Phosphorylation of inositol 1,4,5-trisphosphate receptors in parotid acinar cells: A mechanism for the synergistic effects of cAMP on Ca2+ signaling

Jason I E Bruce, Trevor J. Shuttleworth, David R. Giovannucci, David I. Yule

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Acetylcholine-evoked secretion from the parotid gland is substantially potentiated by cAMP-raising agonists. A potential locus for the action of cAMP is the intracellular signaling pathway resulting in elevated cytosolic calcium levels ([Ca2+]i). This hypothesis was tested in mouse parotid acinar cells. Forskolin dramatically potentiated the carbachol-evoked increase in [Ca2+]i, converted oscillatory [Ca2+]i changes into a sustained [Ca2+]i increase, and caused subthreshold concentrations of carbachol to increase [Ca2+]i measurably. This potentiation was found to be independent of Ca2+ entry and inositol 1,4,5-trisphosphate (InsP3) production, suggesting that cAMP-mediated effects on Ca2+ release was the major underlying mechanism. Consistent with this hypothesis, dibutyryl cAMP dramatically potentiated InSP3-evoked Ca2+ release from streptolysin-O-permeabilized cells. Furthermore, type II InsP3 receptors (InsP3R) were shown to be directly phosphorylated by a protein kinase A (PKA)-mediated mechanism after treatment with forskolin. In contrast, no evidence was obtained to support direct PKA-mediated activation of ryanodine receptors (RyRs). However, inhibition of RyRs in intact cells, demonstrated a role for RyRs in propagating Ca2+ oscillations and amplifying potentiated Ca2+ release from InsP3Rs. These data indicate that potentiation of Ca2+ release is primarily the result of PKA-mediated phosphorylation of InsP3Rs, and may largely explain the synergistic relationship between cAMP-raising agonists and acetylcholine-evoked secretion in the parotid. In addition, this report supports the emerging consensus that phosphorylation at the level of the Ca2+ release machinery is a broadly important mechanism by which cells can regulate Ca2+-mediated processes.
    Original languageEnglish
    Pages (from-to)1340-1348
    Number of pages8
    JournalJournal of Biological Chemistry
    Volume277
    Issue number2
    DOIs
    Publication statusPublished - 11 Jan 2002

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