earticle

영어

Development of agonistic antibody targeting TRAIL receptors (TRAIL-Rs/TRs/Death receptors) is an attractive strategy for the efficient anti-cancer therapy because the receptor-mediated pathway can induce cancer-selective cell death. We have recently isolated a human single-chain fragment variable, HW1, which specifically binds to TRAIL receptor 2 (TR2). Unlikely previously reported agonistic TR2-specific mAbs which induced apoptotic cell death, HW1 killed a variety of TRAIL-sensitive and -resistant cancer cells through autophagic cell death as a single agent showing much less cytotoxicity on normal cells. We also show that the HW1-mediated autophagic cell death occurs predominantly via the c-Jun NH2-terminal kinase (JNK) pathway in a caspase-independent manner. Analysis of the primary death-inducing signaling complex (DISC) induced by HW1 binding to TR2 exhibits the recruitment of TNF receptor-associated death domain (TRADD) and TNF receptor-associated factor 2 (TRAF2), but not Fas-associated death domain (FADD), caspase-8, or receptor-interacting protein (RIP). The subsequent secondary signaling complex retained the DISC components TRADD and TRAF2. Knocking down of TRADD/TRAF2 or MKK4/MKK7 by siRNA transfections attenuated JNK activation and significantly suppressed the HW1-induced cell death. Further, the combination of HW1 with Akt inhibitor, which blocked the inhibition of ASK1 by Akt, enhanced the cell death by 30% for cancer cells, compared with HW1 treatment alone. These results suggest that HW1-mediated JNK activation occurs through sequential signaling from TRADD/TRAF2, ASK1 to MKK4/MKK7. The next question is how HW1-mediated JNK activation preferentially induces autophagy to apoptosis in various tumors, even though JNK has been known to be associated with cell survival and apoptosis. We will present some data to discuss this conundrum mainly focusing on cross-regulations between apoptotic and autophagic molecules.