Endoplasmic reticulum stress-mediated apoptosis of EBV-transformed B cells by CD70 signaling is dependent upon generation of reactive oxygen species and activation of p38 MAPK and JNK pathway (66.23)

Abstract

Abstract CD70 is expressed in normal activated immune cells as well as in several types of tumors. It has been established that anti-CD70 mAb induces complement-dependent death of CD70+ tumor cells, but how anti-CD70 mAb affects the intrinsic signaling is poorly defined. In this report, we show that ligation of CD70 expressed on EBV-transformed B cells induced production of reactive oxygen species (ROS) and subsequent apoptosis. We observed an early expression of endoplasmic reticulum (ER) stress response genes that preceded the release of apoptotic molecules from mitochondria and cleavage of caspases. CD70-induced apoptosis was inhibited by ER stress inhibitor salubrinal, ROS quencher NAC, and Ca2+ chelator BAPTA. We supposed that ROS generation might be the first event because NAC blocked increases of ROS and Ca2+, but BAPTA did not block ROS. We also found that CD70 stimulation activated JNK and p38. JNK inhibitor and p38 inhibitor blocked upregulation of ER stress-related genes and cleavage of caspases. Inhibition of ROS generation blocked phosphorylation of JNK and p38 and induction of ER stress-related genes. Taken together, we concluded that cross-linking of CD70 on EBVt- B cells triggered ER stress-mediated apoptosis via ROS generation and JNK and p38 MAPK activation. Our report reveals alternate mechanisms of direct apoptosis through CD70 signaling and provides data supporting CD70 as a viable target for an Ab-based therapy against EBV-related tumors.