Abstract A006: Skp2 associates with Slug and androgen receptor in aggressive prostate cancer

Abstract

Abstract Introduction: The Skp2 F-box protein is the substrate recruiting component of the SCF (Skp1-Cullin 1-F-box) type of E3 ubiquitin-ligase complexes. Skp2 plays an important role in prostate tumorigenesis (e.g., via recently reported stabilization of EZH2 or Twist1), which needs further elucidation. Patients and Methods: Prostate cancer patient cohort (N=101) was analyzed by immunohistochemistry for the following proteins: Skp2, AR, Ki-67, Slug, E-cadherin, MdmX, Mdm2, and p53. The indicated proteins were also analyzed in seminal vesicles and lymph node metastases (SV=35 and LN=18 patients, respectively), as well as in benign prostatic hyperplasia (BPH=34). Colocalization analysis was performed using Perkin Elmer Opal Multiplex kit, Vectra 3.0 imaging system, and confocal microscope Carl Zeiss LSM 780. Independent prostate cancer cohort (N=30) was evaluated for TMPRSS2-ERG fusion by a triple-color deletion assay and assessed for Skp2, ERG, and NQO1 protein expression. Cox regression analysis and Kaplan-Meier curves were used to assess importance of Skp2, Slug, EZH2, and Twist1 for biochemical relapse in the TCGA prostate cancer dataset (N=488, RNA seq). Results: Expression of E-cadherin was lower in primary prostate cancer and seminal vesicles compared to BPH and LN, which may be linked to epithelial-mesenchymal transition. Opposite expression profile was observed for Skp2, MdmX, and Slug. High Gleason score (≥8, N=30) was significantly associated with higher Skp2 and lower E-cadherin expression (p<0.001 and 0.011, respectively). Skp2 slightly correlated with AR and Slug in the whole patient cohort (Rs 0.37 and 0.322, respectively). These correlations were stronger in patients with high Gleason score (Rs 0.53 and 0.56, respectively). In patients with metastasis into lymph nodes, Skp2 similarly correlated with Slug and AR (Rs 0.56 and 0.37, respectively) while androgen receptor further correlated with Ki-67 (Rs 0.50). Confocal microscopy revealed colocalization of Skp2 and Slug in prostate cancer cells. In an independent cohort, Skp2 correlated with expression of ERG, NQO1, and percentage of cancer cells positive for TMPRSS2-ERG (Rs 0.503, 0.387 and 0.615, respectively). In the TCGA dataset, high mRNA levels of Skp2 and EZH2 (but not Slug or Twist1) associated with shorter time to biochemical relapse, compared to low mRNA levels [HR 3.62 (2.1 – 6.23), p<0.001]. Conclusion: Immunohistochemistry and colocalization studies revealed association between Skp2 and Slug in aggressive prostate cancer. Other factors such as TMPRSS2-ERG fusion or oxidative stress may contribute to prostate cancer progression. Citation Format: Jan Bouchal, Gvantsa Kharaishvili, Alena Mickova, Mariam Gachechiladze, Alena Burdova, Martin Mistrik, Milan Kral, Balazs Gyorffy, Zdenek Kolar. Skp2 associates with Slug and androgen receptor in aggressive prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A006.