Abstract
Stimulation of various cell surface receptors leads to the production of inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) through phospholipase C (PLC) activation, and the IP3 and DAG in turn trigger Ca2+ release through IP3 receptors and protein kinase C activation, respectively. The amount of IP(3) produced is particularly critical to determining the spatio-temporally coordinated Ca(2+)-signaling patterns. In this paper, we report a novel signal cross-talk between DAG and the IP3-mediated Ca(2+)-signaling pathway. We found that a DAG derivative, 1-oleoyl-2-acyl-sn-glycerol (OAG), induces Ca2+ oscillation in various types of cells independently of protein kinase C activity and extracellular Ca2+. The OAG-induced Ca2+ oscillation was completely abolished by depletion of Ca2+ stores or inhibition of PLC and IP3 receptors, indicating that OAG stimulates IP3 production through PLC activation and thereby induces IP3-induced Ca2+ release. Furthermore, intracellular accumulation of endogenous DAG by a DAG-lipase inhibitor greatly increased the number of cells responding to agonist stimulation at low doses. These results suggest a novel physiological function of DAG, i.e. amplification of Ca2+ signaling by enhancing IP3 production via its positive feedback effect on PLC activity.
Highlights
Stimulation of a wide variety of cells by hormones, neurotransmitters, or growth factors leads to the activation of phospholipase C (PLC)1 and triggers inositol 1,4,5-trisphosphate (IP3)-mediated Ca2ϩ signaling via activation of IP3 receptors (IP3Rs) on the endoplasmic reticulum [1, 2]
The OAG-induced Ca2ϩ oscillation was dependent on Ca2ϩ release through IP3Rs, because 2-aminoethyl diphenylborinate (2-APB) [18], an IP3R inhibitor, or depletion of Ca2ϩ stores with cyclopiazonic acid (CPA) abolished the Ca2ϩ mobilization
Between DAG and PLC activity may be a crucial mechanism regulating the amount of IP3, which is an important factor in determining the threshold of Ca2ϩ signaling generation and Ca2ϩ dynamics in response to agonist stimulation, and that it may play an important role in physiological phenomena that are dependent on IP3-induced Ca2ϩ release
Summary
Stimulation of a wide variety of cells by hormones, neurotransmitters, or growth factors leads to the activation of phospholipase C (PLC)1 and triggers inositol 1,4,5-trisphosphate (IP3)-mediated Ca2ϩ signaling via activation of IP3 receptors (IP3Rs) on the endoplasmic reticulum [1, 2]. 1-oleoyl-2-acyl-sn-glycerol (OAG), a membrane-permeable derivative of DAG, induces Ca2ϩ oscillation in COS-7 cells independently of PKC activity and extracellular Ca2ϩ.
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