Functional specialization of calreticulin domains.
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-trisphosphate (InsP3). These cells fail to produce a measurable level of InsP3 upon 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.
Nakamura
K
K
Canadian Institutes of Health Research Group in Molecular Biology of Membranes and the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
Zuppini
A
A
Arnaudeau
S
S
Lynch
J
J
Ahsan
I
I
Krause
R
R
Papp
S
S
De Smedt
H
H
Parys
J B
JB
Muller-Esterl
W
W
Lew
D P
DP
Krause
K H
KH
Demaurex
N
N
Opas
M
M
Michalak
M
M
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D037282:Calreticulin; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology; D005434:Flow Cytometry; D006706:Homeostasis; D015151:Immunoblotting; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D018002:Receptors, Bradykinin / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D004791:Enzyme Inhibitors; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018832:Molecular Chaperones; D020033:Protein Isoforms; D018002:Receptors, Bradykinin; D018160:Receptors, Cytoplasmic and Nuclear; D012261:Ribonucleoproteins; D019284:Thapsigargin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D001920:Bradykinin; D002118:Calcium