Selective degradation of IKKα by autophagy is essential for arsenite-induced cancer cell apoptosis

Abstract

Two catalytic subunits of the IKK complex, IKKα and IKKβ, trigger NF-κB activation as well as NF-κB-independent signaling events under both physiological and pathological conditions. Here we identified the NF-κB-unrelated cytoprotective function of IKKα in promoting autophagy by triggering p53 transactivation and upregulation of its downstream autophagic mediator, DRAM1, in the arsenite-treated hepatoma cells, which responses depended on IKKα kinase activity. Furthermore, IKKα triggered p53/DRAM1-dependent autophagy by inducing CHK1 activation and CHK1/p53 interaction. Interestingly, after provoking autophagy, IKKα could be specifically recognized by the autophagic machinery via directly binding with LC3B, resulting in selective degradation of IKKα by autophagy. Unexpectedly, the selectivity of autophagic sequestration towards IKKα was mediated by novel mechanism independent of the classical LC3-interacting regions (LIRs) within IKKα, while C-terminal arm of LIR was involved in mediating IKKα/LC3B interaction. Taken together, we conclude that IKKα attenuates arsenite-induced apoptosis by inducing p53-dependent autophagy, and then selective feedback degradation of IKKα by autophagy contributes to the cytotoxic response induced by arsenite.

Autophagic feedback-mediated degradation of IKKα requires CHK1- and p300/CBP-dependent acetylation of p53

“…In our previous reports, we demonstrated an NF-κB-independent role for IKKα in inducing cytoprotective autophagy by triggering CHK1-dependent p53 phosphorylation, which mediates the subsequent degradation of IKKα (Tan et al, 2020). In the current study, we further revealed the role of IKKα in coactivating CHK1and p300/CBP-dependent p53 acetylation, which is also involved in autophagy induction and the feedback control of IKKα expression, and, thereby, mediating arsenite cytotoxicity.…”

“…Next, we examined whether p53 transactivation was also regulated by p300/CBP-dependent p53 acetylation. To this end, p300 and CBP siRNAs were separately introduced into HepG2 cells stably transfected with a p53 luciferase reporter (Tan et al, 2020). Here, we found that upregulation of p53-dependent luciferase activity was also significantly inhibited by knocking down p300 or CBP expression (Fig.…”

“…In a previous report, we demonstrated that IKKα triggers its own feedback degradation by activating p53-dependent autophagy in HepG2 hepatoma cells under arsenite exposure. Interestingly, although IKKα is unable to interact with p53 directly, it plays a critical role in mediating p53 phosphorylation (at S15) by promoting CHK1 activation and CHK1-p53 complex formation (Tan et al, 2020). Since acetylation at lysine residues (such as K373 and/or K382; K373/382) also contributes substantially to p53 transactivation under stress conditions (Hafner et al, 2019), we wondered whether p53 acetylation was also involved in autophagic feedback degradation of IKKα during the arsenite response.…”

“…IKKα (encoded by CHUK) is one of the catalytic subunits of the IκB kinase (IKK) complex, and it shares structural similarity with another catalytic subunit, IKKβ (encoded by IKBKB) but triggers NF-κB activation by different mechanisms (Chariot, 2009;Huang and Hung, 2013). Furthermore, IKKα also possesses some unique functions that are independent of NF-κB activity and are mediated by NF-κB-unrelated substrates, such as Aurora A, Maspin, 14-3-3σ, SMRT, p53, SRC3, c-Fos, p85α, mTOR and ATG16L1 (Huang and Hung, 2013;Dong et al, 2012;Song et al, 2010;Tan et al, 2020). Therefore, it is believed that IKKα can act as a multifunctional signaling protein with roles going far beyond its well-known action in NF-κB pathway regulation.…”

DRAM1 plays a tumor suppressor role in NSCLC cells by promoting lysosomal degradation of EGFR

“…In response to starvation-induced apoptosis and autophagy, DRAM-induced mitophagy or autophagy contributes to apoptosis in hepatocellular carcinoma and breast cancer 27 , 28 . DRAM1 mediated autophagy can degrade IKKα to aggravate arsenite-induced cytotoxicity 29 . However, DRAM1 is also beneficial to cancer.…”