The isopeptidase inhibitor 2cPE triggers proteotoxic stress and ATM activation in chronic lymphocytic leukemia cells

Abstract

Relapse after treatment is a common and unresolved problem for patients suffering of the B-cell chronic lymphocytic leukemia (B-CLL). Here we investigated the ability of the isopeptidase inhibitor 2cPE to trigger apoptosis in leukemia cells in comparison with bortezomib, another inhibitor of the ubiquitin-proteasome system (UPS). Both inhibitors trigger apoptosis in CLL B cells and gene expression profiles studies denoted how a substantial part of genes up-regulated by these compounds are elements of adaptive responses, aimed to sustain cell survival. 2cPE treatment elicits the up-regulation of chaperones, proteasomal subunits and elements of the anti-oxidant response. Selective inhibition of these responses augments apoptosis in response to 2cPE treatment. We have also observed that the product of the ataxia telangiectasia mutated gene (ATM) is activated in 2cPE treated cells. Stimulation of ATM signaling is possibly dependent on the alteration of the redox homeostasis. Importantly ATM inhibition, mutations or down-modulation increase cell death in response to 2cPE. Overall this work suggests that 2cPE could offer new opportunities for the treatment of B-CLL.

GSK3β is a key regulator of the ROS-dependent necrotic death induced by the quinone DMNQ

“…G5 triggers pleiotropic stresses, which can drive cells to death through different pathways. Proteasome impairment, misfolding and proteotoxic stress, oxidative stress and cytoskeletal malfunctions are all hallmarks of the G5induced cell death [11][12][13][14] . The partial impact of GSK3β could stem from the co-existence of these multiple pathways.…”

“…Since GSK3β can be involved in regulating ROS-induced cell death [32][33][34][35] , we hypothesized that its involvement in G5-induced death could depend on the ability of the compound of triggering oxidative stress. The impact of G5 on oxidative stress could be direct, through the depletion of glutathione or indirect, through the induction of protein misfolding 14 . To prove this hypothesis, we selected the redox-cycling 2,3-dimethoxy-1,4naphthoquinone (DMNQ), a well-known inducer of oxidative stress.…”

“…G5 is a non-selective isopeptidases inhibitor that can react with cellular thiols, thus eliciting multiple cellular stresses [10][11][12][13][14][15] . G5 belongs to a family of compounds that have been synthetized and investigated for the ability to commend accidental death in cancer cells, with therapeutic perspectives [16][17][18][19][20][21][22] .…”

“…Protein misfolding, ER-stress, deubiquitinases inhibition and accumulation of polyubiquitylated proteins, glutathione depletion, alterations of the actin cytoskeleton and of the cell adhesion mark the cellular response to G5. In cells resistant to apoptosis this plethora of stresses can result in a necrotic death, which is distinguishable from necroptosis 11,13,14 . However, few additional data are available about the signaling networks transducing this peculiar form of necrosis.…”

“…For this reason, we conducted a functional shRNAbased screening aimed to identify genes that can influence cell survival in response to this compound. We used as a model the glioblastoma cell line U87MG, which activates necrosis when treated with high doses of G5 12,14 .…”