Figure 4. The mechanism of up-regulation of RIP1 phosphorylation and LC-3II in z-VAD-FMK-induced photoreceptor necroptosis. When cells undergo tumor necrosis factor (TNF)-induced apoptosis, RIP1 phosphorylation is inactivated by caspase-8. Caspase inhibitor, z-VAD-FMK, can switch the death receptor induced apoptotic response to necroptosis by inhibition caspases-8 activation and up-regulation RIP1 phosphorylation. Then RIP1 phosphorylation can induce the activation of autophagy marker LC-3II by a currently unknown pathway.