Calcium-binding Protein 1 Is an Inhibitor of Agonist-evoked, Inositol 1,4,5-Trisphosphate-mediated Calcium Signaling

• Published in: The Journal of biological chemistry Vol. 279; no. 1; pp. 547 - 555
• Main Authors: Haynes, Lee P., Tepikin, Alexei V., Burgoyne, Robert D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02.01.2004; American Society for Biochemistry and Molecular Biology
• Subjects: Alternative Splicing; Animals; Calcium Signaling - physiology; Calcium-Binding Proteins - physiology; Cloning, Molecular; Genetic Variation; Humans; Inositol 1,4,5-Trisphosphate - antagonists & inhibitors; Inositol 1,4,5-Trisphosphate - pharmacology; Kinetics; Neuronal Calcium-Sensor Proteins; Neuropeptides - physiology; PC12 Cells; Polymerase Chain Reaction; Rats; Recombinant Proteins - metabolism; Signal Transduction - drug effects; Signal Transduction - genetics; Signal Transduction - physiology; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M309617200

Intracellular calcium signals are responsible for initiating a spectrum of physiological responses. The caldendrins/calcium-binding proteins (CaBPs) represent mammal-specific members of the CaM superfamily. CaBPs display a restricted pattern of expression in neuronal/retinal tissues, suggesting a specialized role in Ca2+ signaling in these cell types. Recently, it was reported that a splice variant of CaBP1 functionally interacts with inositol 1,4,5-trisphosphate (InsP3) receptors to elicit channel activation in the absence of InsP3 (Yang, J., McBride, S., Mak, D.-O. D., Vardi, N., Palczewski, K., Haeseleer, F., and Foskett, J. K. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 7711–7716). These data indicate a new mode of InsP3 receptor modulation and hence control of intracellular Ca2+ concentration ([Ca2+]i) in neuronal tissues. We have analyzed the biochemistry of the long form splice variant of CaBP1 (L-CaBP1) and show that, in vitro, a recombinant form of the protein is able to bind Ca2+ with high affinity and undergo a conformational change. We also describe the localization of endogenous and overexpressed L-CaBP1 in the model neuroendocrine PC12 cell system, where it was associated with the plasma membrane and Golgi complex in a myristoylation-dependent manner. Furthermore, we show that overexpressed L-CaBP1 is able to substantially suppress rises in [Ca2+]i in response to physiological agonists acting on purinergic receptors and that this inhibition is due in large part to blockade of release from intracellular Ca2+ stores. The related protein neuronal calcium sensor-1 was without effect on the [Ca2+]i responses to agonist stimulation. Measurement of [Ca2+] within the ER of permeabilized PC12 cells demonstrated that LCaBP1 directly inhibited InsP3-mediated Ca2+ release. Expression of L-CaBP1 also inhibited histamine-induced [Ca2+]i oscillations in HeLa cells. Together, these data suggest that L-CaBP1 is able to specifically regulate InsP3 receptor-mediated alterations in [Ca2+]i during agonist stimulation.