Abstract 5713: Alternative splicing of the chromatin modifier gene BAZ1A in colorectal cancer

Abstract

Abstract Bromodomain Adjacent to Zinc finger Domain 1A (BAZ1A) is a non-catalytic subunit of the ATP-dependent chromatin assembly factor that regulates key cellular processes such as DNA replication, chromatin assembly, DNA repair, and transcriptional gene regulation (1). Defective DNA repair is a hallmark of cancer etiology, and BAZ1A is one of the deregulated proteins in colorectal cancer. The BAZ1A transcript exhibits full-length and truncated forms, generated via alternative splicing of exon-13. We observed that the histone deacetylase inhibitor sulforaphane (SFN) modulated alternative splicing of BAZ1A in human colon cancer cells by increasing the relative expression of the short vs. the long transcript. Cell Cycle and Apoptosis Regulator 2 (CCAR2) and Zinc finger protein 326 (ZIRD) are components of the DBIRD complex that integrates alternative splicing and the rate of transcript elongation (2). Knockdown of DBIRD members, including ZIRD and splicing factor hnRNPA1, downregulated expression of BAZ1A long form, whereas the BAZ1A short form was unaltered. Previous studies in SFN-treated colon cancer cells revealed that the BAZ1A bromodomain recognized a novel K97 acetylation site in CCAR2 (3). Co-immunoprecipitation analyses revealed that CCAR2 and BAZ1A interacted with each other in the presence and absence of SFN. On investigating the involvement of CCAR2 in BAZ1A alternative splicing, SFN treatment increased the expression of both BAZ1A long and short forms in CCAR2-/- HCT116 colon cancer cells. Although the total expression of BAZ1A was influenced by CCAR2 loss, alternative splicing of BAZ1A was independent of DBIRD complex-mediated regulation. Pursuing the role of p53 and p21 in BAZ1A alternative splicing, SFN treatment increased the expression of BAZ1A short form in p21-/- HCT116 cells, whereas this was impaired in p53-/- HCT116 cells. Overall, this investigation provided mechanistic insights into the regulation of alternative splicing in SFN-treated colon cancer cells, and BAZ1A functionalities that might be targeted via next-generation combinatorial epigenetic agents (4). Supported in part by NCI grant CA122959, by the John S. Dunn Foundation, and by a Chancellor’s Research Initiative.