Functional Specialization of Calreticulin Domains

• Published in: The Journal of cell biology Vol. 154; no. 5; pp. 961 - 972
• Main Authors: Nakamura, Kimitoshi, Zuppini, Anna, Arnaudeau, Serge, Lynch, Jeffery, Ahsan, Irfan, Krause, Ryoko, Papp, Sylvia, De Smedt, Humbert, Parys, Jan B., Müller-Esterl, Werner, Lew, Daniel P., Krause, Karl-Heinz, Demaurex, Nicolas, Opas, Michal, Michalak, Marek
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 03.09.2001; The Rockefeller University Press
• Subjects: Animals; Antibodies; B lymphocytes; Biochemistry; Bradykinin - pharmacology; Bradykinin receptors; Calcium; Calcium - metabolism; Calcium Channels - genetics; Calcium Channels - metabolism; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Calcium-Transporting ATPases - metabolism; Calreticulin; Cell Line; Cell lines; Cell surface receptors; Cells; Cellular biology; Embryos; Endoplasmic Reticulum - metabolism; Enzyme Inhibitors - pharmacology; Fibroblasts; Fibroblasts - drug effects; Fibroblasts - physiology; Flow Cytometry; Homeostasis; Immunoblotting; Inositol 1,4,5-Trisphosphate Receptors; Mathematical functions; Mice; Mice, Knockout; Microscopy, Fluorescence; Molecular Chaperones - genetics; Molecular Chaperones - metabolism; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein Structure, Tertiary; Receptors; Receptors, Bradykinin - metabolism; Receptors, Cytoplasmic and Nuclear - genetics; Receptors, Cytoplasmic and Nuclear - metabolism; Ribonucleoproteins - genetics; Ribonucleoproteins - metabolism; Rodents; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Thapsigargin - pharmacology; Transfection
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200102073

Calreticulin is a Ca2+-binding chaperone in the endoplasmic reticulum (ER), and calreticulin gene knockout is embryonic lethal. Here, we used calreticulin-deficient mouse embryonic fibroblasts to examine the function of calreticulin as a regulator of Ca2+homeostasis. In cells without calreticulin, the ER has a lower capacity for Ca2+storage, although the free ER luminal Ca2+concentration is unchanged. Calreticulin-deficient cells show inhibited Ca2+release in response to bradykinin, yet they release Ca2+upon direct activation with the inositol 1,4,5-triphosphate ( InsP3). These cells fail to produce a measurable level of InsP3upon stimulation with bradykinin, likely because the binding of bradykinin to its cell surface receptor is impaired. Bradykinin binding and bradykinin-induced Ca2+release are both restored by expression of full-length calreticulin and the N + P domain of the protein. Expression of the P + C domain of calreticulin does not affect bradykinin-induced Ca2+release but restores the ER Ca2+storage capacity. Our results indicate that calreticulin may play a role in folding of the bradykinin receptor, which affects its ability to initiate InsP3-dependent Ca2+release in calreticulin-deficient cells. We concluded that the C domain of calreticulin plays a role in Ca2+storage and that the N domain may participate in its chaperone functions.