The Type 8 Adenylyl Cyclase Is Critical for Ca2+Stimulation of cAMP Accumulation in Mouse Parotid Acini

Abstract

2؉ , independently of CaM, inhibited isoproterenol-stimulated AC. Data suggest that agonist augmentation of stimulated cAMP levels is due to activation of AC8 in mouse parotid acini, and strongly support a role for AC5/6 in the inhibition of stimulated cAMP levels.To date, 10 different ACs, 1 each with distinct regulatory properties, have been cloned; their existence suggests that they may be differentially regulated. The enzymes exhibit type specific stimulatory and inhibitory regulation by G-protein ␣ and ␤␥ subunits, Ca 2ϩ , CaM, forskolin, P-site inhibitors, protein kinases A and C (PKC) (2-6), and calcineurin (7) entry plays an important role in promoting AC synthesis. These data, combined with findings that AC8 is expressed in mouse parotid acini (1) and that Ca 2ϩ /CaM stimulates AC and augments the effects of forskolin on cyclase activity in membrane fractions and intact cells (21,22), are consistent with results obtained in HEK 293 cells expressing AC8 (8, 11).Interpretation of the mechanism(s) involved in the cross-talk that occurs between the Ca 2ϩ and cAMP signaling pathways in cells is complex and requires not only identification of AC subtypes expressed, but also tools that provide definitive answers as to regulation of AC synthesis in specific cell types. Thus, the goal of the present study was to determine the involvement of AC8 in agonist-induced augmentation of stimulated cAMP levels in mouse parotid acini by examining the effects of carbachol and the microsomal Ca 2ϩ -ATPase inhibitor, thapsigargin, on isoproterenol-induced cAMP accumulation in acini from AC8-KO mice. Our data show that carbachol and thapsigargin augmented stimulated cAMP accumulation in acini from wild type (WT) mice as previously reported (1), whereas these agents not only prevented augmentation, but inhibited isoproterenol-induced cAMP accumulation in AC8-KO mice. Augmentation of stimulated cAMP accumulation, however, was not affected in acini from AC1-KO mice. Agonist-induced inhibition of stimulated cAMP accumulation was reversed in a nominally Ca 2ϩ -free buffer and in the presence of lanthanum (La 3ϩ ), but not by KN-62, an inhibitor of CaM kinase, or by the CaM antagonist, calmidazolium. Studies with isolated parotid membranes revealed that Ca 2ϩ , independently of CaM, inhibits AC activity in a concentration-dependent manner, consistent with the expression of the Ca 2ϩ -inhibited AC5/6 isoforms in parotid gland. Results demonstrate that capacitative Ca 2ϩ entry is associated with the activation of AC8 in mouse parotid acini and support an involvement of AC5/6 in the inhibition of cAMP synthesis.

Type VIII adenylyl cyclase in rat beta cells: coincidence signal detector/generator for glucose and GLP-1

“…Co-localisation of Ca 2+ -sensitive AC and capacitative Ca 2+ -entry channels was found in embryonic kidney cells [62,63], as well as in cardiac myocytes [64] and in parotid cells [65]. It will be a challenge for future studies to study such co-localisation in beta cells, since this spatial organization may contribute to foci of cellular cAMP formation when cells are exposed to hormone as observed in other cell types [66,67].…”

α-1 adrenergic receptor agonists modulate ductal secretion of BDL rats via Ca2+- and PKC-dependent stimulation of cAMP

“…In other cells, adenylyl cyclase isoforms 5 and 6 are inhibited by Ca 2ϩ agonists through a calmodulin-independent mechanism, which leads to decreased cAMP release. 45,46 In summary, cholangiocyte secretion is positively modulated by the cholinergic system via acetylcholine M3 receptors 5,9 and the adrenergic system via ␣-1 adrenergic receptor agonists. However, although acetylcholine positively modulates adenylate cyclase through Ca 2ϩ and calmodulin-dependent but PKC-insensitive Phenylephrine did not alter PKA activity.…”

Why Calcium-Stimulated Adenylyl Cyclases?

“…AC8 is expressed in brain, lung (19), and parotid gland (36) (43), suggesting that interaction with CaM in this region is required for maximal AC1 activation. AC1 is not stimulated by G s -coupled receptors alone.…”