DP-103

Structural analysis of nuclear receptor subfamily V orphan nuclear receptors suggests that ligand-independent mechanisms must regulate this subclass of receptors. Here, we report that steroidogenic factor 1 (SF-1) and liver receptor homolog 1 are repressed via posttranslational SUMO modification at conserved lysines within the hinge domain. Indeed, mutating these lysines or adding the SUMO isopeptidase SENP1 dramatically increased both native and Gal4-chimera receptor activities. The mechanism by which SUMO conjugation attenuates SF-1 activity was found to be largely histone deacetylase independent and was unaffected by the AF2 corepressor Dax1. Instead, our data suggest that SUMO-mediated repression involves direct interaction of the DEAD-box protein DP103 with sumoylated SF-1. Of potential E3-SUMO ligase candidates, PIASy and PIASxalpha strongly promoted SF-1 sumoylation, and addition of DP103 enhanced both PIAS-dependent receptor sumoylation and SF-1 relocalization to discrete nuclear bodies. Taken together, we propose that DEAD-box RNA helicases are directly coupled to transcriptional repression by protein sumoylation.

Triple-negative breast cancer (TNBC) is a clinically aggressive subtype lacking targeted therapies, often characterized by hyperactivation of the Wnt/β-catenin signaling pathway and an enriched population of cancer stem cells (CSCs). Here, we identify the DEAD-box RNA helicase DP103 as a novel modulator of Wnt/β-catenin signaling in TNBC, acting independently of its canonical helicase function. DP103 expression correlates with increased phosphorylation of LRP6 and nuclear β-catenin accumulation, enhancing Wnt transcriptional activity. Mechanistically, DP103 physically interacts with GSK3β to facilitate post-translational modifications essential for Wnt activation. Notably, DP103 itself is a Wnt target, forming a feedforward loop that sustains oncogenic signaling. Functional studies reveal that DP103 promotes CSC-like traits in TNBC cells, including self-renewal and expression of stemness markers (Nanog, Oct4, Sox2), linking its role in Wnt activation to breast cancer stemness and metastasis. In vivo studies using Drosophila models confirmed the evolutionarily conserved role of Gemin3/DP103 in epithelial transformation, though context-dependent differences were observed. Importantly, we demonstrate that RX-5902, a Wnt pathway inhibitor currently in clinical trials, suppresses DP103 expression and Wnt/β-catenin signaling, reducing TNBC cell viability and mammosphere formation without affecting normal epithelial cells. RX-5902 efficacy was abrogated by DP103 depletion, underscoring DP103’s critical role in mediating drug response. In xenograft models, RX-5902 treatment significantly reduced tumor burden and prolonged survival. Collectively, our findings establish DP103 as a key regulator of Wnt-driven oncogenesis in TNBC and highlight its dual role in promoting CSC traits and therapeutic resistance. These insights position DP103 as a potential biomarker and therapeutic target to disrupt sustained Wnt signaling in TNBC, offering new avenues for precision intervention in this challenging breast cancer subtype.