USP17 regulates cell proliferation by deubiquitinating and inhibiting RCE1, which influences the localization and activation of the small GTPases NRAS and HRAS (Burrows et al. 2009). In addition, USP17 mediates deubiquitination of CDC25A, which prevents CDC25A degradation by the proteasome during the G1/S and G2/M phases, promoting cell-cycle progression (Pereq et al. 2010). USP17 cleaves Lys-48 and Lys-63-linked polyubiquitin chains from the cytoplasmic innate immune receptors DDX58 (RIG-I) and IFIH1 (MDA5), which increases activation of the IFN-beta promoter, part of the cellular response to viral infection (Chen et al. 2010). USP17 expression is upregulated by interleukin-4 and interleukin-6 (Burrows et al. 2004).