Abstract B028: Comparative assessment of cellular functions for the ZBTB methyl-CpG binding proteins in prostate cancer

It is becoming increasingly evident that DNA methylation patterns are misappropriated in a number of cancers. This leads to downstream alterations in transcription that afford a survival advantage for the disease state cells. In many cases, DNA methylation directs gene expression through the recruitment of methyl-CpG binding proteins (MBPs). These specialized factors read the methylated DNA signal and translate this into recruitment of chromatin remodeling complexes. The ZBTB family of MBPs, consisting of ZBTB33, ZBTB4, and ZBTB38, are unique among MBPs in that they utilize a single protein domain to specifically target both methylated and sequence-specific nonmethylated DNA sites. This bimodality in DNA recognition affords these proteins the ability to effect either transcriptional repression or activation depending on the cellular context. Further, there is mounting evidence that overexpression of ZBTB MBPs and their subsequent transcriptional activities are directly associated with cancer, though the mechanism by which each protein functions to maintain and/or progress the disease state remains to be elucidated. Of particular note, ZBTB33 overexpression has been correlated with tumorigenicity in prostate cancer (PCa). In these studies we sought to begin more thoroughly characterizing the role of ZBTB33 in PCa, and simultaneously evaluating whether ZBTB38 and ZBTB4 may also participate in this disease. Utilizing both cell line models and patient PCa tumors, we demonstrate that protein levels for all three ZBTB MBPs increase in the cancerous state relative to normal cells/tissues. Notably, the expression levels of ZBTB4 appear to peak at earlier stage disease and decrease at later. To begin delineating the biologic pathways mediated by each ZBTB MBP, we evaluated global transcriptome (RNA-seq) and phenotypic alterations after systematic ZBTB MBP depletion in two phenotypically distinct PCa cell line models. Specifically, we evaluated the impact of each ZBTB MBP on cell proliferation, apoptosis, and migration. In short, we determined that cellular phenotypic response to depletion of the three ZBTB MBPs appears highly variable between proteins as well as cell line model. Further, comparative RNA-seq after depletion of each ZBTB MBP demonstrates that consistent with the phenotypic analyses, each ZBTB MBP appears to mediate protein-specific transcriptional responses. These findings suggest that these proteins may function in parallel within PCa. Combined, these studies represent the first comprehensive analysis of all three ZBTB MBPs in the same disease context and emphasize the potential for these proteins as novel therapeutic targets. Citation Format: Amir Pozner, Aneesa T. Al-Soodani, Sheryl Tripp, Justin Caron, Daniel J. Albertson, Bethany A. Buck-Koehntop. Comparative assessment of cellular functions for the ZBTB methyl-CpG binding proteins in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B028.