Calcium-binding protein 1 is an inhibitor of agonist-evoked, inositol 1,4,5-trisphosphate-mediated calcium signaling.
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.
Haynes
Lee P
LP
The Physiological Laboratory, Crown Street, University of Liverpool, Liverpool L69 3BX, UK.
Tepikin
Alexei V
AV
Burgoyne
Robert D
RD
D017398:Alternative Splicing; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000502:physiology*; D003001:Cloning, Molecular; D014644:Genetic Variation; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D007700:Kinetics; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides / Q000502:physiology; D016716:PC12 Cells; D016133:Polymerase Chain Reaction; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D014162:Transfection
D002135:Calcium-Binding Proteins; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides; D011994:Recombinant Proteins; C101464:frequenin calcium sensor proteins; D015544:Inositol 1,4,5-Trisphosphate; C085577:Ca2+-binding protein-1