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Role of calreticulin in regulating intracellular Ca2+ storage and capacitative Ca2+ entry in HeLa cells

Roderick, H. L., Llewellyn, David H., Campbell, Anthony Keith and Kendall, Jonathan M. 1998. Role of calreticulin in regulating intracellular Ca2+ storage and capacitative Ca2+ entry in HeLa cells. Cell Calcium 24 (4) , pp. 253-262. 10.1016/S0143-4160(98)90049-5

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Calreticulin is a Ca2+ binding protein located primarily in the endoplasmic reticulum (ER) lumen of nonexcitable cells, where it is considered to be involved mainly in Ca2+storage and buffering. However, there is increasing evidence to implicate the protein in other facets of Ca2+ signalling. In this study, we sought to establish more clearly the role of the protein in the regulation of intracellular Ca2+ signalling. Generating HeLacells stably transfected with GFP-tagged calreticulin (GFPCRT) allowed to us to select cells by FACS in which calreticulin was expressed at ten times its endogenous levels. Using transiently expressed aequorin as a Ca2+ indicator in these cells, we investigated the role of calreticulin in intracellular Ca2+storage, IP3-mediated Ca2+ release, and capacitative Ca2+entry. The data showed that the capacity of the ionomycin-sensitive Ca2+ store was doubled in over-expressing cells, indicating that although calreticulin has a role in Ca2+storage within the lumen, other lumenal proteins are also likely to be involved. No difference was observed in the release of Ca2+ from the IP3-sensitive store in response to prolonged single stimulation with histamine in the absence of extracellular Ca2+, but use of short, sequential pulses of histamine and ATP revealed that calreticulin may exert an effect upon IP3-mediated Ca2+ release. Two different experimental approaches indicated that calreticulin participates in the regulation of capacitative Ca2+entry. In the presence of extracellular Ca2+, the histamine-generated cytosolic Ca2+ signal was significantly lower in GFPCRT cells than those in control cells. Induction of capacitative Ca2+entry by complete emptying of the store using the SERCA pump inhibitor, cyclopiazonic acid also showed that the influx component was significantly reduced in the GFPCRT cells. Use of ER-targeted apoaequorin acting as a luciferase demonstrated that the resting ER free [Ca2+] in the GFPCRT cells was lower than that in control cells. These data implicate calreticulin in the control of IP3-mediated Ca2+ release and capacitative Ca2+entry, which may involve direct interaction with Ca2+ signalling components or control of ER free [Ca2+].

Item Type: Article
Date Type: Publication
Status: Published
Schools: Medicine
Subjects: Q Science > QD Chemistry
R Medicine > RM Therapeutics. Pharmacology
Publisher: Elsevier
ISSN: 0143-4160
Last Modified: 05 Jun 2017 02:58

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