| Summary: | Background & Aims: Lysosome-associated protein transmembrane 4β (LAPTM4B) is an oncogene implicated in the malignant progression of hepatocellular carcinoma (HCC). Previous research established a strong association between LAPTM4B and HCC stemness. However, specific mechanisms by which LAPTM4B regulates and maintains the stemness of liver cancer stem cells remain unclear. Therefore, we investigated the effects of LAPTM4B on the stemness regulation of cluster of differentiation 133 (CD133)+ liver cancer stem-like cells (CSLCs). Methods: We used RNA interference and overexpression techniques in both in vitro and in vivo models. The involvement of LAPTM4B in wingless/integrated (WNT)/β-catenin signaling was examined through western blotting, immunofluorescence, and immunoprecipitation. The impact of LAPTM4B on β-catenin phosphorylation and ubiquitination was analyzed to elucidate its role in promoting stemness. Clinical relevance was evaluated in an in-house cohort of 105 specimens from patients with HCC through immunohistochemical and microarray analysis, enabling investigation of correlations with clinical outcomes. Results: LAPTM4B promoted the self-renewal ability, chemoresistance, and tumorigenicity of CD133+ CSLCs. Mechanistically, aberrant LAPTM4B upregulation facilitated β-catenin nuclear translocation (nucleocytoplasmic separation assay, p <0.001) and inhibited its phosphorylation (p <0.01). In addition, LAPTM4B interacts with the deubiquitinating enzymes ubiquitin carboxyl-terminal hydrolase (USP)-1 and USP14, reducing β-catenin ubiquitination. Furthermore, patients with high LAPTM4B and β-catenin expression had markedly shorter 3-year overall survival rate (42.9% vs. 74.4%; hazard ratio, 5.174; 95% CI 2.280–11.741, p <0.001). Conclusions: LAPTM4B promotes CD133+ CSLC stemness by activating WNT/β-catenin signaling by inhibiting β-catenin phosphorylation and ubiquitination degradation. The role of LAPTM4B in regulating WNT/β-catenin signaling suggests that LAPTM4B serves as a therapeutic target for impairing HCC stemness and progression. Impact and implications: LAPTM4B contributes significantly to CD133+ CSLC stemness and inhibits β-catenin phosphorylation and ubiquitination degradation, activating WNT/β-catenin signaling. WNT inhibitors suppress LAPTM4B-induced CD133+ CSLC stemness. Thus, targeting the LAPTM4B–WNT/β-catenin axis could improve antitumor efficacy.
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