Skp2 regulates androgen receptor through ubiquitin-mediated degradation independent of Akt/mTOR pathways in prostate cancer.

The intervention of advanced prostate cancer (PCa) in patients has been commonly depending on androgen deprivation therapy. Despite of tremendous research efforts, however, molecular mechanisms on AR regulation remain poorly understood, particularly for castration resistant prostate cancer (CRPC). Targeting AR and associated factors is considered an effective strategy in PCa treatment. Human prostate cancer cells were used in this study. Manipulations of Skp2 expression were achieved by Skp2 shRNA/siRNA or overexpression of plasmids. Dual luciferase reporter assay was applied for AR activity assessment. Western blot, ubiquitination assay, immunoprecipitation, and immunofluorescence were applied to detect the proteins. Our results demonstrated that Skp2 directly involves the regulation of AR expression through ubiquitination-mediated degradation. Skp2 interacted with AR protein in PCa cells, and enforced expression of Skp2 resulted in a decreased level and activity of AR. By contrast, Skp2 knockdown increased the protein accumulation and activity of AR. Importantly, changes of AR contributed by Skp2 led to subsequent alterations of PSA level in PCa cells. AR ubiquitination was significantly increased upon Skp2 overexpression but greatly reduced upon Skp2 knockdown. AR mutant at K847R abrogated Skp2-mediated ubiquitination of AR. NVP-BEZ235, a dual PI3K/mTOR inhibitor, remarkably inhibited Skp2 level with a striking elevation of AR. The results indicate that Skp2 is an E3 ligase for proteasome-dependent AR degradation, and K847 on AR is the recognition site for Skp2-mediated ubiquitination. Our findings reveal an essential role of Skp2 in AR signaling.

Li B ，Lu W ，Yang Q ，Yu X ，Matusik RJ ，Chen Z ... -  《-》

SKP2 loss destabilizes EZH2 by promoting TRAF6-mediated ubiquitination to suppress prostate cancer.

Lu W ，Liu S ，Li B ，Xie Y ，Izban MG ，Ballard BR ，Sathyanarayana SA ，Adunyah SE ，Matusik RJ ，Chen Z ... -  《-》

Artemisinin disrupts androgen responsiveness of human prostate cancer cells by stimulating the 26S proteasome-mediated degradation of the androgen receptor protein.

Steely AM ，Willoughby JA Sr ，Sundar SN ，Aivaliotis VI ，Firestone GL ... -  《-》

Co-targeting SKP2 and KDM5B inhibits prostate cancer progression by abrogating AKT signaling with induction of senescence and apoptosis.

Prostate cancer (PCa) is the second-leading cause of cancer mortalities in the United States and is the most commonly diagnosed malignancy in men. While androgen deprivation therapy (ADT) is the first-line treatment option to initial responses, most PCa patients invariably develop castration-resistant PCa (CRPC). Therefore, novel and effective treatment strategies are needed. The goal of this study was to evaluate the anticancer effects of the combination of two small molecule inhibitors, SZL-P1-41 (SKP2 inhibitor) and PBIT (KDM5B inhibitor), on PCa suppression and to delineate the underlying molecular mechanisms. Human CRPC cell lines, C4-2B and PC3 cells, were treated with small molecular inhibitors alone or in combination, to assess effects on cell proliferation, migration, senescence, and apoptosis. SKP2 and KDM5B showed an inverse regulation at the translational level in PCa cells. Cells deficient in SKP2 showed an increase in KDM5B protein level, compared to that in cells expressing SKP2. By contrast, cells deficient in KDM5B showed an increase in SKP2 protein level, compared to that in cells with KDM5B intact. The stability of SKP2 protein was prolonged in KDM5B depleted cells as measured by cycloheximide chase assay. Cells deficient in KDM5B were more vulnerable to SKP2 inhibition, showing a twofold greater reduction in proliferation compared to cells with KDM5B intact (p < 0.05). More importantly, combined inhibition of KDM5B and SKP2 significantly decreased proliferation and migration of PCa cells as compared to untreated controls (p < 0.005). Mechanistically, combined inhibition of KDM5B and SKP2 in PCa cells abrogated AKT activation, resulting in an induction of both cellular senescence and apoptosis, which was measured via Western blot analysis and senescence-associated β-galactosidase (SA-β-Gal) staining. Combined inhibition of KDM5B and SKP2 was more effective at inhibiting proliferation and migration of CRPC cells, and this regimen would be an ideal therapeutic approach of controlling CRPC malignancy.

Brown LK ，Kanagasabai T ，Li G ，Celada SI ，Rumph JT ，Adunyah SE ，Stewart LV ，Chen Z ... -  《-》

Reciprocal feedback inhibition of the androgen receptor and PI3K as a novel therapy for castrate-sensitive and -resistant prostate cancer.

Qi W ，Morales C ，Cooke LS ，Johnson B ，Somer B ，Mahadevan D ... -  《Oncotarget》