title: Inhibitors of ubiquitin-activating enzyme (E1), a new class of potential cancer therapeutics.
abstract: The conjugation of proteins with ubiquitin plays numerous regulatory roles through both proteasomal-dependent and nonproteasomal-dependent functions. Alterations in ubiquitylation are observed in a wide range of pathologic conditions, including numerous malignancies. For this reason, there is great interest in targeting the ubiquitin-proteasome system in cancer. Several classes of proteasome inhibitors, which block degradation of ubiquitylated proteins, are widely used in research, and one, Bortezomib, is now in clinical use. Despite the well-defined and central role of the ubiquitin-activating enzyme (E1), no cell permeable inhibitors of E1 have been identified. Such inhibitors should, in principle, block all functions of ubiquitylation. We now report 4[4-(5-nitro-furan-2-ylmethylene)-3,5-dioxo-pyrazolidin-1-yl]-benzoic acid ethyl ester (PYR-41) as the first such inhibitor. Unexpectedly, in addition to blocking ubiquitylation, PYR-41 increased total sumoylation in cells. The molecular basis for this is unknown; however, increased sumoylation was also observed in cells harboring temperature-sensitive E1. Functionally, PYR-41 attenuates cytokine-mediated nuclear factor-kappaB activation. This correlates with inhibition of nonproteasomal (Lys-63) ubiquitylation of TRAF6, which is essential to IkappaB kinase activation. PYR-41 also prevents the downstream ubiquitylation and proteasomal degradation of IkappaBalpha. Furthermore, PYR-41 inhibits degradation of p53 and activates the transcriptional activity of this tumor suppressor. Consistent with this, it differentially kills transformed p53-expressing cells. Thus, PYR-41 and related pyrazones provide proof of principle for the capacity to differentially kill transformed cells, suggesting the potential for E1 inhibitors as therapeutics in cancer. These inhibitors can also be valuable tools for studying ubiquitylation.
authors.affiliation: Laboratory of Protein Dynamics and Signaling, Center for Cancer Research, National Cancer Institute at Frederick, NIH, Frederick, Maryland 21702, USA. yangyili@ncifcrf.gov
authors.forename: Yili
authors.initials: Y
authors.lastname: Yang
authors.forename: Jirouta
authors.initials: J
authors.lastname: Kitagaki
authors.forename: Ren-Ming
authors.initials: RM
authors.lastname: Dai
authors.forename: Yien Che
authors.initials: YC
authors.lastname: Tsai
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Lorick
authors.forename: Robert L
authors.initials: RL
authors.lastname: Ludwig
authors.forename: Shervon A
authors.initials: SA
authors.lastname: Pierre
authors.forename: Jane P
authors.initials: JP
authors.lastname: Jensen
authors.forename: Ilia V
authors.initials: IV
authors.lastname: Davydov
authors.forename: Pankaj
authors.initials: P
authors.lastname: Oberoi
authors.forename: Chou-Chi H
authors.initials: CC
authors.lastname: Li
authors.forename: John H
authors.initials: JH
authors.lastname: Kenten
authors.forename: John A
authors.initials: JA
authors.lastname: Beutler
authors.forename: Karen H
authors.initials: KH
authors.lastname: Vousden
authors.forename: Allan M
authors.initials: AM
authors.lastname: Weissman
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001565:Benzoates / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D005663:Furans / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D019169:Jurkat Cells; D051379:Mice; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011720:Pyrazoles / Q000494:pharmacology*; D011817:Rabbits; D013379:Substrate Specificity; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C523934:4(4-(5-nitro-furan-2-ylmethylene)-3,5-dioxo-pyrazolidin-1-yl)-benzoic acid ethyl ester; D001565:Benzoates; D016207:Cytokines; D005663:Furans; D016328:NF-kappa B; D061988:Proteasome Inhibitors; D011720:Pyrazoles; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D051550:I-kappa B Kinase; D046988:Proteasome Endopeptidase Complex; D044764:Ubiquitin-Activating Enzymes