Calreticulin is released from activated neutrophils and binds to C1q and mannan-binding protein.
The Ca2+ storage protein calreticulin is associated with the endoplasmic reticulum and shares a high degree of amino acid homology with the surface receptor C1q-R. In this study, flow cytometric analysis detected calreticulin on the neutrophil surface, which decreased during stimulation probably as a consequence of shedding, as calreticulin was found by ELISA in the cell supernatants of stimulated cells. Antibodies raised against C1q-R and calreticulin demonstrated a high degree of immunological cross-reactivity for purified calreticulin as determined by dot blot analysis. Western blots of neutrophil subcellular fractions located calreticulin in both the cytosol and cell membrane fractions; C1q-R was largely confined to the cell membrane. Calreticulin and C1q-R both bind to C1q and mannan-binding protein. Therefore, calreticulin may be shed on cell activation and may be associated with the cell membrane, where it can potentially interact with C1q and serum lectins. The implications of this are discussed.
Eggleton
P
P
Department of Pathology, Boston University School of Medicine, Massachusetts 02118.
Lieu
T S
TS
Zappi
E G
EG
Sastry
K
K
Coburn
J
J
Zaner
K S
KS
Sontheimer
R D
RD
Capra
J D
JD
Ghebrehiwet
B
B
Tauber
A I
AI
D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*; D037282:Calreticulin; D002352:Carrier Proteins / Q000378:metabolism*; D037222:Collectins; D015922:Complement C1q / Q000276:immunology / Q000378:metabolism*; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D037102:Lectins / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000276:immunology; D012261:Ribonucleoproteins / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*
D002135:Calcium-Binding Proteins; D037282:Calreticulin; D002352:Carrier Proteins; D037222:Collectins; D037102:Lectins; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; D015922:Complement C1q