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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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Related in: MedlinePlus

Quantification of signaling proteins. (A–D) Equilibrium competition binding curves for each of the ligands are shown. Results show the expression levels of PTH receptors (A), β-adrenoceptors (B), AC (C), and IP3R (D) in HEK-PR1 cells. (E) Summary of the numbers of the signaling proteins expressed in each HEK-PR1 cell. For Gαs, this was calculated from calibrated WB, and for receptors and FK, it was computed from the Kd and the specific binding (S) determined for a defined concentration ([L]) of radioligand of known specific activity with the formula: Bmax = S(1+[L]/Kd). Means ± SEM, n ≥ 3.
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fig8: Quantification of signaling proteins. (A–D) Equilibrium competition binding curves for each of the ligands are shown. Results show the expression levels of PTH receptors (A), β-adrenoceptors (B), AC (C), and IP3R (D) in HEK-PR1 cells. (E) Summary of the numbers of the signaling proteins expressed in each HEK-PR1 cell. For Gαs, this was calculated from calibrated WB, and for receptors and FK, it was computed from the Kd and the specific binding (S) determined for a defined concentration ([L]) of radioligand of known specific activity with the formula: Bmax = S(1+[L]/Kd). Means ± SEM, n ≥ 3.

Mentions: Our analysis of AC and IP3R expression (Table I and Fig. 8) suggest that a HEK cell expresses ∼1,500 AC6 and ∼13,300 IP3R2 subunits (∼3,300 homotetrameric IP3R2), and at least 30% of IP3R2 (∼1,000 IP3R) are associated with AC6 (Fig. 7 B). These estimates cannot reliably define the stoichiometry of the IP3R2–AC6 complex, but they are consistent with each AC6 associating with a single tetrameric IP3R2 (Fig. 7 E).


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)

Quantification of signaling proteins. (A–D) Equilibrium competition binding curves for each of the ligands are shown. Results show the expression levels of PTH receptors (A), β-adrenoceptors (B), AC (C), and IP3R (D) in HEK-PR1 cells. (E) Summary of the numbers of the signaling proteins expressed in each HEK-PR1 cell. For Gαs, this was calculated from calibrated WB, and for receptors and FK, it was computed from the Kd and the specific binding (S) determined for a defined concentration ([L]) of radioligand of known specific activity with the formula: Bmax = S(1+[L]/Kd). Means ± SEM, n ≥ 3.
© Copyright Policy
Related In: Results  -  Collection

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

fig8: Quantification of signaling proteins. (A–D) Equilibrium competition binding curves for each of the ligands are shown. Results show the expression levels of PTH receptors (A), β-adrenoceptors (B), AC (C), and IP3R (D) in HEK-PR1 cells. (E) Summary of the numbers of the signaling proteins expressed in each HEK-PR1 cell. For Gαs, this was calculated from calibrated WB, and for receptors and FK, it was computed from the Kd and the specific binding (S) determined for a defined concentration ([L]) of radioligand of known specific activity with the formula: Bmax = S(1+[L]/Kd). Means ± SEM, n ≥ 3.
Mentions: Our analysis of AC and IP3R expression (Table I and Fig. 8) suggest that a HEK cell expresses ∼1,500 AC6 and ∼13,300 IP3R2 subunits (∼3,300 homotetrameric IP3R2), and at least 30% of IP3R2 (∼1,000 IP3R) are associated with AC6 (Fig. 7 B). These estimates cannot reliably define the stoichiometry of the IP3R2–AC6 complex, but they are consistent with each AC6 associating with a single tetrameric IP3R2 (Fig. 7 E).

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