Posttranslational neddylation of
cullins in the
Cullin-Ring
E3 ligase (CRL) complexes is needed for proteolytic degradation of CRL substrates, whose accumulation induces cell-cycle arrest, apoptosis, and senescence. The Nedd8-activating
enzyme (NAE) is critical for neddylation of CRL complexes and their growth-promoting function. Recently, the anticancer small molecule
MLN4924 currently in phase I trials was determined to be an inhibitor of NAE that blocks
cullin neddylation and inactivates CRL, triggering an accumulation of CRL substrates that trigger cell-cycle arrest, apoptosis, and senescence in
cancer cells. Here, we report that
MLN4924 also triggers autophagy in response to CRL inactivation and that this effect is important for the ability of
MLN4924 to suppress the outgrowth of
liver cancer cells in vitro and in vivo. MLN4924-induced autophagy was attributed partially to inhibition of mTOR activity, due to accumulation of the mTOR inhibitory
protein Deptor, as well as to induction of
reactive oxygen species stress. Inhibiting autophagy enhanced MLN4924-induced apoptosis, suggesting that autophagy is a survival signal triggered in response to CRL inactivation. In a xenograft model of human
liver cancer,
MLN4924 was well-tolerated and displayed a significant antitumor effect characterized by CRL inactivation and induction of autophagy and apoptosis in
liver cancer cells. Together, our findings support the clinical investigation of
MLN4924 for
liver cancer treatment and provide a preclinical proof-of-concept for combination
therapy with an autophagy inhibitor to enhance therapeutic efficacy.