E2F6 functions as a competing endogenous RNA, and transcriptional repressor, to promote ovarian cancer stemness

Ovarian cancer is the most lethal cancer of the female reproductive system. In that regard, several epidemiological studies suggest that long‐term exposure to estrogen could increase ovarian cancer risk, although its precise role remains controversial. To decipher a mechanism for this, we previously generated a mathematical model of how estrogen‐mediated upregulation of the transcription factor, E2F6, upregulates the ovarian cancer stem/initiating cell marker, c‐Kit, by epigenetic silencing the tumor suppressor miR‐193a, and a competing endogenous (ceRNA) mechanism. In this study, we tested that previous mathematical model, showing that estrogen treatment of immortalized ovarian surface epithelial cells upregulated both E2F6 and c‐KIT, but downregulated miR‐193a. Luciferase assays further confirmed that microRNA‐193a targets both E2F6 and c‐Kit. Interestingly, ChIP‐PCR and bisulphite pyrosequencing showed that E2F6 also epigenetically suppresses miR‐193a, through recruitment of EZH2, and by a complex ceRNA mechanism in ovarian cancer cell lines. Importantly, cell line and animal experiments both confirmed that E2F6 promotes ovarian cancer stemness, whereas E2F6 or EZH2 depletion derepressed miR‐193a, which opposes cancer stemness, by alleviating DNA methylation and repressive chromatin. Finally, 118 ovarian cancer patients with miR‐193a promoter hypermethylation had poorer survival than those without hypermethylation. These results suggest that an estrogen‐mediated E2F6 ceRNA network epigenetically and competitively inhibits microRNA‐193a activity, promoting ovarian cancer stemness and tumorigenesis.

Abstract 74: E2F6-mediated ceRNA and epigenetic silencing of miR193a lead to cancer stemness and anticancer immunity in ovarian cancer

Ovarian cancer is one of the most lethal cancers in the female reproductive system. Previous study suggested that long term treatment of estrogen such as hormonal replacement therapy (HRT) may increase the risk of ovarian cancer, however the role of estrogen in ovarian carcinogenesis is still controversial. To decipher this complicated process, we generated a mathematical model and found that estrogen-mediated up-regulation of E2F6 could upregulate the ovarian cancer stem/initiating marker, c-kit by two means one through epigenetic silencing of their co-targeted miR193a by binding of E2F6 which subsequently recruit EZH2 to miR-193a promoter; and second, by competing endogenous (ceRNA) mechanism. To confirm this model, treatment of E2 or environmental hormone, BPA resulted in upregulation of both E2F6 and c-kit but down-regulation of miR-193a in immortalized ovarian surface epithelial cells. Further bisulfite pyrosequencing, ChIP-qPCR and epigenetic treatment found that miR193a was epigenetically silenced by DNA methylation and H3K27me3 in CP70 but not HeyC2 ovarian cancer cells. Overexpression of miR193a inhibited tumor growth in vitro and in vivo. Depletion of EZH2 or E2F6 in CP70 restored miR-193a expression and decreased the number of “ovo” spheroid by reversing the repressive chromatin status of miR-193a promoter. To further explore the biological significance of this E2F6 ceRNA network, integrative RNA-Seq and computational analysis found that PBX1, a miR-193a target and transcriptional activator of the immunosuppressive cytokine IL-10, was down-regulated in E2F6 and EZH2 knockdown CP70 cells. Overexpression of E2F6 3'UTR containing miR-193a MRE but not MRE mutant increased the expression of PBX1 and IL10 in ovarian cancer cells. Importantly, co-culture of conditional media from E2F6 3'UTR overexpressing CP70 cells inhibited the differentiation of THP-1 monocytes into dendritic cell and the T-cell activating function of this THP-1 derived DC. This phenomenon can be rescued by incubation of anti-IL-10 antibody or pretreatment of CP70 cells with EZH2 inhibitor. Finally, clinical studies demonstrated that patients with higher promoter methylation of miR193a were associated with poor survival. Serum IL10 level was found to be higher in high staged ovarian cancer patients and patients with higher E2F6 mRNA level. Additional analysis from TCGA ovarian cancer expression microarray dataset demonstrated that ovarian cancer patients with low expression of EZH2, showed a positive correlation between E2F6, c-KIT and PBX1 resembling the ceRNA phenomenon between these mRNAs. Taken together, our results showed that estrogen-mediated E2F6 ceRNA network can regulate cancer stemness and anti-tumor immunity of DC through epigenetic silencing of miR-193a. Anti-estrogen therapy together with the EZH2 inhibitor may be a novel strategy against this deadly cancer.

Citation Format: Frank Hsueh-Che Cheng, Hon-Yi Lin, Yin-Chen Chen, Tzy-Wei Hwang, Rui-Lan Huang, Chia-Bin Chang, Ru-Inn Lin, Ching-Wen Lin, Gary C.W. Chen, Jora M. J. Lin, Yu-Ming Chuang, Jian-Liang Chou, Chin Li, Alfred S.L. Cheng, Hung-Cheng Lai, Shu-Fen Wu, Je-Chiang Tsai, Michael W.Y. Chan. E2F6-mediated ceRNA and epigenetic silencing of miR193a lead to cancer stemness and anticancer immunity in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 74.

Abstract 950: Bistable switching of c-KIT by estrogen-mediated ceRNA and epigenetic silencing of miR-193a predicts survival in ovarian cancer

Ovarian cancer is one of the most lethal cancers in the female reproductive system. Our previous study has shown that ovarian cancer may be initiated by ovarian cancer initiating cells (OCIC) characterized by the surface antigen CD44 and c-KIT (CD117). Previous study also suggested that long term treatment of estrogen such as hormonal replacement therapy (HRT) may increase the risk of ovarian cancer, however the role of estrogen in ovarian carcinogenesis is still controversial. To unravel this complexity, we propose a mathematical model to explore how the ER signaling pathway contribute to c-KIT expression during ovarian carcinogenesis: one through a ceRNA competition of an ER target,E2F6 and c-KIT for their targeted miRNA, miR-193a; second by binding of E2F6 protein, in association with the polycomb complex, to the promoter of miR-193a to downregulate miR-193a transcription by epigenetic modifications. Our model found that epigenetic silencing of miR-193a generates a bistable switching of c-KIT during ovarian carcinogenesis based on the level of EZH2. To confirm our results, we performed ectopic expression of miR-193a and 3’UTR luciferase in ovarian cancer cell lines and confirmed that E2F6 and c-KIT are the targets of miR-193a. Importantly, treatment of E2 or bisphenol A (BPA) resulted in the up-regulation of E2F6 and c-kit mRNA in IOSE cells in which no or low methylation at the promoter CpG island of miR-193a was found. On the contrary, promoter hypermethylation of miR193a could be observed in miR-193a-underexpressed CP70 ovarian cancer cells but not in HeyC2 cells which showed similar expression level of miR-193a as in IOSE cells. Treatment of demethylating agent (5azaDC) or EZH2 inhibitor (GSK343) resulted in a reexpression of miR-193a in CP70 ovarian cancer cells. Overexpression of miR-193a inhibited tumor growth in vitro and in an animal model. Further ChIP-PCR assay also found that open chromatin mark H3K4me3 was enriched in the promoter region of miR-193a in HeyC2 but not in CP70 cells. On the contrary, repressive chromatin marks H3K9me3 and H3K27me3 were only enriched in CP70 cells. Clinically, ovarian cancer patients (n = 109) with higher promoter methylation of miR-193a were associated with poor survival (p>0.05). Additional analysis of the TCGA ovarian cancer dataset demonstrated that ovarian cancer patients with low expression of EZH2, a polycomb-group protein, showed positive correlation (p<0.05) between E2F6 and c-KIT which resembles the ceRNA phenomenon between these two mRNAs. Importantly, ovarian cancer patients with low expression of EZH2 tended to have lower expression of c-KIT. In conclusion, our mathematical model and experimental data suggests that miR-193a can be epigenetically regulated by both ceRNA and promoter methylation. Simultaneous EZH2 inhibition and anti-estrogen therapy can constitute an effective combined therapeutic strategy against ovarian cancer.

Citation Format: Frank Hsueh-Che Cheng, Baltazar D. Aguda, Hon-Yi Lin, Je-Chiang Tsai, Marek Kochanczyk, Ru-Inn Lin, Jora M. J. Lin, Gary C. W. Chen, Cheng-Chang Chang, Hung-Cheng Lai, Kenneth P. Nephew, Tzy-Wei Hwang, Michael W. Y. Chan. Bistable switching of c-KIT by estrogen-mediated ceRNA and epigenetic silencing of miR-193a predicts survival in ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 950.

A mathematical model of bimodal epigenetic control of miR-193a in ovarian cancer stem cells

Accumulating data indicate that cancer stem cells contribute to tumor chemoresistance and their persistence alters clinical outcome. Our previous study has shown that ovarian cancer may be initiated by ovarian cancer initiating cells (OCIC) characterized by surface antigen CD44 and c-KIT (CD117). It has been experimentally demonstrated that a microRNA, namely miR-193a, targets c-KIT mRNA for degradation and could play a crucial role in ovarian cancer development. How miR-193a is regulated is poorly understood and the emerging picture is complex. To unravel this complexity, we propose a mathematical model to explore how estrogen-mediated up-regulation of another target of miR-193a, namely E2F6, can attenuate the function of miR-193a in two ways, one through a competition of E2F6 and c-KIT transcripts for miR-193a, and second by binding of E2F6 protein, in association with a polycomb complex, to the promoter of miR-193a to down-regulate its transcription. Our model predicts that this bimodal control increases the expression of c-KIT and that the second mode of epigenetic regulation is required to generate a switching behavior in c-KIT and E2F6 expressions. Additional analysis of the TCGA ovarian cancer dataset demonstrates that ovarian cancer patients with low expression of EZH2, a polycomb-group family protein, show positive correlation between E2F6 and c-KIT. We conjecture that a simultaneous EZH2 inhibition and anti-estrogen therapy can constitute an effective combined therapeutic strategy against ovarian cancer.

Host extinction dynamics in a simple parasite-host interaction model

This short article carefully formulate a simple SI model for a parasite-host interaction through the basic birth and death processes analysis. This model reveals and corrects an error in similar models studied recently by various authors. Complete mathematical investigation of this simple model shows that the host extinction dynamics can happen and the outcomes may depend on the initial conditions. We also present biological implications of our findings.

A ratio-dependent food chain model and its applications to biological control

While biological controls have been successfully and frequently implemented by nature and human, plausible mathematical models are yet to be found to explain the often observed deterministic extinctions of both pest and control agent in such processes. In this paper we study a three trophic level food chain model with ratio-dependent Michaelis-Menten type functional responses. We shall show that this model is rich in boundary dynamics and is capable of generating such extinction dynamics. Two trophic level Michaelis-Menten type ratio-dependent predator-prey system was globally and systematically analyzed in details recently. A distinct and realistic feature of ratio-dependence is its capability of producing the extinction of prey species, and hence the collapse of the system. Another distinctive feature of this model is that its dynamical outcomes may depend on initial populations levels. Theses features, if preserved in a three trophic food chain model, make it appealing for modelling certain biological control processes (where prey is a plant species, middle predator as a pest, and top predator as a biological control agent) where the simultaneous extinctions of pest and control agent is the hallmark of their successes and are usually dependent on the amount of control agent. Our results indicate that this extinction dynamics and sensitivity to initial population levels are not only preserved, but also enriched in the three trophic level food chain model. Specifically, we provide partial answers to questions such as: under what scenarios a potential biological control may be successful, and when it may fail. We also study the questions such as what conditions ensure the coexistence of all the three species in the forms of a stable steady state and limit cycle, respectively. A multiple attractor scenario is found.

Deterministic extinction effect of parasites on host populations

Experimental studies have shown that parasites can reduce host density and even drive host population to extinction. Conventional mathematical models for parasite-host interactions, while can address the host density reduction scenario, fail to explain such deterministic extinction phenomena. In order to understand the parasite induced host extinction, Ebert et al. (2000) formulated a plausible but ad hoc epidemiological microparasite model and its stochastic variation. The deterministic model, resembles a simple SI type model, predicts the existence of a globally attractive positive steady state. Their simulation of the stochastic model indicates that extinction of host is a likely outcome in some parameter regions. A careful examination of their ad hoc model suggests an alternative and plausible model assumption. With this modification, we show that the revised parasite-host model can exhibit the observed parasite induced host extinction. This finding strengthens and complements that of Ebert et al. (2000), since all continuous models are likely break down when all population densities are small. This extinction dynamics resembles that of ratio-dependent predator-prey models. We report here a complete global study of the revised parasite-host model. Biological implications and limitations of our findings are also presented.

Rich dynamics of a ratio-dependent one-prey two-predators model

The objective of this paper is to systematically study the qualitative properties of a ratio-dependent one-prey two-predator model. We show that the dynamics outcome of the interactions are very sensitive to parameter values and initial data. Specifically, we show the interactions can lead to all the following possible outcomes: 1). competitive exclusion; 2). total extinction, i.e., collapse of the whole system; 3). coexistence in the form of positive steady state; 4). coexistence in the form of oscillatory solutions; and 5). introducing a friendly and better competitor can save a otherwise doomed prey species. These results reveal far richer dynamics compared to similar prey dependent models. Biological implications of these results are discussed.

Global analysis of the Michaelis-Menten-type ratio-dependent predator-prey system

The recent broad interest on ratio-dependent based predator functional response calls for detailed qualitative study on ratio-dependent predator-prey differential systems. A first such attempt is documented in the recent work of Kuang and Beretta(1998), where Michaelis-Menten-type ratio-dependent model is studied systematically. Their paper, while contains many new and significant results, is far from complete in answering the many subtle mathematical questions on the global qualitative behavior of solutions of the model. Indeed, many of such important open questions are mentioned in the discussion section of their paper. Through a simple change of variable, we transform the Michaelis-Menten-type ratio-dependent model to a better studied Gause-type predator-prey system. As a result, we can obtain a complete classification of the asymptotic behavior of the solutions of the Michaelis-Menten-type ratio-dependent model. In some cases we can determine how the outcomes depend on the initial conditions. In particular, open questions on the global stability of all equilibria in various cases and the uniqueness of limit cycles are resolved. Biological implications of our results are also presented.

Acoustic emission monitoring of high speed grinding of silicon nitride

Acoustic emission (AE) monitoring of a machining process offers real-time sensory input which could provide tool condition and part quality information that is critical to effective process control. However, the choice of sensor, its placement, and how to process the data and extract useful information are challenging application-specific questions which researchers must consider. Here we report an effort to resolve these questions for the case of high speed grinding of silicon nitride using an electroplated single-layered diamond wheel. A grinding experiment was conducted at a wheel speed of 149 m s-1 and continued until the end of the useful wheel life. AE signal data were then collected for each complete pass at given grinding times throughout the useful wheel life. We found that the amplitude of the AE signal monotonically increases with wheel wear, as do grinding forces and energy. Furthermore, the signal power contained in the AE signal proportionally increases with the associated grinding power, which suggests that the AE signal could provide quantitative information of wheel wear in high-speed grinding, and could also be used to determine when the grinding wheel needs replacement.