Research Papers: Autophagy and Cell Death:
Sorafenib-induced defective autophagy promotes cell death by necroptosis
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Pedram Kharaziha1, Dimitris Chioureas1, George Baltatzis2, Pedro Fonseca1, Patricia Rodriguez3, Vladimir Gogvadze4, Lena Lennartsson1, Ann-Charlotte Björklund1, Boris Zhivotovsky4, Dan Grandér1, Lars Egevad1, Sten Nilsson1 and Theocharis Panaretakis1
1 Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet and University Hospital, Stockholm, Sweden
2 Department of Medicine, School of Health Sciences, University of Athens, Athens, Greece
3 Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden
4 Institute of Environmental Medicine, Division of Toxicology, Karolinska Institutet, Stockholm, Sweden
Theocharis Panaretakis, email:
Keywords: prostate cancer, tyrosine kinase inhibitor, autophagy, Atg5, necroptosis
Received: July 12, 2015 Accepted: August 29, 2015 Published: September 22, 2015
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.
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