Ubiquitin C-Terminal Hydrolase-L1 Potentiates Cancer Chemosensitivity by Stabilizing NOXA

Abstract

The BH3-only protein NOXA represents one of the critical mediators of DNA-damage-induced cell death. In particular, its involvement in cellular responses to cancer chemotherapy is increasingly evident. Here, we identify a strategy of cancer cells to escape genotoxic chemotherapy by increasing proteasomal degradation of NOXA. We show that the deubiquitylating enzyme UCH-L1 is a key regulator of NOXA turnover, which protects NOXA from proteasomal degradation by removing Lys(48)-linked polyubiquitin chains. In the majority of tumors from patients with melanoma or colorectal cancer suffering from high rates of chemoresistance, NOXA fails to accumulate because UCH-L1 expression is epigenetically silenced. Whereas UCH-L1/NOXA-positive tumor samples exhibit increased sensitivity to genotoxic chemotherapy, downregulation of UCH-L1 or inhibition of its deubiquitylase activity resulted in reduced NOXA stability and resistance to genotoxic chemotherapy in both human and C. elegans cells. Our data identify the UCH-L1/NOXA interaction as a therapeutic target for overcoming cancer chemoresistance.

Regulation of the DNA damage response by ubiquitin conjugation

“…The transcriptional upregulation of these pro-apoptotic members in response to DNA damage however may not suffice the required pro-apoptotic trigger toward MOMP as this process is tightly regulated by a number of other Bcl-2 members and only the ultimate pro-apoptotic composition of these proteins can efficiently induce cell death (Ni Chonghaile and Letai, 2008). Accordingly, the genes of some BH3-only proteins appear to be constitutively transcribed in cancer cells as reported for BIK or NOXA (Hur et al, 2004; Brinkmann et al, 2013; Dengler et al, 2014). The majority of these cells however resist apoptosis suggesting that the imbalance in Bcl-2 protein family members (e.g., upregulation of anti-apoptotic members or downregulation of BAX/BAK) efficiently counter the pro-apoptotic action of these factors.…”

“…Strikingly, the expression levels of a number of Bcl-2 protein family members including NOXA (Qin et al, 2005; Brinkmann et al, 2013), MCL-1 (Adams and Cory, 2007), A1 (Kucharczak et al, 2005), BCL-2 (Dimmeler et al, 1999), BAK (Qin et al, 2005), BIK (Marshansky et al, 2001; Hur et al, 2004), BIM (Nikrad et al, 2005) was altered when the proteasome was inhibited indicating an essential role of the UPS in regulating Bcl-2-family protein abundance. However, a direct regulation of Bcl-2-protein level via the UPS has only been reported for BAX (Chang et al, 1998; Li and Dou, 2000), BIM (Akiyama et al, 2003), BCL-2 (Dornan et al, 2004b), NOXA (Brinkmann et al, 2013), MCL-1 (Zhong et al, 2005), A1 (Kucharczak et al, 2005), and BCL-B (van de Kooij et al, 2013), while the identities of the responsible E3 ligases and DUBs are largely unknown with some exceptions (Tables 1, 2). …”

“…In particular, ubiquitylation of NOXA has recently been shown to be involved in the regulation of NOXA protein turn-over and thereby influences cellular stress responses (Baou et al, 2010; Dengler et al, 2014). Interfering with this process, dysregulation of NOXA ubiquitylation has been shown to be an efficient strategy of some tumor cells in order to resist the genotoxic chemotherapy (Brinkmann et al, 2013). Specifically, these data showed that NOXA was strongly ubiquitylated in some tumor samples.…”

Cyclin D1-CDK4 activity drives sensitivity to bortezomib in mantle cell lymphoma by blocking autophagy-mediated proteolysis of NOXA

“…However, the predominant mechanism by which NOXA protein is enhanced seems to be protein stabilization by targeting the rapid NOXA protein turnover both in MCL and in melanoma cells [24, 36]. To uncover the mechanism by which CDK4 inhibition diminishes NOXA protein in bortezomib-treated cells, we first quantified NOXA RNA levels.…”

“…The only reported polyubiquitin chains for NOXA are K11 or K48 linkages [36, 66]. Although the K63 linkage has been shown to direct proteins preferentially towards autophagy instead of proteasomal degradation, all ubiquitin linkages including K11 and K48 have been shown to be involved in autophagosomal trafficking [67, 68].…”