Delineating the Role of KAP1 in WNT-induced Colorectal Cancer

点击翻译按钮获取中文摘要

PROJECT SUMMARY Cell signaling - transcriptional programs play diverse roles in normal development including the regulation of metabolism, cell survival/death, and differentiation, all of which can malfunction in tumorigenesis. The WNT program maintains cell stemness and is highly proliferative, properties that cancer cells hijack to initiate and sustain tumorigenesis. A large body of work has defined that the WNT program is important for both CRC initiation and progression. However, despite previous molecular characterization and identification of small molecules that target the WNT program at multiple levels, a therapeutic arm that successfully inactivates WNT has yet to be employed. Our studies have defined that the transcriptional coregulator KAP1/TRIM28 is required for expression of WNT target genes upon oncogenic WNT activation, suggesting that KAP1 is an alternative drug target in WNT-induced CRC. As such, targeting KAP1 in CRC will require comprehensive characterization of druggable pockets, that if perturbed, would prevent KAP1-dependent oncogenic WNT activation and downstream hallmarks of cancer. Our published studies have identified a mechanism whereby KAP1 uses a previously uncharacterized chromatin reader cassette to directly bind hypoacetylated Histone 4 tails surrounding promoters of non-WNT genes (to facilitate their activation). Our unpublished studies have provided evidence of KAP1 interaction with the pathway- and sequence-specific factor β-Catenin. However, it remains unknown if the chromatin- and β-Catenin–binding activities are critical for KAP1 recruitment to, and for activation of, WNT target genes to support WNT-dependent hallmarks of cancer. Given these findings and critical gaps in knowledge, the central hypothesis of this proposal is that KAP1 uses its chromatin- and β-Catenin–binding functions to activate the oncogenic WNT program to promote CRC transformation and proliferation. As such, the major goal of this research proposal is to explore if KAP1 utilizes these functions to activate WNT target genes, and whether their perturbation would block WNT target gene activation and WNT-induced CRC phenotypes (CRC transformation and cell proliferation). To accomplish this goal, we will leverage the power of genomics (integrated RNA-seq/ChIP-seq approach) and phenotypic assays in established models of CRC tumorigenesis (normal and oncogenic colon epithelial cells). Specifically, we will explore if KAP1 binds WNT target loci upon oncogenic WNT activation in normal colon epithelial cells and whether KAP1 chromatin- and β-Catenin–binding capabilities are required to activate WNT target genes (Aim 1) and to sustain hallmarks of cancer (Aim 2). The basic science research proposed in this “self-contained proposal” will not only reveal fundamental principles of how chromatin readers operate in the context of cancer but also pave the way to identify KAP1 targeting approaches, which is in-line with NCI’s mission to identify novel therapeutic targets to move the discoveries from the bench to the clinics.