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Functional specialization of calreticulin domains
K Nakamura1, A Zuppini, S Arnaudeau
1Canadian Institutes of Health Research Group in Molecular Biology of Membranes and the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
The Journal of Cell Biology
|August 29, 2001
Summary
Calreticulin deficiency impairs cellular calcium (Ca2+) storage and bradykinin receptor function. Restoring calreticulin or its domains rescues these deficits, highlighting its role in calcium homeostasis and receptor folding.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Calreticulin is a crucial Ca2+-binding chaperone within the endoplasmic reticulum (ER).
- Calreticulin gene knockout results in embryonic lethality, underscoring its vital functions.
- Its role in regulating Ca2+ homeostasis and cellular signaling pathways remains an area of active investigation.
Purpose of the Study:
- To investigate the function of calreticulin in Ca2+ homeostasis using calreticulin-deficient mouse embryonic fibroblasts.
- To elucidate the specific domains of calreticulin responsible for its various functions, including Ca2+ storage and bradykinin signaling.
- To understand the mechanism by which calreticulin influences bradykinin receptor activity and subsequent Ca2+ release.
Main Methods:
- Utilized calreticulin-deficient mouse embryonic fibroblasts for experimental analysis.
- Assessed ER Ca2+ storage capacity and free ER luminal Ca2+ concentrations.
- Measured Ca2+ release in response to bradykinin and inositol 1,4,5-trisphosphate (InsP3) stimulation.
- Investigated bradykinin binding to cell surface receptors.
- Analyzed the effects of expressing full-length calreticulin and its specific domains (N+P, P+C) on cellular functions.
Main Results:
- Calreticulin-deficient cells exhibit reduced ER Ca2+ storage capacity but unchanged free ER luminal Ca2+.
- These cells show impaired Ca2+ release upon bradykinin stimulation but retain responsiveness to direct InsP3 activation.
- Bradykinin-induced InsP3 production is significantly diminished in calreticulin-deficient cells, linked to impaired bradykinin receptor binding.
- Expression of full-length calreticulin or its N+P domain restored bradykinin binding and Ca2+ release.
- The P+C domain of calreticulin restored ER Ca2+ storage capacity but did not rescue bradykinin-induced Ca2+ release.
Conclusions:
- Calreticulin plays a critical role in maintaining ER Ca2+ storage capacity, primarily mediated by its C domain.
- The N domain of calreticulin is implicated in its chaperone functions, potentially including the folding of the bradykinin receptor.
- Impaired bradykinin receptor folding in calreticulin-deficient cells disrupts InsP3-dependent Ca2+ signaling, highlighting calreticulin's multifaceted role in cellular physiology.