Binding of anti-GRP78 autoantibodies to cell surface GRP78 increases tissue factor procoagulant activity via the release of calcium from endoplasmic reticulum stores.
The increased risk of venous thromboembolism in cancer patients has been attributed to enhanced tissue factor (TF) procoagulant activity (PCA) on the surface of cancer cells. Recent studies have shown that TF PCA can be modulated by GRP78, an endoplasmic reticulum (ER)-resident molecular chaperone. In this study, we investigated the role of cell surface GRP78 in modulating TF PCA in several human cancer cell lines. Although both GRP78 and TF are present on the cell surface of cancer cells, there was no evidence of a stable interaction between recombinant human GRP78 and TF, nor was there any effect of exogenously added recombinant GRP78 on cell surface TF PCA. Treatment of cells with the ER stress-inducing agent thapsigargin, an inhibitor of the sarco(endo)plasmic reticulum Ca(2+) pump that causes Ca(2+) efflux from ER stores, increased cytosolic [Ca(2+)] and induced TF PCA. Consistent with these findings, anti-GRP78 autoantibodies that were isolated from the serum of patients with prostate cancer and bind to a specific N-terminal epitope (Leu(98)-Leu(115)) on cell surface GRP78, caused a dose-dependent increase in cytosolic [Ca(2+)] and enhanced TF PCA. The ability to interfere with cell surface GRP78 binding, block phospholipase C activity, sequester ER Ca(2+), or prevent plasma membrane phosphatidylserine exposure resulted in a significant decrease in the TF PCA induced by anti-GRP78 autoantibodies. Taken together, these findings provide evidence that engagement of the anti-GRP78 autoantibodies with cell surface GRP78 increases TF PCA through a mechanism that involves the release of Ca(2+) from ER stores. Furthermore, blocking GRP78 signaling on the surface of cancer cells attenuates TF PCA and has the potential to reduce the risk of cancer-related venous thromboembolism.
Al-Hashimi
Ali A
AA
Department of Medicine and Division of Nephrology, St Joseph's Hospital and McMaster University, Hamilton, Ontario L8N 4A6, Canada.
Caldwell
Jennifer
J
Gonzalez-Gronow
Mario
M
Pizzo
Salvatore V
SV
Aboumrad
Danya
D
Pozza
Lindsay
L
Al-Bayati
Hiam
H
Weitz
Jeffrey I
JI
Stafford
Alan
A
Chan
Howard
H
Kapoor
Anil
A
Jacobsen
Donald W
DW
Dickhout
Jeffrey G
JG
Austin
Richard C
RC
D000912:Antibodies, Neoplasm / Q000276:immunology* / Q000378:metabolism / Q000494:pharmacology; D001323:Autoantibodies / Q000276:immunology* / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000276:immunology* / Q000378:metabolism; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000276:immunology* / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000939:Epitopes / Q000276:immunology / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D008297:Male; D010718:Phosphatidylserines / Q000276:immunology / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000150:complications / Q000276:immunology* / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D019284:Thapsigargin / Q000494:pharmacology; D013925:Thromboplastin / Q000276:immunology* / Q000378:metabolism; D010738:Type C Phospholipases / Q000276:immunology / Q000378:metabolism; D054556:Venous Thromboembolism / Q000209:etiology / Q000276:immunology* / Q000378:metabolism
D000912:Antibodies, Neoplasm; D001323:Autoantibodies; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; D000939:Epitopes; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D010718:Phosphatidylserines; D019284:Thapsigargin; D013925:Thromboplastin; D010738:Type C Phospholipases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium