A Novel Ca2+-induced Ca2+ Release Mechanism in A7r5 Cells Regulated by Calmodulin-like Proteins

• Published in: The Journal of biological chemistry Vol. 278; no. 30; pp. 27548 - 27555
• Main Authors: Kasri, Nael Nadif, Sienaert, Ilse, Parys, Jan B., Callewaert, Geert, Missiaen, Ludwig, Jeromin, Andreas, De Smedt, Humbert
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 25-07-2003; American Society for Biochemistry and Molecular Biology
• Subjects: Adenosine Triphosphate - pharmacology; Amino Acid Motifs; Animals; Calcium - metabolism; Calmodulin - metabolism; Cells, Cultured; Cloning, Molecular; Dose-Response Relationship, Drug; Humans; Magnesium - metabolism; Mice; Peptide Biosynthesis; Protein Structure, Tertiary; Rats; Ryanodine Receptor Calcium Release Channel - metabolism; Signal Transduction; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M302026200

Intracellular Ca2+ release is involved in setting up Ca2+ signals in all eukaryotic cells. Here we report that an increase in free Ca2+ concentration triggered the release of up to 41 ± 3% of the intracellular Ca2+ stores in permeabilized A7r5 (embryonic rat aorta) cells with an EC50 of 700 nm. This type of Ca2+-induced Ca2+ release (CICR) was neither mediated by inositol 1,4,5-trisphosphate receptors nor by ryanodine receptors, because it was not blocked by heparin, 2-aminoethoxydiphenyl borate, xestospongin C, ruthenium red, or ryanodine. ATP dose-dependently stimulated the CICR mechanism, whereas 10 mm MgCl2 abolished it. CICR was not affected by exogenously added calmodulin (CaM), but CaM1234, a Ca2+-insensitive CaM mutant, strongly inhibited the CICR mechanism. Other proteins of the CaM-like neuronal Ca2+-sensor protein family such as Ca2+-binding protein 1 and neuronal Ca2+ sensor-1 were equally potent for inhibiting the CICR. Removal of endogenous CaM, using a CaM-binding peptide derived from the ryanodine receptor type-1 (amino acids 3614–3643) prevented subsequent activation of the CICR mechanism. A similar CICR mechanism was also found in 16HBE14o-(human bronchial mucosa) cells. We conclude that A7r5 and 16HBE14o-cells express a novel type of CICR mechanism that is silent in normal resting conditions due to inhibition by CaM but becomes activated by a Ca2+-dependent dissociation of CaM. This CICR mechanism, which may be regulated by members of the family of neuronal Ca2+-sensor proteins, may provide an additional route for Ca2+ release that could allow amplification of small Ca2+ signals.