Abstract
Necroptosis is an inflammatory form of programmed cell death mediated by the pseudokinase mixed-lineage kinase domain-like protein (MLKL). Upon phosphorylation by receptor-interacting protein kinase-3 (RIPK3), MLKL oligomerizes, and translocates to and disrupts the plasma membrane, thereby causing necroptotic cell lysis. Herein, we show that activation of necroptosis in mouse dermal fibroblasts (MDFs) and HT-29 human colorectal cancer cells results in accumulation of the autophagic marker, lipidated LC3B (also known as MAP1LC3B), in an MLKL-dependent manner. Unexpectedly, the necroptosis-induced increase in lipidated LC3B was due to inhibition of autophagic flux, not the activation of autophagy. Inhibition of autophagy by MLKL correlated with a decrease in autophagosome and/or autolysosome function, and required the association of activated MLKL with intracellular membranes. Collectively, our findings uncover an additional role for the MLKL pseudokinase, namely to inhibit autophagy during necroptosis.