Abstract 2419: Genome-wide profiling of PAK4 DNA-binding sites and transcriptome reveals its potential transcriptional control on DNA repair-related genes in ovarian cancer cells
Authors: Wong Ivy Tsz-Lo , Wong Oscar Gee-Wan , Qin Yiming , Wang Junwen , Cheung Annie Nga-Yin 
Published: July 2017

Oncogenic role of p21-activated protein 4 (PAK4) in relation to cell growth and migration through various signalling cascades has been well studied in multiple cancer types. Such role might be contributed largely by cytoplasmic PAK4 as most of the known PAK4 signalling events occur in the cytoplasm. However, recent studies have demonstrated that PAK4 is capable of shuttling between nucleus and cytoplasm. The precise function of nuclear PAK4 (nPAK4) remains substantially unexplored. We have previously shown that PAK4 can act as a transcription factor. Herein, we aim to identify nPAK4-regulated genes by delineating the PAK4-binding landscape in ovarian cancer genome and mapping the PAK4 transcriptome in ovarian cancer cells.

PAK4-enriched genomic regions were identified by chromatin immunoprecipitation with a PAK4 antibody followed by next-generation sequencing (ChIP-seq) in OVCAR3 cells. PAK4 transcriptome data was generated using RNA extracted from SKOV3 cells stably expressing PAK4 in the Affymetrix GeneChIP® Human Transcriptome Array 2.0 system. Gene lists generated from both ChIP-seq and microarray dataset were subjected to pathway enrichment analysis by Partek® PathwayTM. Among the 20 most significantly enriched pathways from microarray studies, several pathways in which PAK4 has no known reported function by far have been identified. Notably, DNA repair pathways that are known to influence drug chemosensitivity in ovarian cancer, such as the nucleotide excision repair (p=0.008), homologous recombination (p=0.012), mismatch repair (p=0.018) and DNA replication (p=0.018) pathways were significantly enriched. In concordance with the findings, the nucleotide excision repair pathway was also significantly enriched (p&lt;0.006) in the gene list derived from promoter-restricted PAK4 binding sites in the ovarian cancer genome. Among the many candidates that were deregulated by PAK4, cyclin-dependent kinase 7 (CDK7), a core component in the CAK subcomplex crucial to nucleotide excision repair pathway, was further validated. The transcription start site (TSS) of cyclin-dependent kinase 7 (CDK7) was bound by PAK4. CDK7 mRNA expression was upregulated upon PAK4 overexpression. Quantitative-PCR showed downregulated CDK7 mRNA expression upon siRNA-mediated knockdown of PAK4 in OVCAR3 and TUOS3. This study points to the possible role of PAK4 in regulating gene transcription as PAK4 is mapped to several core promoter/TSS regions in the ovarian cancer genome. Our findings also shed light into the potential role of PAK4 in regulating drug chemosensitivity via its transcriptional control on genes implicated in DNA repair pathways. We postulate CDK7 as a direct transcriptional target of PAK4 and thereby contributes to chemoresistance in ovarian cancer cells.

Citation Format: Ivy Tsz-Lo Wong, Oscar Gee-Wan Wong, Yiming Qin, Junwen Wang, Annie Nga-Yin Cheung. Genome-wide profiling of PAK4 DNA-binding sites and transcriptome reveals its potential transcriptional control on DNA repair-related genes in ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2419. doi:10.1158/1538-7445.AM2017-2419