Abstract 24: Loss of ubiquitin-specific peptidase 18 (USP18) causes cold sensitive mice by destabilizing the critical regulator of thermogenesis: uncoupling protein-1 (UCP-1)

Abstract

Abstract USP18 is the major ISG15 (Interferon-Stimulated Gene 15) deconjugase that removes ISG15 from substrate proteins. We recently reported that USP18 null mice spontaneously develop leiomyosarcomas. Intriguingly, these USP18 null mice are also markedly cold sensitive as compared to their wild-type littermates. When briefly exposed to cold stimuli, USP18 null mice significantly (P < 0.05) decreased their body temperature. In contrast, wild-type mice exposed to the same experimental conditions exhibited transient changes in their body temperature. We sought to elucidate the engaged mechanism. Expression profiles of critical thermogenic regulatory proteins were examined by immunoblot analyses of brown fat tissues of USP18 null mice. Strikingly, UCP-1 expression was substantially reduced in these tissues of USP18 null versus wild-type mice. To independently confirm that reduced UCP-1 expression was caused by loss of USP18, stable knock-down of USP18 was independently achieved in a panel of murine cell lines by use of transfected small hairpin RNAs (shRNAs). The obtained results were compared to that of transfected control vectors. USP18 down-regulation by different shRNAs markedly reduced UCP-1 protein as compared to controls. As expected, engineered gain of USP18 expression in the same murine cell lines stabilized UCP-1 protein. We explored if UCP-1 destabilization was due to its complex formation with the ubiquitin-like protein ISG15. This was the expected experimental outcome since USP18 is the distinct deconjugase that removes ISG15 from complexed proteins. Immunoprecipitation assays were performed to establish this direct association. These studies revealed a complex formed between ISG15 and UCP-1 protein. Thus, engineered loss of USP18 in mice led to cold sensitive mice from repression of UCP-1. As a consequence of its complex with ISG15, the thermogenic regulator UCP-1 was destabilized. Taken together, this study extends prior work by showing a previously unrecognized link between USP18 and regulation of thermogenesis. This defines a novel role for the USP18 protease in metabolism. Citation Format: Xi Liu, Yun Lu, Lin Zheng, David J. Sekula, Sarah J. Freemantle, Ethan Dmitrovsky. Loss of ubiquitin-specific peptidase 18 (USP18) causes cold sensitive mice by destabilizing the critical regulator of thermogenesis: uncoupling protein-1 (UCP-1). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 24.