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Selective coupling of type 6 adenylyl cyclase with type 2 IP3 receptors mediates direct sensitization of IP3 receptors by cAMP.

Tovey SC, Dedos SG, Taylor EJ, Church JE, Taylor CW - J. Cell Biol. (2008)

Bottom Line: Human embryonic kidney cells express several isoforms of adenylyl cyclase (AC) and IP(3)R, but IP(3)R2 and AC6 are specifically associated, and inhibition of AC6 or IP(3)R2 expression by small interfering RNA selectively attenuates potentiation of Ca(2+) signals by PTH.We define two modes of cAMP signaling: binary, where cAMP passes directly from AC6 to IP(3)R2; and analogue, where local gradients of cAMP concentration regulate cAMP effectors more remote from AC.Binary signaling requires localized delivery of cAMP, whereas analogue signaling is more dependent on localized cAMP degradation.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Univesrsity of Cambridge, Cambridge, England, UK.

ABSTRACT
Interactions between cyclic adenosine monophosphate (cAMP) and Ca(2+) are widespread, and for both intracellular messengers, their spatial organization is important. Parathyroid hormone (PTH) stimulates formation of cAMP and sensitizes inositol 1,4,5-trisphosphate receptors (IP(3)R) to IP(3). We show that PTH communicates with IP(3)R via "cAMP junctions" that allow local delivery of a supramaximal concentration of cAMP to IP(3)R, directly increasing their sensitivity to IP(3). These junctions are robust binary switches that are digitally recruited by increasing concentrations of PTH. Human embryonic kidney cells express several isoforms of adenylyl cyclase (AC) and IP(3)R, but IP(3)R2 and AC6 are specifically associated, and inhibition of AC6 or IP(3)R2 expression by small interfering RNA selectively attenuates potentiation of Ca(2+) signals by PTH. We define two modes of cAMP signaling: binary, where cAMP passes directly from AC6 to IP(3)R2; and analogue, where local gradients of cAMP concentration regulate cAMP effectors more remote from AC. Binary signaling requires localized delivery of cAMP, whereas analogue signaling is more dependent on localized cAMP degradation.

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Potentiation of CCh-stimulated Ca2+ release by 8-Br-cAMP. (A and B) Ca2+ signals evoked by 1 mM CCh alone (black) or after prior treatment (red) with 8-Br-cAMP (A; 10 mM for 20 min) or PTH (B; 100 nM for 1 min). Results (n > 3 from one experiment; means ± SEM) are typical of more than six experiments. (C and D) Effects of 8-Br-cAMP, 8-Br-2′-O-Me-cAMP (C), and PTH (D) on peak [Ca2+]i evoked by 1 mM CCh. (E) Effects of PTH (100 nM for 1 min) and 8-Br-cAMP (10 mM for 20 min) on CCh-evoked Ca2+ signals. (F) EC50 values and maximal responses (as a percentage of control) are shown for CCh-evoked Ca2+ signals after the indicated treatments. Results (C–F) are means ± SEM from at least three experiments. (G) cAMP entirely mediates potentiation of CCh-evoked Ca2+ release.
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fig2: Potentiation of CCh-stimulated Ca2+ release by 8-Br-cAMP. (A and B) Ca2+ signals evoked by 1 mM CCh alone (black) or after prior treatment (red) with 8-Br-cAMP (A; 10 mM for 20 min) or PTH (B; 100 nM for 1 min). Results (n > 3 from one experiment; means ± SEM) are typical of more than six experiments. (C and D) Effects of 8-Br-cAMP, 8-Br-2′-O-Me-cAMP (C), and PTH (D) on peak [Ca2+]i evoked by 1 mM CCh. (E) Effects of PTH (100 nM for 1 min) and 8-Br-cAMP (10 mM for 20 min) on CCh-evoked Ca2+ signals. (F) EC50 values and maximal responses (as a percentage of control) are shown for CCh-evoked Ca2+ signals after the indicated treatments. Results (C–F) are means ± SEM from at least three experiments. (G) cAMP entirely mediates potentiation of CCh-evoked Ca2+ release.

Mentions: PTH and a high concentration of the membrane-permeant analogue of cAMP, 8-Br-cAMP (30 mM), similarly potentiated CCh-evoked Ca2+ signals (Fig. 2, A–F); 8-Br-cGMP (30 mM) was ineffective (not depicted). Much lower (<100 μM) concentrations of 8-Br-cAMP activate PKA (He et al., 2003), but they did not significantly potentiate Ca2+ signals (Short and Taylor, 2000; Tovey et al., 2003). The low sensitivity to 8-Br-cAMP (half-maximal effective concentration, EC50 = 0.87 ± 0.37 mM; Fig. 2 C) is important and is discussed further in later sections.


Selective coupling of type 6 adenylyl cyclase with type 2 IP3 receptors mediates direct sensitization of IP3 receptors by cAMP.

Tovey SC, Dedos SG, Taylor EJ, Church JE, Taylor CW - J. Cell Biol. (2008)

Potentiation of CCh-stimulated Ca2+ release by 8-Br-cAMP. (A and B) Ca2+ signals evoked by 1 mM CCh alone (black) or after prior treatment (red) with 8-Br-cAMP (A; 10 mM for 20 min) or PTH (B; 100 nM for 1 min). Results (n > 3 from one experiment; means ± SEM) are typical of more than six experiments. (C and D) Effects of 8-Br-cAMP, 8-Br-2′-O-Me-cAMP (C), and PTH (D) on peak [Ca2+]i evoked by 1 mM CCh. (E) Effects of PTH (100 nM for 1 min) and 8-Br-cAMP (10 mM for 20 min) on CCh-evoked Ca2+ signals. (F) EC50 values and maximal responses (as a percentage of control) are shown for CCh-evoked Ca2+ signals after the indicated treatments. Results (C–F) are means ± SEM from at least three experiments. (G) cAMP entirely mediates potentiation of CCh-evoked Ca2+ release.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2568025&req=5

fig2: Potentiation of CCh-stimulated Ca2+ release by 8-Br-cAMP. (A and B) Ca2+ signals evoked by 1 mM CCh alone (black) or after prior treatment (red) with 8-Br-cAMP (A; 10 mM for 20 min) or PTH (B; 100 nM for 1 min). Results (n > 3 from one experiment; means ± SEM) are typical of more than six experiments. (C and D) Effects of 8-Br-cAMP, 8-Br-2′-O-Me-cAMP (C), and PTH (D) on peak [Ca2+]i evoked by 1 mM CCh. (E) Effects of PTH (100 nM for 1 min) and 8-Br-cAMP (10 mM for 20 min) on CCh-evoked Ca2+ signals. (F) EC50 values and maximal responses (as a percentage of control) are shown for CCh-evoked Ca2+ signals after the indicated treatments. Results (C–F) are means ± SEM from at least three experiments. (G) cAMP entirely mediates potentiation of CCh-evoked Ca2+ release.
Mentions: PTH and a high concentration of the membrane-permeant analogue of cAMP, 8-Br-cAMP (30 mM), similarly potentiated CCh-evoked Ca2+ signals (Fig. 2, A–F); 8-Br-cGMP (30 mM) was ineffective (not depicted). Much lower (<100 μM) concentrations of 8-Br-cAMP activate PKA (He et al., 2003), but they did not significantly potentiate Ca2+ signals (Short and Taylor, 2000; Tovey et al., 2003). The low sensitivity to 8-Br-cAMP (half-maximal effective concentration, EC50 = 0.87 ± 0.37 mM; Fig. 2 C) is important and is discussed further in later sections.

Bottom Line: Human embryonic kidney cells express several isoforms of adenylyl cyclase (AC) and IP(3)R, but IP(3)R2 and AC6 are specifically associated, and inhibition of AC6 or IP(3)R2 expression by small interfering RNA selectively attenuates potentiation of Ca(2+) signals by PTH.We define two modes of cAMP signaling: binary, where cAMP passes directly from AC6 to IP(3)R2; and analogue, where local gradients of cAMP concentration regulate cAMP effectors more remote from AC.Binary signaling requires localized delivery of cAMP, whereas analogue signaling is more dependent on localized cAMP degradation.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Univesrsity of Cambridge, Cambridge, England, UK.

ABSTRACT
Interactions between cyclic adenosine monophosphate (cAMP) and Ca(2+) are widespread, and for both intracellular messengers, their spatial organization is important. Parathyroid hormone (PTH) stimulates formation of cAMP and sensitizes inositol 1,4,5-trisphosphate receptors (IP(3)R) to IP(3). We show that PTH communicates with IP(3)R via "cAMP junctions" that allow local delivery of a supramaximal concentration of cAMP to IP(3)R, directly increasing their sensitivity to IP(3). These junctions are robust binary switches that are digitally recruited by increasing concentrations of PTH. Human embryonic kidney cells express several isoforms of adenylyl cyclase (AC) and IP(3)R, but IP(3)R2 and AC6 are specifically associated, and inhibition of AC6 or IP(3)R2 expression by small interfering RNA selectively attenuates potentiation of Ca(2+) signals by PTH. We define two modes of cAMP signaling: binary, where cAMP passes directly from AC6 to IP(3)R2; and analogue, where local gradients of cAMP concentration regulate cAMP effectors more remote from AC. Binary signaling requires localized delivery of cAMP, whereas analogue signaling is more dependent on localized cAMP degradation.

Show MeSH
Related in: MedlinePlus