A TBX2-Driven Signaling Switch from Androgen Receptor to Glucocorticoid Receptor Confers Therapeutic Resistance in Prostate Cancer

Abstract Text Background Recent research reveals that glucocorticoid receptor (GR) activation induces enzalutamide resistance in advanced prostate cancer (PCa) by bypassing androgen receptor (AR) signaling, yet the underlying molecular mechanisms remain elusive. Our previous findings identified TBX2, a T-box transcription factor, as overexpressed in castration-resistant PCa (CRPC). Recent reports confirm TBX2 and GR as key drivers of enzalutamide resistance. Our study elucidates TBX2's role as a molecular switch, repressing AR levels while activating GR expression, thus substituting AR signaling and promoting tumor growth. Methods We genetically modulated TBX2 using multiple approaches: a) dominant negative, DN, to block TBX2 (TBX2DN), and b) overexpression, OE, to increase TBX2 expression (TBX2OE), c) shRNA mediated knockdown (shTBX2). RNA-seq, qRT-PCR, Western blot and IHC were performed. Further, we used ChIP, SDM and Co-IP was used. Results TBX2 binds to AR and GATA2 promoters, exerting bimodal repression on AR expression. Conversely, TBX2 upregulated GR via direct GR promoter binding and protein-protein interaction. Together, concurrent repression of the AR and activation of GR resulted in enzalutamide resistance. Notably, SP2509, an LSD1 inhibitor, disrupts TBX2-LSD1 and TBX2-GR interactions, revealing a novel mechanism for SP2509 in CRPC. Our findings support a model where TBX2, LSD1 and GR proteins interact, and pharmacological inhibition of LSD1 impedes the TBX2-driven AR-to-GR switch by disrupting TBX2-GR interaction. Conclusions In summary, our study identifies TBX2 as the molecular switch that drives the AR to GR signaling bypass thereby conferring enzalutamide resistance. Further, our study provides key insights into a potential therapeutic modality for targeting the AR to GR signaling switch via disruption of the TBX2-LSD1 and TBX2-GR protein-protein interactions. Date of Presentation October 16, 2024