Bladder cancer is a highly prevalent human disease in which retinoblastoma (Rb) pathway inactivation and epigenetic alterations are common events. However, the connection between these two processes is still poorly understood. Here, we show that the in vivo inactivation of all Rb family genes in the mouse urothelium is sufficient to initiate bladder cancer development. The characterization of the mouse tumors revealed multiple molecular features of human bladder cancer, including the activation of E2F transcription factor and subsequent Ezh2 expression and the activation of several signaling pathways previously identified as highly relevant in urothelial tumors. These mice represent a genetically defined model for human high-grade superficial bladder cancer. Whole transcriptional characterizations of mouse and human bladder tumors revealed a significant overlap and confirmed the predominant role for Ezh2 in the downregulation of gene expression programs. Importantly, the increased tumor recurrence and progression in human patients with superficial bladder cancer is associated with increased E2F and Ezh2 expression and Ezh2-mediated gene expression repression. Collectively, our studies provide a genetically defined model for human high-grade superficial bladder cancer and demonstrate the existence of an Rb–E2F–Ezh2 axis in bladder whose disruption can promote tumor development. Cancer Res; 74(22); 1–13. ©2014 AACR.

Bladder cancer (BC) is a highly prevalent human disease in which retinoblastoma (Rb) pathway inactivation and epigenetic alterations are common events. However, the connection between these two processes is still poorly understood. Here we show that the in vivo inactivation of all Retinoblastoma (Rb) family genes in the mouse urothelium is sufficient to initiate BC development. The characterization of the mouse tumors revealed multiple molecular features of human BC, including the activation of E2F transcription factor and subsequent Ezh2 expression, and the activation of several signaling pathways previously identified as highly relevant in urothelial tumors. These mice represent a genetically defined model for human high-grade superficial BC. Whole transcriptional characterizations of mouse and human bladder tumors revealed a significant overlap and confirm the predominant role for Ezh2 in the downregulation of gene expression programs. Importantly, the increased tumor recurrence and progression in human superficial BC patients is associated with increased E2F and Ezh2 expression and Ezh2-mediated gene expression repression. Collectively, our studies provide a genetically defined model for human high-grade superficial BC and demonstrate the existence of an Rb-E2F-Ezh2 axis in bladder whose disruption can promote tumor development.

Obesity is a pandemic and major risk factor for cancers. The reduction of obesity would have been an effective strategy for cancer prevention, but the reality is that worldwide obesity has kept increasing for decades, remaining a major avoidable cancer risk secondary only to smoke. The present studies suggest that vitamin D may be an effective agent to reduce obesity-associated cancer risks in women. Molecular analyses showed that leptin increased human telomerase reverse transcriptase (hTERT) mRNA expression and cell growth through estrogen receptor-α (ERα) activation in ovarian cancer cells, which was suppressed by 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3]. The suppression was compromised when miR-498 induction by the hormone was depleted with microRNA (miRNA) sponges. In mice, high-fat diet (HFD) stimulation of ovarian tumor growth was remarkably suppressed by 1,25(OH)2D3 analogue EB1089, which was also compromised by miR-498 sponges. EB1089 did not alter HFD-induced increase in serum leptin levels but increased miR-498 and decreased the diet-induced hTERT expression in tumors. Quantitative RT-PCR analyses revealed an inverse correlation between hTERT mRNA and miR-498 in response to 1,25(OH)2D3 in estrogen-sensitive ovarian, endometrial, and breast cancers. The studies suggest that miR-498-mediated hTERT downregulation is a key event mediating the anti-leptin activity of 1,25(OH)2D3 in estrogen-sensitive tumors in women. Cancer Res; 74(21); 1–11. ©2014 AACR.

Obesity is a pandemic and major risk factor for cancers. The reduction of obesity would have been an effective strategy for cancer prevention, but the reality is that worldwide obesity has kept increasing for decades, remaining a major avoidable cancer risk secondary only to smoke. The present studies suggest that vitamin D may be an effective agent to reduce obesity-associated cancer risks in women. Molecular analyses showed that leptin increased human telomerase reverse transcriptase (hTERT) mRNA expression and cell growth through estrogen receptor alpha (ERα) activation in ovarian cancer (OCa) cells, which was suppressed by 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3]. The suppression was compromised when miR-498 induction by the hormone was depleted with miRNA sponges. In mice, high-fat diet (HFD) stimulation of ovarian tumor growth was remarkably suppressed by 1,25(OH)2D3 analogue EB1089, which was also compromised by miR-498 sponges. EB1089 did not alter HFD-induced increase in serum leptin levels but increased miR-498 and decreased the diet-induced hTERT expression in tumors. Quantitative RT-PCR (qRT-PCR) analyses revealed an inverse correlation between hTERT mRNA and miR-498 in response to 1,25(OH)2D3 in estrogen-sensitive ovarian, endometrial and breast cancers. The studies suggest that miR-498-mediated hTERT down regulation is a key event mediating the anti-leptin activity of 1,25(OH)2D3 in estrogen-sensitive tumors in women.

Prostate cancer is thought to be driven by oxidative stress, lipid metabolism, androgen receptor (AR) signaling, and activation of the PI3K–AKT–mTOR pathway, but it is uncertain how they may become coordinated during progression to castration-resistant disease that remains incurable. The mitotic kinase polo-like kinase 1 (Plk1) is elevated in prostate cancer, where its expression is linked to tumor grade. Notably, Plk1 signaling and lipid metabolism were identified recently as two of the top five most upregulated pathways in a mouse xenograft model of human prostate cancer. Herein, we show that oxidative stress activates both the PI3K–AKT–mTOR pathway and AR signaling in a Plk1-dependent manner in prostate cells. Inhibition of the PI3K–AKT–mTOR pathway prevented oxidative stress-induced activation of AR signaling. Plk1 modulation also affected cholesteryl ester accumulation in prostate cancer via the SREBP pathway. Finally, Plk1 inhibition enhanced cellular responses to androgen signaling inhibitors (ASI) and overcame ASI resistance in both cultured prostate cancer cells and patient-derived tumor xenografts. Given that activation of AR signaling and the PI3K–AKT–mTOR pathway is sufficient to elevate SREBP-dependent expression of key lipid biosynthesis enzymes in castration-resistant prostate cancer (CRPC), our findings argued that Plk1 activation was responsible for coordinating and driving these processes to promote and sustain the development of this advanced stage of disease. Overall, our results offer a strong mechanistic rationale to evaluate Plk1 inhibitors in combination drug trials to enhance the efficacy of ASIs in CRPC. Cancer Res; 74(22); 1–13. ©2014 AACR.