an enzymatic potential for establishing a gradient of cyclic AMP. At the culmination stage of development this molecule could act to direct the chemotactic movements of the pre-stalk cells as well as provide positional information for the terminal differentiation of the pre-spore cells into mature spores. / Ph. D.

Surgical intervention can result in endothelial denudation, driving growth factor-stimulated vascular smooth muscle cell (VSMC) migration towards the intima, leading to luminal narrowing and restenosis. Clinically approved PGI₂ analogues, including beraprost, activate the cyclic adenosine monophosphate (cAMP) signaling pathway to inhibit VSMC migration in vitro. This pathway is a potential therapeutic target, however the downstream proteins involved in the inhibitory effects of cAMP on migration remain unknown. The aims of this study were to determine the signalling pathways involved in inhibiting VSMC migration through cAMP downstream mediators, protein kinase A (PKA) and the more recently characterised exchange protein activated by cAMP (Epac), and delineate the mechanisms involved. In human saphenous vein VSMCs, Epac activation using an Epac analogue inhibited VSMC migration. Therapeutic concentrations of beraprost (1 nM) also resulted in an inhibition of VSMC migration. The use of fluorescence resonance energy transfer (FRET) confirmed 1 nM beraprost activated Epac, but not PKA. Epac is a guanine nucleotide exchange factor (GEF) for Rap1 thus Rap1 siRNA was used to inhibit the Epac pathway. This blocked the inhibitory effects of beraprost on VSMC migration. Epac1 was localised to the leading edge of migrating VSMCs. Another G-protein, RhoA, was investigated since it is essential for cell migration and is involved in several processes including actin regulation. Epac signaling inhibited PDGF-induced RhoA activation and disassembled F-actin at the leading edge, where Epac1 was previously located. This indicates that beraprost activated the Epac pathway, which inhibited RhoA to decrease VSMC migration. The clinical relevance of this study has discovered the mechanisms of Epac's inhibitory action on VSMC migration and this pathway could be targeted therapeutically to reduce restenosis. In the future the potential use of beraprost on a drug eluting stent might be beneficial to prevent restenosis formation following surgical intervention.

published_or_final_version / Anatomy / Master / Master of Philosophy

Two separate experiments were designed to measure urinary cyclic AMP and renal papillary cyclic AMP, respectively, Results suggest that urinary cyclic AMP excretion rate is unchanged and cannot be used as an index of tubular sensitivity to either vasopressin or fluoride. However, renal papillary tissue cyclic AMP increased significantly (p<0.05) at plasma fluoride concentrations which result in polyuric renal failure. Further, it appears that fluoride independently stimulates cyclic AMP in the papilla, demonstrated by the additive effect with vasopressin. It was postulated that the defect in water reabsorption induced by fluoride must be at a step subsequent to the generation of cyclic AMP, because one would expect to see an antidiuresis, not a diuresis with increased tissue cyclic AMP.

Thesis (Ph. D.)--University of Missouri--Columbia, 2001. / "May 2001." Typescript. Vita. Includes bibliographical references (leaves 88-99). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri--Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 88-99). Also available on the Internet.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1975. / Bibliography: leaves 98-104.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 144-163) Also available in print.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 110-127).

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 144-163) Also available online.