The thioxotriazole copper(II) complex A0 induces endoplasmic reticulum stress and paraptotic death in human cancer cells.
The copper(II) complex A0 induces a type of non-apoptotic cell death also known as paraptosis. Paraptosis involves extensive endoplasmic reticulum vacuolization in the absence of caspase activation. A wide panel of human cancer cell lines was used to demonstrate differences in cytotoxicity by the paraptosis-inducing drug A0 and the metal-based pro-apoptotic drug cisplatin. Gene expression profiling of the human fibrosarcoma HT1080 cells showed that, while cisplatin induced p53 targets, A0 up-regulated genes involved in the unfolded protein response (UPR) and response to heavy metals. The cytotoxic effects of A0 were associated with inhibition of the ubiquitin-proteasome system and accumulation of ubiquitinylated proteins, in a manner dependent on protein synthesis. Cycloheximide inhibited the accumulation of ubiquitinylated proteins and hampered A0-induced cell death process. The occurrence of the UPR during A0-induced death process was shown by the increased abundance of spliced XBP1 mRNA, transient eIF2alpha phosphorylation, and a series of downstream events, including attenuation of global protein synthesis and increased expression of ATF4, CHOP, BIP, and GADD34. Mouse embryonic fibroblasts expressing a mutant eIF2alpha, which could not be phosphorylated, were more resistant to A0 than wild type cells, pointing to a pro-death role of eIF2alpha phosphorylation. A0 may thus represent the prototypical member of a new class of compounds that cause paraptotic cell death via mechanisms involving eIF2alpha phosphorylation and the UPR.
Tardito
Saverio
S
Unit of General and Clinical Pathology, Department of Experimental Medicine, University of Parma, Parma, Italy.
Isella
Claudio
C
Medico
Enzo
E
Marchiò
Luciano
L
Bevilacqua
Elena
E
Hatzoglou
Maria
M
Bussolati
Ovidio
O
Franchi-Gazzola
Renata
R
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D018938:Caco-2 Cells; D002945:Cisplatin / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology* / Q000627:therapeutic use; D004354:Drug Screening Assays, Antitumor; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D009942:Organometallic Compounds / Q000494:pharmacology* / Q000627:therapeutic use; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects*; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects
D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; D009942:Organometallic Compounds; D012333:RNA, Messenger; D025801:Ubiquitin; D003300:Copper; D046988:Proteasome Endopeptidase Complex; D002945:Cisplatin