Molecular signal transduction of cAMP compartments

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A large number of G protein coupled receptors (GPCR) utilize cAMP as their second messenger to induce alterations in cell function. In fact, in the same cell several different GPCR can increase cAMP, leading to the question of how the cell interprets the signals from these receptors differently. The concept of cAMP compartmentation, where the second messenger is not generated uniformly throughout the cell, is readily accepted yet poorly understood. We have found that the enzymes that synthesize cAMP, adenylyl cyclases (AC's), are not uniformly distributed through the plasma membrane. Furthermore, GPCR can preferentially couple to certain AC isoforms due to colocalization in lipid rafts. While we have made progress in understanding how specific receptors can couple to certain AC's, little progress has been made in defining the compartments of cAMP inside cells and even less is known about what cellular responses can be modified by different pools of cAMP. One problem has been that common cell models used in the field lack highly compartmentized cAMP pools. We have found that cultured human airway smooth muscle (HASM) cells express identifiable cAMP compartments. Furthermore, we can define these compartments based on the isoforms of AC they express. We have observed that signaling by cAMP generated by AC2, but not AC6 or other AC's, leads to the expression of IL-6 by HASM. Moreover, cAMP generated by AC6, but not by AC2, increases expression of somatostatin and stimulates a cell shape change called arborization. Thus, AC2- and AC6-specific responses can be used to define the cAMP signaling compartments in HASM. The goal of this project is to characterize the other components of these two cAMP compartments by using overexpression and knockdown of specific AKAP's and PDE's. Novel AC mutants will be used to manipulate AC localization and function to determine how these pools are assembled. This project proposes novel, multidisciplinary approaches to define the components responsible for establishing and maintaining cAMP signaling compartments. Results will have broad applicability due to the fundamental nature of cAMP signaling, but because a well-differentiated cell model is used, our findings will also have direct relevance to asthma and COPD therapy. GM107094 Ostrom, Rennolds S 2.