Abnormal Wnt/?-catenin signaling is associated with various types of human cancers, most notably colorectal cancers (CRCs) due to APC and CTNNB1 (?-catenin) mutations. CRCs are the third most common cancer worldwide and the fourth most common cause of death. Wnt/?-catenin signaling exhibits its oncogenic activities by inducing the expression of Wnt target genes such as CCND1 (Cyclin D1) and MYC (c-Myc) through ?-catenin/T cell factor (Tcf)-mediated transcription. Although APC and CTNNB1 mutations play a critical role in human CRC initiation and development, emerging evidence suggests that epigenetic modifications act synergistically in human CRC initiation and development. A small subset of cancer stem cells (CSCs) or cancer initiating cells with the ability to self-renew and maintain the tumor has been isolated from human CRCs. We and others have found that ?-catenin/Tcf-mediated transcription is hyperactivated in human colorectal CSCs compared to non-CSC tumor cells. In this application, we identified that lysine-specific demethylase 4B (KDM4B) that erases H3K9me3 marks was highly expressed in human CRCs. The knockdown or pharmacological inhibition of KDM4B in human CRC cells significantly inhibited the expression of Wnt target genes. To explore the functional roles of KDM4B in vivo, we generated Kdm4bflox/flox (Kdm4bf/f) mice that carry conditional Kdm4b alleles. Although the deletion of Kdm4b in mice causes intestinal abnormalities and reduced crypt stem cells, unlike the deletion of ?-catenin, we found that mice can tolerate KDM4B deficiency, indicating that targeting KDM4B might provide a safe therapeutic window for the treatment of human CRCs. Consistently, we found that the intestinal deletion of Kdm4b completely inhibited intestinal tumorigenesis in ApcMin/+ mice which develop multiple adenomas in the small intestine due to increased ?-catenin/Tcf-mediated transcription. Additionally, we found that KDM4B interacts with the intestinal stem cell transcription factor ASCL2 which serve as a positive feedback to enhance ?-catenin/Tcf-mediated transcription. Based on these exciting discoveries, we hypothesize that KDM4B might epigenetically control Wnt/?-catenin-mediated oncogenesis and is required for the tumorigenic potentials of human colorectal CSCs. Using molecular, cellular, genetic and epigenetic approaches, we will determine: 1) Whether the knockout or pharmacological inhibition of KDM4B inhibits CRC tumorigenesis in vivo; 2) Whether KDM4B epigenetically controls tumorigenic potentials and self-renewal of CSCs in human CRCs; 3) How KDM4B epigenetically controls Wnt/?-catenin-mediated transcription and tumorigenesis by erasing H3K9me3. Since histone demethylases are enzymes which can be readily targeted by small molecules inhibitors, novel findings from our studies may lead to develop novel strategies for the treatment of human CRCs and other cancers.
Our application is to examine how epigenetic factors control colorectal cancer (CRC) development and cancer stem cell functions and to determine whether target epigenetic factors inhibits CRC growth. The discoveries from this study will have important implications in developing novel therapeutic strategies for treating human CRCs.
