title: A novel chimeric aequorin fused with caveolin-1 reveals a sphingosine kinase 1-regulated Ca²⁺ microdomain in the caveolar compartment.
abstract: Caveolae are plasma membrane invaginations enriched in sterols and sphingolipids. Sphingosine kinase 1 (SK1) is an oncogenic protein that converts sphingosine to sphingosine 1-phosphate (S1P), which is a messenger molecule involved in calcium signaling. Caveolae contain calcium responsive proteins, but the effects of SK1 or S1P on caveolar calcium signaling have not been investigated. We generated a Caveolin-1-Aequorin fusion protein (Cav1-Aeq) that can be employed for monitoring the local calcium concentration at the caveolae ([Ca²⁺]cav). In HeLa cells, Cav1-Aeq reported different [Ca²⁺] as compared to the plasma membrane [Ca²⁺] in general (reported by SNAP25-Aeq) or as compared to the cytosolic [Ca²⁺] (reported by cyt-Aeq). The Ca²⁺ signals detected by Cav1-Aeq were significantly attenuated when the caveolar structures were disrupted by methyl-β-cyclodextrin, suggesting that the caveolae are specific targets for Ca²⁺ signaling. HeLa cells overexpressing SK1 showed increased [Ca²⁺]cav during histamine-induced Ca²⁺ mobilization in the absence of extracellular Ca²⁺ as well as during receptor-operated Ca²⁺ entry (ROCE). The SK1-induced increase in [Ca²⁺]cav during ROCE was reverted by S1P receptor antagonists. In accordance, pharmacologic inhibition of SK1 reduced the [Ca²⁺]cav during ROCE. S1P treatment stimulated the [Ca²⁺]cav upon ROCE. The Ca²⁺ responses at the plasma membrane in general were not affected by SK1 expression. In summary, our results show that SK1/S1P-signaling regulates Ca²⁺ signals at the caveolae. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.
authors.affiliation: Åbo Akademi University, Tykistökatu 6A, 20520 Turku, Finland.
authors.forename: Ilari
authors.initials: I
authors.lastname: Pulli
authors.affiliation: University Of Helsinki, 00014 Helsinki, Finland.
authors.forename: Tomas
authors.initials: T
authors.lastname: Blom
authors.affiliation: University Of Turku, Department of Physiology, Institute of Biomedicine, Kiinamyllynkatu 10, 20520 Turku, Finland.
authors.forename: Christoffer
authors.initials: C
authors.lastname: Löf
authors.affiliation: Åbo Akademi University, Tykistökatu 6A, 20520 Turku, Finland.
authors.forename: Melissa
authors.initials: M
authors.lastname: Magnusson
authors.affiliation: University of Ferrara, Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), 44121 Ferrara, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rimessi
authors.affiliation: University of Ferrara, Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), 44121 Ferrara, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Pinton
authors.affiliation: Åbo Akademi University, Tykistökatu 6A, 20520 Turku, Finland; Minerva Foundation Institute For Medical Research, Biomedicum Helsinki, 00270 Helsinki, Finland. Electronic address: ktornqvi@abo.fi.
authors.forename: Kid
authors.initials: K
authors.lastname: Törnquist
mesh_terms: D000331:Aequorin / Q000096:biosynthesis* / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D021941:Caveolae / Q000378:metabolism*; D051242:Caveolin 1 / Q000096:biosynthesis* / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008246:Lysophospholipids / Q000494:pharmacology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis* / Q000235:genetics; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000099157:Sphingosine Kinase
chemical_list: D000331:Aequorin; D002118:Calcium; D051242:Caveolin 1; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D011993:Recombinant Fusion Proteins; D013110:Sphingosine; D000099157:Sphingosine Kinase; C495540:CAV1 protein, human; C060506:sphingosine 1-phosphate
keywords: Aequorin; Calcium; Caveolin-1; Plasma membrane; Sphingosine kinase 1; Sphingosine-1-phosphate