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.

Interferon-stimulated gene 15 induces cancer cell death by suppressing the NF-κB signaling pathway

“…These results thus indicated that ISG15 and USP18 were induced by anti-cancer agents in blood cancer cells. Notably, these results were consistent with previous studies [11, 12], in which ISG15 was significantly induced by classic anti-cancer camptothecin [11] and all-trans retinoic acid [12]. …”

“…These findings is consistent with previous studies in which all-trans-retinoic acid (RA) promotes the transcription of ISG15, USP18, and ISGylation activating enzyme UBE1L in RA-sensitive but not resistant leukemia cells [12]. ISG15 was also induced by classic anti-cancer agent camptothecin [11]. This study along with these previous studies thus suggest that in contrast to promoting tumorigenesis, ISG15 also displays anti-cancer activities.…”

Modulation of the Host Interferon Response and ISGylation Pathway by B. pertussis Filamentous Hemagglutinin

“…However, our data suggest that FHA might also stimulate expression of these two genes through a mechanism independent of IFN-α, similar to the genotoxic agent, camptothecin which activates ISG15 expression in a p53-dependent, and IFN- and Jak-Stat-independent manner [44]. Two arguments support this hypothesis.…”

ISG15 in the tumorigenesis and treatment of cancer: An emerging role in malignancies of the digestive system

“…Camptothecin has been shown to induce the expression of ISG15 in human fibrosarcoma cells [160], which suggests that ISG15 can function as a tumor suppressor. Matsumura et al [161] found that 5-fluorouracil (5-FU) stimulated IFN-mediated signaling pathways in three human ESCC cell lines, which included the upregulation of ISG15 in both the presence and absence of type I IFNs, and reported that IFN-α/β augmented the suppressive effects of 5-FU on ESCC cell growth.…”