Sorafenib-induced defective autophagy promotes cell death by necroptosis

Abstract

Autophagy is one of the main cytoprotective mechanisms that cancer cells deploy to withstand the cytotoxic stress and survive the lethal damage induced by anti-cancer drugs. However, under specific conditions, autophagy may, directly or indirectly, induce cell death. In our study, treatment of the Atg5-deficient DU145 prostate cancer cells, with the multi-tyrosine kinase inhibitor, sorafenib, induces mitochondrial damage, autophagy and cell death. Molecular inhibition of autophagy by silencing ULK1 and Beclin1 rescues DU145 cells from cell death indicating that, in this setting, autophagy promotes cell death. Re-expression of Atg5 restores the lipidation of LC3 and rescues DU145 and MEF atg5−/− cells from sorafenib-induced cell death. Despite the lack of Atg5 expression and LC3 lipidation, DU145 cells form autophagosomes as demonstrated by transmission and immuno-electron microscopy, and the formation of LC3 positive foci. However, the lack of cellular content in the autophagosomes, the accumulation of long-lived proteins, the presence of GFP-RFP-LC3 positive foci and the accumulated p62 protein levels indicate that these autophagosomes may not be fully functional. DU145 cells treated with sorafenib undergo a caspase-independent cell death that is inhibited by the RIPK1 inhibitor, necrostatin-1. Furthermore, treatment with sorafenib induces the interaction of RIPK1 with p62, as demonstrated by immunoprecipitation and a proximity ligation assay. Silencing of p62 decreases the RIPK1 protein levels and renders necrostatin-1 ineffective in blocking sorafenib-induced cell death. In summary, the formation of Atg5-deficient autophagosomes in response to sorafenib promotes the interaction of p62 with RIPK leading to cell death by necroptosis.

Tetrandrine triggers an alternative autophagy in DU145 cells

“…2B). By contrast, a recent study reported that sorafenib induces EGFP-LC3 foci formation in DU145 cells (17). The results of the present study indicated that Tet could not induce EGFP-LC3 puncta formation, but it increased the number of autophagosomes in DU145 cells.…”

“…It may either lead to cell death or maintain cell survival against chemotherapeutic drugs. In DU145 cells, sorafenib blocks the autophagic flux, whereas transiently re-expressing ATG5 in DU145 cells antagonizes sorafenib-induced cell death (17). Therefore, the present authors postulate that the autophagic flux may be relatively inadequate in DU145 cells.…”

Cationic PEGylated liposomes incorporating an antimicrobial peptide tilapia hepcidin 2–3: an adjuvant of epirubicin to overcome multidrug resistance in cervical cancer cells

“…Accumulating studies have supported RIP1 as a key moderator of cell survival signaling, while other reports have suggested a prodeath role of RIP1. 22,24,55 Wang et al 22 have found that RIP1 played a crucial role in survival through catalase-mediated ROS reduction and maintenance of inhibitor of apoptosis proteins, thus enhancing chemoresistance to cisplatin in human lung cancer A549 cells. The activation of necropotosis was verified by the induction of RIP1 and RIP3, which was abrogated by necropotosis inhibitor necrostatin-1.…”

Differences and Similarities in TRAIL- and Tumor Necrosis Factor-Mediated Necroptotic Signaling in Cancer Cells

“…We have demonstrated that TRAIL-induced necroptosis is a signaling pathway distinct from autophagy; however, some studies suggest that necrosome assembly occurs on autophagosomal membranes, e.g., after treatment with obatoclax, an inhibitor of the antiapoptotic protein Bcl-2 (53), or with the multityrosine kinase inhibitor sorafenib (54). An involvement of the autophagic machinery during necroptosis is still controversial, as necroptosis was shown to be independent of autophagy in murine T cells lacking caspase-8 and FADD (55), but murine T cells deficient for caspase-8 and expressing dominant negative FADD undergo necroptosis via the activation of autophagy by RIPK1 (56).…”