LAUSR

Background: Epigenetic alterations can impact gene expression and have been implicated in tumorigenesis. One major process is the post-translational modification (PTM) of histone proteins governed by histone-modifying enzyme (HME) activity. There is growing evidence that the dysregulation of HMEs plays an essential role in cancer initiation and progression. In this study, we hypothesized that alterations in histone PTMs and their associated enzymes drive the development of castration-resistant prostate cancer (CRPC) from hormone-sensitive prostate cancer (HSPC). To address this, we performed an unbiased screen of histone PTMs in a series of prostate cancer (PC) PDXs before and after the transition to CRPC. Methods: Histone PTM levels were analyzed in 10 paired HSPC and CRPC PDXs using mass spectrometry. Histone PTM patterns were subcategorized based on common genetic alterations found in PC. RNA-sequencing data for the PDXs and publicly available human PC datasets were used to further characterize HMEs. Co-expression of CHD1, NSD2, and other HMEs was examined in human PC tissue microarrays (TMAs). CHD1 KO clones were generated using CRISPR and levels of histone PTMs and HMEs were assessed and quantified. Gene set enrichment analysis (GSEA) was performed to determine the pathways altered with CHD1 in CRPC PDXs. Results: A comparison of all PDX tumors revealed increased H3K14 and H4 acetylation in CRPC tumors relative to paired HSPC derivatives. We also observed distinct histone PTM patterns associated with common genetic alterations. When compared to tumors with CHD1 WT, tumors with CHD1 loss develop reduced histone PTM H3.3K36me2. CHD1 is a chromatin remodeler commonly deleted in ~ 15% of primary PCs. Screening the differential expression and activity of HMEs in these PDXs reveals that HME NSD2 correlates with CHD1. The human CRPC SU2C/PCF dataset shows a strong positive correlation between CHD1 and NSD2 mRNA (r=0.44). Human CRPC TMAs show decreased protein expression of NSD2 and its histone mark H3K36me2 is associated with reduced CHD1 levels. CHD1 KO in DU145 results in a loss of H3.3K36me2 and a 0.5-fold decrease in NSD2 expression. GSEA revealed that a reduction in the DNA repair pathway is associated with CHD1 loss. The CRPC PDXs (n=24) and human dataset SU2C/PCF 2019 showed a strong positive correlation between CHD1, NSD2, and DNA damage repair genes. Conclusions: We have identified for the first time that genetic alterations alter histone marks during the transition to castration-resistant cancer. Reduced histone H3.3K36 methylation is associated with the genetic loss of CHD1 during the transition to CRPC. The expression of NSD2 is altered in the CRPC state in a CHD1 status-dependent manner. The CHD1-NSD2 phenotype may be the target of novel therapeutic drug combinations – the subject of ongoing research. Citation Format: Tanaya A. Purohit, Joseph Gawdzik, Bing Yang, Eric A. Armstrong, Peter W. Lewis, John M. Denu, David F. Jarrard. Genetic alterations induce distinct histone post-translational modifications during the transition to castration-resistant prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A060.