Abstract 2574: An exon-skipping HDAC1 novel isoform promotes colorectal carcinogenesis

Abstract Introduction: In a recent profiling for alternative splicing variants in patient-derived colorectal cancer (CRC) organoids by long-read SMRT sequencing, we identified a hitherto undescribed in-frame spliced transcript of HDAC1 with exon 7 skipping (HDAC1-ΔEx7). This study aims to explore the potential role of HDAC1-ΔEx7 in colorectal carcinogenesis. Methods: Quantitative PCR was performed to evaluate the expression of HDAC1 canonical and HDAC1-ΔEx7 isoforms in a cohort of CRC patient (n=103). Functional biology of HDAC1-ΔEx7 was studied in colon organoids and in vivo model. RNA sequencing was carried out for mechanistic investigation. Results: HDAC1-ΔEx7, but not the full-length HDAC1, showed significant upregulations in CRC tumors compared to matching adjacent non-tumoral tissue (p < 0.0001). Change in HDAC1-ΔEx7 expression was not observed in gastric, hepatocellular and esophageal cancer, suggesting HDAC1-ΔEx7 might be exclusive to CRC. The increased HDAC1-ΔEx7 expressions could draw significant associations with inferior patients’ survivals and likely represent an independent prognostication tumor biomarker. Our functional studies highlighted that HDAC1 full-length and HDAC1-∆Ex7 had distinct biological consequences in CRC. Overexpression of HDAC1-ΔEx7 could induce malignant features of non-tumoral colon organoids, including transforming the single layer-luminal non-tumoral organoids into cancerous organoids with compact and multi-layer cell cluster structure, and increasing the ability of organoids’ long-term propagation. In addition, HDAC1-ΔEx7 could trigger anchor-independent spheroid formation in CRC cell line and protect against stress induced cell death. Investigation of metastatic potential of HDAC1 isoforms in BALB/c nude mice indicated that HDAC1-ΔEx7, but not canonical, substantially increased lung metastatic burden with respect to both lesions size and numbers. Our mechanistic investigation highlighted a unique role of HDAC1-ΔEx7 in protecting CRC against ferroptosis induced cell death. Overexpression of HDAC1-ΔEx7 significantly scavenged the lipid ROS induced by glutamate and inhibited ferroptosis hallmark genes expression. Re-expression of HDAC1-ΔEx7 upon CRISPR-based knocked out of endogenous HDAC1 could robustly rescue CRC against ferroptosis induced from Erastin. Transcriptome revealed that HDAC1-ΔEx7 overcomes ferroptosis through regulating ion homeostasis. Conclusion: Our study identified a novel exon 7 skipping isoform of HDAC1 in CRC and showed its oncogenic role in promoting CRC carcinogenesis through inferring resistance to ferroptosis. Citation Format: Guangzheng Deng, Yujuan Dong, Zhongxu Zhu, Yue Guo, Xin Wang, Simon Ng, Nathalie Wong. An exon-skipping HDAC1 novel isoform promotes colorectal carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2574.