Beyond transcription, RNA molecules are enzymatically modified to influence the biological functions of living organisms. The term “epitranscriptomics” describes the changes in RNA strands aside from altering the innate sequences. Modifications on adenosine (A) are the most widely characterized epitranscriptomic modification, including N6-methyladenosine (m6A), N1-methyladenosine (m1A), polyadenylation, and adenosine-to-inosine (A-to-I) RNA editing, and modifications on other nucleotides seem to be fewer, such as N7-methylguanosine (m7G), 5-methylcytosine (m5C), and pseudouridine (Ψ). These changes on the RNA strand surface, exclusively by their RNA-modifying proteins (RMPs), are reported in various biological phenomena, including programmed cell death (PCD). One necro-biological phenomenon that has been observed for long but has started to gain heed in recent years is “ferroptosis.” The phospholipid peroxidation by polyunsaturated-fatty-acid-containing-phospholipid hydroperoxyl (PLOOH) radicals destroys membrane integrity due to a series of mechanisms. The Fenton reaction, constituting the final Haber–Weiss reaction that is less recognized, collaboratively leading to the conversion of polyunsaturated fatty acid (PUFA) to PLOOH, is the etymological origin of ferroptosis. However, it is with increasing evidence that ferroptotic signaling is also intervened by epitranscriptomic modifications, although the truth is still ambiguous. We attempted to delineate some up-to-date discoveries on both epitranscriptomics and ferroptosis, bringing up the fundamentals to address any potential connection between the two. Next, we discussed whether a duologal relationship, or more, exists between the two, taking the ROS level and iron status into consideration. Lastly, we surveyed future perspectives that would favor the understanding of these topics.

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.