alpha-Catulin promotes cancer stemness by antagonizing WWP1-mediated KLF5 degradation in lung cancer

Background: The cytoskeletal linker protein alpha-Catulin has been shown to be important for tumor progression in various cancers. However, its role in the regulation of cancer stemness remains unclear. Methods: Phenotypic effects of alpha-Catulin on the cancer stem cell (CSC)-like properties and metastasis were examined by in vitro sphere formation assay, migration assay, invasion assay, and in vivo xenografted animal models. Yeast two-hybrid assay, co-immunoprecipitation assay, and cycloheximide chase assay were performed to confirm the effect of alpha-Catulin on the WWP1-mediated degradation of KLF5. CPTAC and TCGA database were analyzed to determine the clinical association of alpha-Catulin, KLF5, and stemness-associated signatures in lung adenocarcinoma. Results: We report that alpha-Catulin increases cancer stem-like properties in non-small cell lung cancer (NSCLC). The expression of alpha-Catulin is elevated in tumor spheres compared to sphere-derived adherent cells and promotes the acquisition of cancer stemness characteristics in vitro and in vivo. Mechanistically, the interaction of alpha-Catulin and the C-terminal region of Kruppel-like transcription factor KLF5 results in the inhibition of WWP1-mediated degradation of KLF5. Accordingly, increased protein expression of KLF5 is observed in clinical specimens of lung adenocarcinoma with high expression of alpha-Catulin compared to specimens with low alpha-Catulin-expression. Knockdown of KLF5 abrogates alpha-Catulin-driven cancer stemness. alpha-Catulin is known to interact with integrin-linked kinase (ILK). Notably, an ILK inhibitor disrupts the alpha-Catulin-KLF5 interaction, promotes the degradation of KLF5, and decreases alpha-Catulin-driven cancer stemness. Importantly, we identify a CTNNAL1/ILK/KLF5 three-gene signature for predicting poor overall survival in patients with lung adenocarcinoma. Conclusions: These findings reveal a molecular basis of alpha-Catulin-enhanced KLF5 signaling and highlight a role for alpha-Catulin in promoting cancer stemness.