Camptothecin induces the ubiquitin-like protein, ISG15, and enhances ISG15 conjugation in response to interferon

J Interferon Cytokine Res. 2004 Nov;24(11):647-54. doi: 10.1089/jir.2004.24.647.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Blotting, Northern
  • Blotting, Western
  • Camptothecin / pharmacology*
  • Cell Line, Tumor
  • Cell Nucleus / metabolism
  • Cycloheximide / pharmacology
  • Cytokines / biosynthesis*
  • Cytokines / chemistry
  • Dose-Response Relationship, Drug
  • Humans
  • Interferons / metabolism*
  • Protein Binding
  • Protein Processing, Post-Translational
  • RNA, Messenger / metabolism
  • Signal Transduction
  • Time Factors
  • Topoisomerase I Inhibitors
  • Ubiquitins / biosynthesis*
  • Ubiquitins / chemistry


  • Antineoplastic Agents, Phytogenic
  • Cytokines
  • RNA, Messenger
  • Topoisomerase I Inhibitors
  • Ubiquitins
  • ISG15 protein, human
  • Interferons
  • Cycloheximide
  • Camptothecin