Abstract 181A: PIN1 and FOXP3 regulate SKP2 expression

Abstract

S-phase kinase-associated protein 2 (SKP2), a component of the E3 ubiquitin ligase SKP1-CUL1-Fbox complex, acts as an oncogene/oncoprotein as evidence suggests that overexpression of SKP2 results in cell cycle dysregulation and tumorigenesis as well as associates with poor prognosis in numerous cancers. The unique peptidyl-propyl isomerase PIN1, which isomerizes the cis-trans peptide bond between pSer/pThr and proline, regulates its target proteins’ cell localization, stability, and function. However, whether SKP2 is the target protein of PIN1 remains unknown. Herein, we demonstrate that SKP2 expression is regulated by PIN1 and FOXP3. First, we observed that knock-down PIN1 using siRNAs reduced SKP2 protein level in several cancer cell lines (MCF7, PC3, DU145, HepG2, and JEG3 cells). Secondly, we found that overexpression of PIN1 increased SKP2 protein level. Furthermore, PIN1 dose-dependently enhanced SKP2 promoter activity in gene reporter assay. Since FOXP3 is a known transcriptional repressor for the oncogene SKP2, we investigated whether PIN1 affects FOXP3-mediated SKP2 expression. Interestingly, we observed that PIN1 dose-dependently counteracted FOXP3-mediated SKP2 promoter activity. Finally, we demonstrated that mutations on PIN1 (W34A) and FOXP3 (Y342F) abolished PIN1-mediated and FOXP3-mediated SKP2 expression, respectively. Taken together, our results suggest that PIN1 functions as a novel regulator of SKP2 and with FOXP3 may be involved in tumor development and progression. Citation Format: Wei-Hsiung Yang, Chiung-Min Wang, William H. Yang. PIN1 and FOXP3 regulate SKP2 expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 181A.