Tumor necrosis factor related apoptosis inducing ligand (TRAIL) regulates deubiquitinase USP5 in tumor cells

Harish Potu,Nicholas J Donato,Malathi Kandarpa,Moshe Talpaz,Luke F Peterson

doi:10.18632/oncotarget.27196

Abstract

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway has emerged as a cancer therapeutic target. However, clinical trials have proven that most human cancers are resistant to TRAIL. We show that exposure to recombinant TRAIL resulted in the accumulation of ubiquitinated proteins and free ubiquitin polymers, suggesting a link between TRAIL and the ubiquitin (Ub)-proteasome pathway. TRAIL treatment in cancer cells reduced the activity and cleavage of USP5, a deubiquitinase (DUB) previously shown to target unanchored Ub polymers and regulate p53-mediated transcription. TRAIL was effective in suppressing USP5 activity and cleavage in TRAIL-sensitive cells but not resistant cells. Knockdown of USP5 in TRAIL-resistant cells demonstrated that USP5 controls apoptotic responsiveness to TRAIL. USP5 cleavage and ubiquitination were blocked by caspase-8 specific inhibitors. A small-molecule USP5/9× inhibitor (G9) combined with TRAIL enhanced apoptosis and blocked colony growth in highly TRAIL-resistant cell lines. Finally, USP5 protein levels and activity were found to be frequently deregulated in TRAIL-resistant cells. Together, we conclude that activated TRAIL enhances USP5 activity and induces apoptosis in TRAIL-sensitive and -resistant cells. We also suggest that USP5 inhibition may be effective in inducing apoptotic thresholds to enhance responsiveness to TRAIL.

Highlights

Tumor necrosis factor (TNF)-related apoptosisinducing ligand (TRAIL) appears to be a promising candidate for cancer therapeutics because of its selective cytotoxic effect on cancer cells while sparing normal cells [1,2,3]
We further assessed if this ubiquitination profile is evident in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-sensitive and -resistant pancreatic, breast and glioblastoma cell lines (Figure 1B)
TRAIL is selectively cytotoxic to cancer cells and is an attractive candidate for specific targeting of cancer cells while sparing normal cells

Summary

Introduction

Tumor necrosis factor (TNF)-related apoptosisinducing ligand (TRAIL) appears to be a promising candidate for cancer therapeutics because of its selective cytotoxic effect on cancer cells while sparing normal cells [1,2,3]. TRAIL induces apoptosis by binding to two death receptors DR-4 (TRAIL-R1) and DR-5 (TRAIL-R2) This leads to the recruitment of the adaptor protein, Fasassociated death domain (FADD), which in turn recruits the initiator caspase, caspase-8, resulting in the formation of the death-inducing signaling complex (DISC). The Ubiquitin proteasome system leads to the degradation of the ubiquitinated proteins Proteasome inhibitors such as bortezomib could dramatically sensitize multiple myeloma cells [13], and a variety of human and mouse solid tumor cells to the apoptotic effects of TRAIL [13, 14]. Other ubiquitin ligases control the www.oncotarget.com apoptosis pathway such as, A20 E3 ligase mediates RIP1 ubiquitination through a K63-linked polyubiquitin chain that binds caspase-8 and inhibits TRAIL-induced apoptosis in human glioblastoma [15]. Caspase-8 ubiquitination at its C-terminus by a CUL3-based E3 ligase complex promotes caspase-8 activation and apoptosis [18]

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Conclusion