RIPPLY1 as a Guardian Against Cancer Stemness in CTNNB1-Mutated Hepatocellular Carcinoma

Highlight

• RIPPLY1 is transcriptionally activated by the Wnt/β-catenin signaling pathway and significantly upregulated in CTNNB1-mutated hepatocellular carcinoma (HCC).
• Higher RIPPLY1 expression correlates with better prognosis in patients with CTNNB1-mutated HCC.
• Loss of RIPPLY1 increases cancer stemness markers and tumor progression by enhancing TBX19 transcriptional activity.
• RIPPLY1 suppresses TBX19 through recruitment of TLE1 and proteasome-dependent degradation, delineating a novel tumor suppressive mechanism.

Study Background

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths worldwide, with high heterogeneity in its molecular subtypes impacting prognosis and therapeutic response. Mutations in the CTNNB1 gene, which encodes β-catenin, occur frequently in HCC and are notable for their association with well-differentiated tumors exhibiting relatively low stemness features. Despite this clinical observation, the molecular mechanisms mediating this phenotype remain poorly understood. Cancer stemness, a property underlying tumor initiation, progression, resistance to therapy, and relapse, represents a critical target for novel interventions.

RIPPLY1, a transcriptional repressor known for its role in embryonic somitogenesis, has remained largely unexplored within oncology contexts. Investigating whether RIPPLY1 contributes to the distinct biology of CTNNB1-mutated HCC could unveil critical insights for targeted therapies and prognosis.

Study Design

The study employed complementary human tissue analyses and mouse models to elucidate the functional role of RIPPLY1 in CTNNB1-mutated HCC. Human HCC tissue samples with or without CTNNB1 mutations were analyzed for RIPPLY1 expression and clinical correlation. Two genetically engineered mouse models were used: a hepatocyte-specific RIPPLY1 deletion model in a DEN/PB-induced CTNNB1-mutated HCC background, and a hydrodynamic tail-vein injection (HDTVi) model inducing CTNNB1-mutated HCC, enabling in vivo evaluation of RIPPLY1’s role in tumor development and cancer stemness.

Molecular experiments included co-immunoprecipitation, mass spectrometry, and transcriptional activity assays to identify and characterize the interaction between RIPPLY1 and potential target proteins, particularly TBX19. Functional assays assessed cancer stem cell properties upon manipulation of RIPPLY1 and TBX19 levels.

Key Findings

RIPPLY1 Expression and Clinical Correlation: Analysis of human HCC samples revealed that RIPPLY1 is transcriptionally upregulated in tumors harboring CTNNB1 mutations, aligning with activation of the Wnt/β-catenin pathway. Importantly, elevated RIPPLY1 expression correlated with improved overall survival, suggesting RIPPLY1 as a favorable prognostic biomarker within this molecular subgroup.

Functional Role of RIPPLY1 in Tumor Progression: In vivo, hepatocyte-specific deletion of RIPPLY1 significantly promoted tumor initiation and progression in both DEN/PB-induced and HDTVi-mediated CTNNB1-mutated HCC mouse models. This establishes a tumor-suppressive function of RIPPLY1 in this distinct molecular context.

Impact on Cancer Stemness: Loss of RIPPLY1 resulted in upregulation of established stem cell markers and enhancement of cancer stem cell properties, demonstrating that RIPPLY1 restricts the stemness phenotype in CTNNB1-mutated HCC.

Mechanistic Insights – Targeting TBX19: Co-immunoprecipitation combined with mass spectrometry identified TBX19, a T-box transcription factor, as a direct target of RIPPLY1. RIPPLY1 suppresses TBX19 transcriptional activity by recruiting the co-repressor TLE1 and promoting proteasomal degradation of TBX19. Functionally, ablation of TBX19 reversed the increase in cancer stemness induced by RIPPLY1 loss, confirming TBX19 as the critical effector downstream of RIPPLY1.

Expert Commentary

This study elegantly links the transcriptional repressor RIPPLY1 to modulation of cancer stemness through post-translational regulation of TBX19 in CTNNB1-driven HCC. It expands the understanding of how distinct genetic subtypes of HCC can shape tumor differentiation and aggressiveness via specific molecular circuits.

The identification of RIPPLY1 as a suppressor of stemness underscores the complexity of Wnt/β-catenin signaling outcomes, where downstream effectors can act as tumor suppressors despite pathway activation. Targeting TBX19 or enhancing RIPPLY1 function may offer new opportunities for therapeutic intervention aimed at eradicating cancer stem cells and improving outcomes in this subset of HCC patients.

However, the study is primarily preclinical, with mechanistic insights derived from mouse models and molecular assays. Validation in larger and more diverse patient cohorts, as well as exploration of therapeutic feasibility, will be critical next steps.

Conclusion

RIPPLY1 plays a crucial tumor-suppressive role in CTNNB1-mutated hepatocellular carcinoma by repressing cancer stemness. It achieves this through direct interaction with TBX19, leading to TBX19 degradation and inhibition of its transcriptional activity. The loss of RIPPLY1 lifts this repression, augmenting stem cell-like properties, tumor progression, and correlating with poorer prognosis.

This research not only provides novel mechanistic insight into the stemness phenotype of CTNNB1-mutated HCC but also highlights RIPPLY1 and TBX19 as potential biomarkers and therapeutic targets. Advancing understanding of this axis may enable development of more tailored treatment strategies to improve patient outcomes in CTNNB1-driven liver cancer.

Funding and Clinicaltrials.gov

The original study was published in Hepatology (2025) supported by institutional research grants. No registered clinical trials were referenced related to RIPPLY1 or TBX19 modulation in HCC.

References

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