Characterization of caspase-dependent and caspase-independent deaths in glioblastoma cells treated with inhibitors of the ubiquitin-proteasome system

Abstract

The regulation of the necrotic death and its relevance in anticancer therapy are largely unknown. Here, we have investigated the proapoptotic and pronecrotic activities of two ubiquitin-proteasome system inhibitors: bortezomib and G5. The present study points out that the glioblastoma cell lines U87MG and T98G are useful models to study the susceptibility to apoptosis and necrosis in response to ubiquitin-proteasome system inhibitors. U87MG cells show resistance to apoptosis induced by bortezomib and G5, but they are more susceptible to necrosis induced by G5. Conversely, T98G cells are more susceptible to apoptosis induced by both inhibitors but show some resistance to G5-induced necrosis. No overt differences in the induction of Noxa and Mcl-1 or in the expression levels of other components of the apoptotic machinery were observed between U87MG and T98G cells. Instead, by comparing the transcriptional profiles of the two cell lines, we have found that the resistance to G5-induced necrosis could arise from differences in glutathione synthesis/utilization and in the microenvironment. In particular, collagen IV, which is highly expressed in T98G cells, and fibronectin, whose adhesive function is counteracted by tenascin-C in U87MG cells, can restrain the necrotic response to G5. Collectively, our results provide an initial characterization of the molecular signals governing cell death by necrosis in glioblastoma cell lines.

A Receptor-interacting Protein 1 (RIP1)-independent Necrotic Death under the Control of Protein Phosphatase PP2A That Involves the Reorganization of Actin Cytoskeleton and the Action of Cofilin-1

“…On the other side G5 treatment induces profound changes in cell spreading and actin cytoskeleton (18,22) as exemplified in Fig. 6A.…”

“…U87MG cells expressing Bcl-xL, Drp1 K38A, GFP, Cofilin constructs, and myristoylated Akt were generated by retroviral infection (18). In all trypan blue exclusion assays, at least 400 cells from three independent samples were counted.…”

“…Isopeptidase Inhibitor G5 and the Redox Cycling Quinone, DMNQ-To explore the existence of different necrotic signaling pathways, we used two different chemical stressors: the isopeptidases inhibitor G5, an inducer of alterations in cell adhesion and actin cytoskeleton (18,21,22), and DMNQ, a generator of reactive oxygen species at mitochondrial level (23).…”

“…As the cellular model to study necrosis we selected U87MG glioblastoma cells because of their intrinsic resistance to apoptosis and the tendency to die by necrosis (18). In addition, we overexpressed Bcl-xL to further suppress apoptosis.…”

The DeISGylase USP18 limits TRAIL-induced apoptosis through the regulation of TRAIL levels

“…30 Hence, they represent a good model to investigate the synergisms between TRAIL ad the IFN signaling. To evaluate the effect of the IFN-α treatment on apoptosis responsiveness to TRAIL, T98G cells were treated with IFN-α and next incubated with increasing amounts of rhTRAIL.…”