Overexpression of calreticulin increases intracellular Ca2+ storage and decreases store-operated Ca2+ influx

Laurence Mery, Nasrin Mesaeli, Marek Michalak, Michal Opas, Daniel P. Lew, Karl Heinz Krause

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The widely distributed and highly conserved Ca2+-binding protein calreticulin has been suggested to play a role as a Ca2+ storage protein of intracellular Ca2+ stores. To test this hypothesis, we have generated a mouse L fibroblast cell line stably transfected with a calreticulin expression vector. The calreticulin content of the overexpressers was increased by 1.6 ± 0.2-fold compared with mock-transfected cells. The total cellular Ca2+ content of calreticulin-overexpressing and control cells, as assessed by equilibrium 45Ca2+ uptake, was 141 ± 8 and 67 ± 6 pmol of Ca2+/106 cells, respectively (i.e. a 2.1 ± 0.2-fold increase in the Ca2+ content of calreticulin-overexpressing cells). Over 80% of the increased Ca2+ content was found within thapsigargin-sensitive Ca2+ stores. The pattern of calreticulin distribution, revealed by immunofluorescence microscopy, showed an endoplasmic reticulum-like pattern and was identical in overexpressers and control cells. In overexpressers, cytosolic free [Ca2+] elevations due to Ca2+ release were enhanced when either ATP or a combination of ionomycin and thapsigargin was used as a stimulus. In contrast, thapsigargin-induced Ca2+ and Mn2+ influxes from the extracellular space were markedly diminished in calreticulin-overexpressing cells, suggesting an active involvement of calreticulin in the regulation of store-operated Ca2+ influx.

Original languageEnglish
Pages (from-to)9332-9339
Number of pages8
JournalJournal of Biological Chemistry
Issue number16
Publication statusPublished - 19 Apr 1996


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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