Comparative Evaluation of Expression Patterns and Cellular Functions for the Three ZBTB Methyl-CpG Binding Proteins in Prostate Cancer

To date, prostate cancer (PCa) remains the most frequently diagnosed cancer in men. While some genetic mutations have been correlated with prostate tumorigenesis, many PCa presentations do not harbor a clear genetic mutation driver. In many cancers, including PCa, aberrant alterations in DNA methylation patterns has been correlated with cancer promotion and progression. The ZBTB methyl-CpG binding proteins (MBPs), consisting of ZBTB33 (Kaiso), ZBTB4 and ZBTB38, constitute a family of transcription factors that selectively recognize mCpG-containing sites. Upon DNA recognition, these MBPs recruit enzyme complexes that act to remodel chromatin and alter transcriptional outcomes. Given the role of these proteins in eliciting epigenetic-based transcription, we sought to comparably analyze protein levels and cellular distribution patterns for all three ZBTB MBPs within 123 cases of prostate adenocarcinomas exhibiting variable Gleason scores. It was generally observed that relative to benign, nuclear and/or cytoplasmic levels of all three ZBTB MBPs increased in prostate tumors, though the expression and predominant localization trends varied between family members and Gleason score. These tumor observations were generally recapitulated in multiple PCa cell line models, prompting comparative analysis of phenotypic and transcriptome alterations after systematic depletion of each ZBTB MBP. While functional overlap between family members was evident, each ZBTB MBP was also found to modulate distinct disease relevant transcription, including at gene targets known to be hyper-methylated in PCa tumors. Collectively, these findings represent the first comparative analysis of all three ZBTB MBP family members within the same disease context and suggest these proteins may be epigenetic-drivers of aberrant transcription in PCa. Determination of cellular and transcriptional consequences for ZBTB33, ZBTB4 or ZBTB38 depletion in PC3 cells. Three replicates of PC3 cells were transfected with either ZBTB33, ZBTB38, or ZBTB4 specific (si1 or si2) or control (Scr) siRNAs.