Abstract 4054: Heme oxygenase 1 and its nuclear interactors: a novel perspective on neuroendocrine prostate cancer

Abstract Heme-oxygenase 1 (HO-1), the rate-limiting enzyme for heme degradation, has been implicated with a non-canonical antitumor role in prostate cancer (PCa). This study addressed the hypothesis that HO-1 exerts its antitumor effects through its protein interactome, aiming to identify HO-1’s nuclear interactors and their potential association with specific PCa phenotypes. PCa cells were treated with hemin (80 µM, 24 h), a specific pharmacological inducer of HO-1, followed by HO-1 immunoprecipitation (IP) and LC-ESI MS/MS analysis, leading to the identification of 42 HO-1 interactors. Since we were interested in the nuclear functions of HO-1 we continue this work focusing in the 11 interactors that appeared only in the nucleui of hemin treated cells. Based on our hypothesis that nuclear HO-1 influences the activity of various transcriptional regulators, ChIP Atlas analysis identified four of 11 interactors—ILF3, DDX17, BCLAF1, and SAFB—as DNA-binding factors with regulomes significantly linked to neurological disorders. To explore the relevance of these interactors in PCa, we analyzed RNA-seq data from the MDA-PCa-PDX series (PCa Patient-Derived Xenografts Program, MD Anderson Cancer Center), which reflects the heterogeneity of PCa. Unsupervised clustering based on the expression of HO-1 interactors revealed that samples with high expression of these genes were predominantly associated with neuroendocrine prostate cancer (NEPC). Further bioinformatics analysis, comprising transcriptomic and clinical data from NEPC patients, demonstrated that the expression of HO-1 interactors distinctly clustered a subgroup of large cell neuroendocrine carcinoma samples characterized by elevated levels of ILF3, DDX17, SAFB, BCLAF1, and low expression of HMOX1. To functionalize these results in vitro, we established a protocol to transdifferentiate C4-2B cells to neuroendocrine (NE) cells using Forskolin (Fsk). Fsk (10uM, 48h) treated cells showed increased expression levels of NE markers namely NSE, EZH2 and SOX2. Also, treatment with Fsk increased neurite-like processes formation, branch points formation and neurite-like processes length, consistent with a NE-like phenotype. In line with the previous bioinformatics analyses, we observed a significant suppression of HMOX1 (p<0.05) expression in NE-like C4-2B cells. Strikingly, this phenotype was accompanied by a significant induction of BCLAF1 (p<0.05) levels, reinforcing its implication in NEPC. Moreover, we confirmed by IP-Western blot HO-1/BCLAF1 physical interaction. In conclusion, our findings suggest that HO-1 exerts its non-canonical antitumor role in PCa by negatively regulating key nuclear interactors, including BCLAF1, ILF3, DDX17, and SAFB. This regulatory mechanism appears to suppress aggressive neuroendocrine phenotypes, particularly in NEPC samples, highlighting its potential as a therapeutic target. Citation Format: Rocio A. Seniuk, Agustina Sabater, Juan Bizzotto, Gaston Pascual, Julia Lechuga, Estefania Labanca, Nicolas Anselmino, Elba Vazquez, Javier Cotignola, Pia Valacco, Geraldine Gueron, Ayelen Toro, Pablo Sanchis. Heme oxygenase 1 and its nuclear interactors: a novel perspective on neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4054.