Abstract 1712: Identifying a novel alternative promoter usage in HDAC9: Implications for LUAD prognosis and therapy
Authors: Bolatkan Amina , Asada Ken , Kaneko Syuzo , Komatsu Masaaki , Hamamoto Ryuji 
Published: March 2024

Abstract
Promoters are key elements in gene regulation. It has been estimated that more than half of protein-coding genes in the human genome possess multiple promoters. Aberrant expression and dysregulated activity of alternative promoters have been correlated with numerous diseases, especially cancer. In this study, we utilized RNA-seq data from 608 lung adenocarcinoma (LUAD) patients and systematically analyzed promoter activities using the proActiv algorithm. Of the expressed genes in LUAD, approximately 57% have at least two distinct promoters. In addition, we identified 1852 tumor-specific alternative promoters that showed a significant shift (2-fold changes) in promoter activity without any notable changes in the expression of corresponding 1603 genes between tumor and adjacent non-tumor tissues. Functional enrichment analysis showed that these genes were associated with key cellular functions such as signaling pathways, cell cycle, and cell junctions. Unsupervised clustering of patients based on altered promoters revealed a significant prognostic value. Among them, we observed a major promoter switch in HDAC9, which mainly utilizes three promoters: prmt3280, prmt3283, and prmt3287 in our LUAD dataset. Notably, prmt3287 was exclusively active in tumor samples and functioned as the dominant promoter, while prmt3283 served as the main promoter in adjacent non-tumor samples. Intriguingly, even though the overall expression of HDAC9 mRNA lacked prognostic relevance both in our dataset and in the TCGA dataset, higher expression of the alternative promoter prmt3287 (using ≥50% activity level as a cutoff) was associated with adverse outcomes in LUAD patients. We further compared the DNA methylation level around the HDAC9 domain between paired tumor and non-tumor samples and found that positions with the most significant differences (p&lt;0.001) overlapped with the prmt3287 region. Moreover, DNA methylation levels around prmt3287 significantly decreased in prmt3287 high-activity patient groups. Next, we investigated the ChIP-seq levels over the HDAC9 region, and ChIPseeker successfully annotated the alternative promoters of HDAC9. In addition, the alternative promoter prmt3287 exhibited the highest active enhancer signals. Furthermore, we performed PCR to determine the expression of six distinct transcript isoforms from alternative promoters in four different LUAD cell lines, and we observed high expression of isoform 10, which is possibly generated by prmt3287 in all cell lines. The impact of prmt3287 on cell proliferation, cell cycle, and cell migration will be further addressed. Our results indicate that alternative promoter usage can capture insights that might be missed at the overall gene expression level, and alternative promoter usage in HDAC9 could be a novel biomarker and a promising therapy target.
Citation Format: Amina Bolatkan, Ken Asada, Syuzo Kaneko, Masaaki Komatsu, Ryuji Hamamoto. Identifying a novel alternative promoter usage in HDAC9: Implications for LUAD prognosis and therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1712.