title: Camptothecin induces the ubiquitin-like protein, ISG15, and enhances ISG15 conjugation in response to interferon.
abstract: Interferon (IFN)-stimulated gene (15 kDa) (ISG15) is a ubiquitin-like protein that forms covalent conjugates with cellular proteins. ISG15 is induced by IFN, microbial challenge, and p53, suggesting that it represents a genetic response that is shared among diverse stress stimuli. To investigate the regulation of this posttranslational modification pathway by a genotoxic chemotherapeutic agent, we examined ISG15 induction and conjugation in cells treated with the topoisomerase I (topoI) poison, camptothecin (CPT). CPT induced ISG15mRNA, and induction required protein synthesis and a functional p53 protein. However, IFN and the Jak-Stat components of the IFN signaling pathway were dispensable for CPT induction of ISG15. CPT induced free ISG15 and conjugates in a dose-dependent and time-dependent manner. A single 55-kDa protein was the prominent CPT-induced ISG15 conjugate and localized to the nuclear compartment. CPT-induced ISG15 conjugates were distinct from those induced by IFN; however, CPT treatment dramatically enhanced ISG15 conjugation in response to IFN. These findings provide the first evidence of a stimulus-specific induction of discrete ISG15 conjugate species and demonstrate that treatment with a combination of cancer therapeutic agents can cooperate to enhance ISG15 conjugation. Identification of the specific ISG15 conjugates induced by chemotherapeutic agents may reveal novel molecular targets.
authors.affiliation: Program in Molecular and Cell Biology, University of Maryland, School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Mingjuan
authors.initials: M
authors.lastname: Liu
authors.forename: B Timothy
authors.initials: BT
authors.lastname: Hummer
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Li
authors.forename: Bret A
authors.initials: BA
authors.lastname: Hassel
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D015152:Blotting, Northern; D015153:Blotting, Western; D002166:Camptothecin / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D016207:Cytokines / Q000096:biosynthesis* / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007372:Interferons / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D059004:Topoisomerase I Inhibitors; D014452:Ubiquitins / Q000096:biosynthesis* / Q000737:chemistry
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D016207:Cytokines; D012333:RNA, Messenger; D059004:Topoisomerase I Inhibitors; D014452:Ubiquitins; C074034:ISG15 protein, human; D007372:Interferons; D003513:Cycloheximide; D002166:Camptothecin