Oxysterol-binding protein related-proteins (ORPs) 5 and 8 regulate calcium signaling at specific cell compartments

Ilari Pulli, T Lassila, G Pan, D Yan, VM Olkkonen, Kid Törnquist

Research output: Contribution to journalArticleScientificpeer-review

27 Citations (Scopus)


Oxysterol-binding protein related-protein 5 and 8 (ORP5/8) localize to the membrane contact sites (MCS) of the endoplasmic reticulum (ER) and the mitochondria, as well as to the ER-plasma membrane (PM) MCS. The MCS are emerging as important regulators of cell signaling events, including calcium (Ca2+) signaling. ORP5/8 have been shown to interact with phosphatidylinositol-4,5-bisphosphate (PIP2) in the PM, and to modulate mitochondrial respiration and morphology. PIP2 is the direct precursor of inositol trisphosphate (IP3), a key second messenger responsible for Ca2+-release from the intracellular Ca2+ stores. Further, mitochondrial respiration is linked to Ca2+ transfer from the ER to the mitochondria. Hence, we asked whether ORP5/8 would affect Ca2+ signaling in these cell compartments, and employed genetically engineered aequorin Ca2+ probes to investigate the effect of ORP5/8 in the regulation of mitochondrial and caveolar Ca2+. Our results show that ORP5/8 overexpression leads to increased mitochondrial matrix Ca2+ as well as to increased Ca2+ concentration at the caveolar subdomains of the PM during histamine stimulation, while having no effect on the cytoplasmic Ca2+. Also, we found that ORP5/8 overexpression increases cell proliferation. Our results show that ORP5/8 regulate Ca2+ signaling at specific MCS foci. These local ORP5/8-mediated Ca2+ signaling events are likely to play roles in processes such as mitochondrial respiration and cell proliferation.
Original languageUndefined/Unknown
Pages (from-to)62–69
Number of pages8
JournalCell Calcium
Publication statusPublished - 2018
MoE publication typeA1 Journal article-refereed


  • ORP5
  • ORP8
  • Endoplasmic reticulum
  • caveolae
  • Mitochondria

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