Abstract:Adenylyl cyclase (AC) converts ATP into cyclic AMP (cAMP), an important second messenger in cell signaling. Heterotrimeric G proteins and other regulators are important for control of AC activity. Depending on the AC isoform, Gbg subunits can either conditionally stimulate or inhibit cAMP synthesis. We previously showed that the Ga s -bg heterotrimer binds to the N terminus (NT) of type 5 AC (AC5). We now show that Gbg binds to the NT of a wide variety of AC isoforms. We hypothesized that Gbg/AC5 interactions … Show more
“…YFP-AC9 and Hsp20 display a significant signal by PLA as compared to YFP alone. Gβγ binds to the N-terminus of AC9 and serves as a positive control 21 .Figure 4AC9 association with Hsp20 is Yotiao independent. ( A ) Heart extracts from WT or AC9 −/− mice were subjected to IP with IgG (control) or anti-Hsp20.…”
Adenylyl cyclase type 9 (AC9) is found tightly associated with the scaffolding protein Yotiao and the IKs ion channel in heart. But apart from potential IKs regulation, physiological roles for AC9 are unknown. We show that loss of AC9 in mice reduces less than 3% of total AC activity in heart but eliminates Yotiao-associated AC activity. AC9−/− mice exhibit no structural abnormalities but show a significant bradycardia, consistent with AC9 expression in sinoatrial node. Global changes in PKA phosphorylation patterns are not altered in AC9−/− heart, however, basal phosphorylation of heat shock protein 20 (Hsp20) is significantly decreased. Hsp20 binds AC9 in a Yotiao-independent manner and deletion of AC9 decreases Hsp20-associated AC activity in heart. In addition, expression of catalytically inactive AC9 in neonatal cardiomyocytes decreases isoproterenol-stimulated Hsp20 phosphorylation, consistent with an AC9-Hsp20 complex. Phosphorylation of Hsp20 occurs largely in ventricles and is vital for the cardioprotective effects of Hsp20. Decreased Hsp20 phosphorylation suggests a potential baseline ventricular defect for AC9−/−. Doppler echocardiography of AC9−/− displays a decrease in the early ventricular filling velocity and ventricular filling ratio (E/A), indicative of grade 1 diastolic dysfunction and emphasizing the importance of local cAMP production in the context of macromolecular complexes.
“…YFP-AC9 and Hsp20 display a significant signal by PLA as compared to YFP alone. Gβγ binds to the N-terminus of AC9 and serves as a positive control 21 .Figure 4AC9 association with Hsp20 is Yotiao independent. ( A ) Heart extracts from WT or AC9 −/− mice were subjected to IP with IgG (control) or anti-Hsp20.…”
Adenylyl cyclase type 9 (AC9) is found tightly associated with the scaffolding protein Yotiao and the IKs ion channel in heart. But apart from potential IKs regulation, physiological roles for AC9 are unknown. We show that loss of AC9 in mice reduces less than 3% of total AC activity in heart but eliminates Yotiao-associated AC activity. AC9−/− mice exhibit no structural abnormalities but show a significant bradycardia, consistent with AC9 expression in sinoatrial node. Global changes in PKA phosphorylation patterns are not altered in AC9−/− heart, however, basal phosphorylation of heat shock protein 20 (Hsp20) is significantly decreased. Hsp20 binds AC9 in a Yotiao-independent manner and deletion of AC9 decreases Hsp20-associated AC activity in heart. In addition, expression of catalytically inactive AC9 in neonatal cardiomyocytes decreases isoproterenol-stimulated Hsp20 phosphorylation, consistent with an AC9-Hsp20 complex. Phosphorylation of Hsp20 occurs largely in ventricles and is vital for the cardioprotective effects of Hsp20. Decreased Hsp20 phosphorylation suggests a potential baseline ventricular defect for AC9−/−. Doppler echocardiography of AC9−/− displays a decrease in the early ventricular filling velocity and ventricular filling ratio (E/A), indicative of grade 1 diastolic dysfunction and emphasizing the importance of local cAMP production in the context of macromolecular complexes.
“…42 This regulation is also dependent upon the isoform specificity of types of Gβ and Gγ, adding to the complexity of the mechanism. 43 Besides affecting cAMP levels, Gβγ has other effects on membrane ion channels that influence the electrophysiological properties.…”
Objective: Much evidence suggests that the subiculum plays a significant role in the regulation of epileptic activity. Lactate acts as a neuroprotective agent against many conditions that cause brain damage. During epileptic seizures, lactate formation reaches up to ~6 mmol/L in the brain. We investigated the effect of lactate on subicular pyramidal neurons after induction of epileptiform activity using 4-aminopyridine (4-AP-0Mg 2+ ) in an in vitro epilepsy model in rats. The signaling mechanism associated with the suppression of epileptiform discharges by lactate was also investigated. Methods: We used patch clamp electrophysiology recordings on rat subicular neurons of acute hippocampal slices. Immunohistochemistry was used for demonstrating the expression of hydroxycarboxylic acid receptor 1 (HCA1) in the subiculum. Results: Our study showed that application of 6 mmol/L lactate after induction of epileptiform activity reduced spike frequency (control 2.5 ± 1.23 Hz vs lactate 1.01 ± 0.91 Hz, P = .049) and hyperpolarized the subicular neurons (control −51.8 ± 1.9 mV vs lactate −57.2 ± 3.56 mV, P = .002) in whole cell patch-clamp experiments. After confirming the expression of HCA1 in subicular neurons, we demonstrated that lactate-mediated effect occurs via HCA1 by using its specific agonist. All values are mean ±SD. Electrophysiological recordings revealed the involvement of Gβγ and intracellular cAMP in the lactate-induced effect. Furthermore, current-clamp and voltage-clamp experiments showed that the G protein-coupled inwardly rectifying potassium (GIRK) channel blocker tertiapin-Q, negated the lactateinduced inhibitory effect, which confirmed that lactate application results in outward GIRK current. Significance: Our finding points toward the potential role of lactate as an anticonvulsant by showing lactate-induced suppression of epileptiform activity in subicular neurons. The study gives a different insight by suggesting importance of endogenous metabolite and associated signaling factors, which can aid in improving the present therapeutic approach for treating epilepsy.
“…Gβγ is reported to enhance Gsα or forskolin-stimulated activities of mACs 2, 4, 5, 6, and 7, but to have no effect alone (reviewed in (Brand, Sadana et al, 2015, Willoughby & Cooper, 2007). On the other hand, Gβγ inhibits mACs 1, 3, and 8, and is even reported to inhibit AC5 and 6 (Steiner, Avidor-Reiss et al, 2005, Tesmer & Sprang, 1998, Willoughby & Cooper, 2007.…”
Mammalian adenylate cyclases (ACs) are pseudoheterodimers with dissimilar hexahelical membrane-anchors, isoform-specifically conserved for more than half a billion years. We exchanged both membrane anchors of the AC isoform 2 by the isosteric quorum-sensing receptor from Vibrio, CqsS, which has a ligand, Cholera-Autoinducer-1 (CAI-1). In the chimera, AC activity was stimulated by Gsα, CAI-1 had no effect. Surprisingly, CAI-1 inhibited Gsα stimulation. We report that Gsα stimulation of human AC isoforms 2, 3, 5, and 9 expressed in Sf9 cells is inhibited by serum as is AC activity in membranes from rat brain cortex. AC2 activation by forskolin or forskolin/Gsα was similarly inhibited. Obviously, serum contains as yet unidentified factors affecting AC activity. The data establish a linkage in ACs, in which the membrane anchors, as receptors, transduce extracellular signals to the cytosolic catalytic dimer. A mechanistic three state model of AC regulation is presented compatible with all known regulatory inputs into mammalian ACs. The data allow designating the membrane anchors of mammalian ACs as orphan receptors and establish a new level of AC regulation. keywords: adenylate cyclases / cyclic AMP / membrane anchor / quorum-sensor / receptor
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