Loss of function mutations in Kelch Like ECH Associated Protein 1 (KEAP1) or gain-of-function mutations in nuclear factor erythroid 2-related factor 2 (NRF2) are common in non-small cell lung cancer (NSCLC) and is associated with therapeutic resistance. To discover novel NRF2 inhibitors for targeted therapy, we conducted a quantitative high-throughput screen using a diverse set of ~400,000 small molecules (Molecular Libraries Small Molecule Repository Library, MLSMR) at the National Center for Advancing Translational Sciences. We identified ML385 as a probe molecule that binds to NRF2 and inhibits its downstream target gene expression. Specifically, ML385 binds to the Neh1, the Cap ‘N’ Collar Basic Leucine Zipper (CNC-bZIP) domain of NRF2, and interferes with the binding of the V-Maf Avian Musculoaponeurotic Fibrosarcoma Oncogene Homolog G (MAFG)-NRF2 protein complex to regulatory DNA binding sequences. In clonogenic assays, when used in combination with platinum-based drugs such as doxorubicin or taxol, ML385 substantially enhances cytotoxicity in NSCLC cells compared to single agents alone. ML385 shows specificity and selectivity for NSCLC cells with KEAP1 mutation leading to gain of NRF2 function. In preclinical models of NSCLC with gain of NRF2 function, ML385 in combination with carboplatin showed significant anti-tumor activity. We demonstrate the discovery and validation of ML385 as a novel and specific NRF2 inhibitor and conclude that targeting NRF2 may represent a promising strategy for the treatment of advanced NSCLC.

Ubiquitin-dependent proteolysis plays an essential role in the regulation of a variety of cellular processes, including cell proliferation, differentiation, and apoptosis (1-3). Ubiquitin (Ub) 3 is covalently attached to target proteins by a cascade enzyme system consisting of Ub-activating (E1), conjugating (E2), and ligating (E3) enzymes (1, 4). Ub E3 ligases that confer the substrate specificity have been grouped into two families; the HECT-domain family that is defined by its homology to E6-associated protein (E6AP) and the RING family carrying RING-finger domain that is essential for the Ub ligase activity (5, 6). One of the well defined RING E3 ligases is the Skp1/Cul1/F-box protein complex, in which Cul1 serves as a scaffold molecule that interacts with Skp1 and a small RING-finger protein Roc1, also known as Hrt1 and Rbx1 (7-9). F-box proteins are recruited to the complex by binding to the Skp1 adaptor protein.At least six Cul members have been identified: Cul1, Cul2, Cul3, Cul4A, Cul4B, and Cul5 (10). Of these, Cul3 is known to mediate the degradation of several proteins, such as cyclin E (11), but the molecular composition of Cul3-based Ub ligase was unknown. Recently, a large family of proteins having BTB (Bric-a-brac/Tramtrack/Broad complex) domain has been identified as novel Cul3-interacting proteins (12). Most BTB proteins, but not all, have additional domains for proteinprotein interaction, such as zinc fingers, Kelch repeats, and MATH motifs. Furthermore, a subset of proteins containing BTB domain has been identified to function as substrate-specific adaptors that bind to Cul3. Specifically, MEL-26, a homolog of human SPOP (speckle-type POZ protein) in Caenorhabditis elegans, was first identified as a BTB protein that serves as a specific adaptor of MEI-1 for the ubiquitination by Cul3-based Ub ligase and subsequent degradation by the proteasome (13). MEI-1 is a subunit of the katanin-like microtubule severing heterodimer MEI-1/MEI-2 that localizes to the spindles and the chromosomes during meiosis (14). SPOP BTB protein has also been shown to mediate the ubiquitination of the Polycomb group BMI and the variant histone MacroH2A (15). In addition, Keap1 BTB protein was shown to recruit Nrf2 to . Nrf2 is a transcription factor that regulates the expression of anti-oxidant genes upon oxidative stress. In Schizosaccharomyces pombe, Btb1p, Btb2p, and Btb3p interact with Cul3, but their functions remain unknown (20). Therefore, so far only a few protein substrates have been shown to interact with BTB proteins for their ubiquitination by Cul3-based Ub ligases.Daxx was originally identified as a protein that binds to the death domain of Fas receptor by yeast two-hybrid screening (21). Daxx interacts with the apoptosis signal-regulating kinase 1 (ASK1) and promotes Fas-mediated apoptosis through the activation of Jun N-terminal kinase (22). Subsequent studies have also shown that Daxx behaves as a proapoptotic protein under various stress conditions (21,(23)(24)(25). On the contrary, homozygous deletio...

Identification of the cellular mechanisms that mediate cancer cell chemosensitivity is important for developing new cancer treatment strategies. Several chemotherapeutic drugs increase levels of the posttranslational modifier ISG15, which suggests that ISGylation could suppress oncogenesis. However, how ISGylation of specific target proteins controls tumorigenesis is unknown. Here, we identified proteins that are ISGylated in response to chemotherapy. Treatment of a human mammary epithelial cell line with doxorubicin resulted in ISGylation of the p53 family protein p63. An alternative splice variant of p63, ΔNp63α, suppressed the transactivity of other p53 family members, and its expression was abnormally elevated in various human epithelial tumors, suggestive of an oncogenic role for this variant. We showed that ISGylation played an essential role in the downregulation of ΔNp63α. Anticancer drugs, including doxorubicin, induced ΔNp63α ISGylation and caspase-2 activation, leading to cleavage of ISGylated ΔNp63α in the nucleus and subsequent release of its inhibitory domain to the cytoplasm. ISGylation ablated the ability of ΔNp63α to promote anchorageindependent cell growth and tumor formation in vivo as well to suppress the transactivities of proapoptotic p53 family members. These findings establish ISG15 as a tumor suppressor via its conjugation to ΔNp63α and provide a molecular rationale for therapeutic use of doxorubicin against ΔNp63α-mediated cancers.

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DBC1 is a major inhibitor of SIRT1, which plays critical roles in the control of diverse cellular processes, including stress response and energy metabolism. Therefore, the DBC1-SIRT1 interaction should finely be regulated. Here we report that DBC1 modification by Small Ubiquitin-like Modifier 2/3 (SUMO 2/3), but not by SUMO1, is crucial for p53 transactivation under genotoxic stress. Whereas etoposide treatment reduced the interaction of DBC1 with SENP1, it promoted that with PIAS3, resulting in an increase in DBC1 sumoylation. Remarkably, the switching from SENP1 to PIAS3 for DBC1 binding was achieved by ATM/ATR-mediated phosphorylation of DBC1. Furthermore, DBC1 sumoylation caused an increase in the DBC1-SIRT1 interaction, leading to the release of p53 from SIRT1 for transcriptional activation. Consistently, SENP1 knockdown promoted etoposide-induced apoptosis, whereas knockdown of PIAS3 or SUMO2/3 and overexpression of sumoylationdeficient DBC1 mutant inhibited it. These results establish the role of DBC1 sumoylation in the promotion of p53-mediated apoptosis in response to genotoxic stress.

Katanin is a heterodimeric enzyme that severs and disassembles microtubules. While the p60 subunit has the enzyme activity, the p80 subunit regulates the p60 activity. The microtubule-severing activity of katanin plays an essential role in axonal growth. However, the mechanisms by which neuronal cells regulate the expression of katanin-p60 remains unknown. Here we showed that USP47 and C terminus of Hsp70-interacting protein (CHIP) antagonistically regulate the stability of katanin-p60 and thereby axonal growth. USP47 was identified as a katanin-p60-specific deubiquitinating enzyme for its stabilization. We also identified CHIP as a ubiquitin E3 ligase that promotes proteasome-mediated degradation of katanin-p60. Moreover, USP47 promoted axonal growth of cultured rat hippocampal neurons, whereas CHIP inhibited it. Significantly, treatment with basic fibroblast growth factor (bFGF), an inducer of axonal growth, increased the levels of USP47 and katanin-p60, but not CHIP. Consistently, bFGF treatment resulted in a marked decrease in the level of ubiquitinated katanin-p60 and thereby in the promotion of axonal growth. On the other hand, the level of USP47, but not CHIP, decreased concurrently with that of katanin-p60 as axons reached their target cells. These results indicate that USP47 plays a crucial role in the control of axonal growth during neuronal development by antagonizing CHIP-mediated katanin-p60 degradation.

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Under normal conditions, apoptosis inducing factor (AIF) in the mitochondrial membrane functions as an oxidoreductase that scavenges reactive oxygen species. Under certain stresses, such as exposure to N‐methyl‐N′‐nitro‐N′‐nitrosoguanidine (MNNG), AIF is truncated from the mitochondria and translocated to the nucleus, where it induces caspase‐independent programmed cell death, featured by chromatin condensation and large‐scale DNA breakage. Here we demonstrate that USP2 deubiquitinates AIF whereas CHIP functions as an ubiquitin E3 ligase of AIF, thus controlling the stability of AIF. Expression of USP2 resulted in acceleration of AIF‐mediated apoptotic process in HeLa cells, whereas that of CHIP attenuates it. Consistently, CHIP−/− mouse embryonic fibroblast (MEF) cells showed an increased sensitivity to MNNG. Collectively, these results indicate that CHIP and USP2 display antagonistic roles in the regulation of AIF‐mediated, caspase‐independent apoptosis.