Abstract LB-A13: LSD1 activates both PI3K/AKT and AR signaling in prostate cancer cells

Background: Lysine specific demethylase 1 (LSD1/KDM1A), a specific demethylase of mono- or di-methylated histone lysine 4 (H3K4me1,2, enhancer-associated signature), was first identified as a component of REST repressor complex composed of CoREST and histone deacetylases 1, 2 (HDAC1,2). In hematopoietic malignancies, targeting LSD1 has shown very promising clinical outcomes, potentially through promoting myeloid differentiation. In solid tumors, multiple mechanisms have been proposed for the antitumor effect of inhibiting LSD1. While LSD1 is well known for its transcription repressor activity, it also activates gene transcription through demethylating repressive histone marks, such as H3K9me1,2, and possibly other non-histone proteins. In particular, LSD1 functions as a major androgen receptor (AR) coactivator in prostate cancer (PCa) cells. Indeed, we reported that LSD1 interacts and colocalizes with FOXA1, a pioneer factor of AR, at AR-mediated enhancers, and this interaction may facilitate AR transcription activity. Nonetheless, since AR signaling is critical to PCa development and progression to the lethal stage of castration-resistant PCa (CRPC), studies from us and others highly suggest that targeting LSD1 may be a potential treatment strategy for CRPC, where AR signaling is commonly restored. However, whether LSD1 regulates other major tumor-promoting pathways in PCa cells remains to be determined. Identification of suchcritical LSD1 targets will provide important insights for developing more effective therapeutic strategy for treating PCa. Experiments and Results: To address this question, we conducted RNA-seq analyses of LSD1 inhibitor treated PCa cells. We first confirmed that prolonged LSD1 inhibitor treatment in the presence of androgens broadly impaired AR transcriptional output. Importantly, we found that the LSD1 inhibitor repressed genes were also enriched for PI3K/AKT pathway even in absence of androgen stimulation. We further confirmed that LSD1 inhibition and Knock-out significantly decreased AKT phosphorylation, which interestingly is independent of AR signaling, as targeting LSD1 also decreased AKT phosphorylation in AR negative PCa cells. Through functional annotation analyses and subsequent validations, we identified the regulatory subunit of PI3K, p85α and possibly its isoform p85β, as a critical transcriptional target of LSD1 that mediates its effect on PI3K/AKT pathway activation. Using a combined analysis with ChIP-seq against LSD1 and H3K4me2, we identified a regulatory region on the PIK3R1 gene loci that may be responsible for regulating its gene transcription. We further investigated the effect of LSD1 inhibitor treatment in LuCaP35CR, a patient-derived CRPC xenograft model which is TMPRSS2-ERG positive and PTEN-negative. Using this model, we found that targeting LSD1 impaired the tumor growth and suppressed PI3K/AKT signaling. Conclusion: our study suggests that LSD1 has dual functions in promoting PCa development: 1) it enhances AR signaling through its coactivator function, 2) it activates PI3K/AKT signaling through increasing p85 gene expression. Based on these findings, it is plausible that the effectiveness of LSD1 inhibitor treatment in CRPC may be due to inhibition of both AR signaling and PI3K/AKT signaling pathways. As LSD1 inhibitors are currently being tested in phase II clinical trials of leukemia, our studies can be rapidly translated into clinical trials of CRPC. Citation Format: zifeng wang, Shuai Gao, Changmeng cai. LSD1 activates both PI3K/AKT and AR signaling in prostate cancer cells [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A13. doi:10.1158/1535-7163.TARG-19-LB-A13