FUBP3-Mediated Recruitment of STAT3 Complex Formation to Activate EMT Factor Twist1 and Promote Lung Cancer Metastasis.

[BACKGROUND] Lung cancer is the leading cause of cancer-related mortality worldwide, and metastasis is the key factor leading to patient death. Epithelial-mesenchymal transition (EMT), which is crucial to tumor metastasis, is primarily regulated by EMT transcription factors, such as Twist1. As an RNA-binding protein, far upstream element binding protein 3 (FUBP3) shows aberrant expression in various tumors; however, its mechanistic role in lung cancer metastasis remains unclear. This study aims to elucidate the functional role of FUBP3 in lung cancer metastasis and its molecular mechanism in the regulation of Twist1.

[METHODS] Bioinformatics analysis was conducted to examine FUBP3 expression patterns in lung cancer and its association with patient prognosis. The Cancer Genome Atlas database was used, and FUBP3 protein expression levels were detected in clinical lung cancer tissues by immunohistochemical analysis. Lung cancer cell lines with FUBP3 knockdown were established, and the effects of FUBP3 on the metastatic capacity of lung cancer were assessed using Transwell migration and invasion assays, 3D spheroid invasion experiments, and tail vein injection metastasis models. Changes in the expression levels of EMT markers were detected by western blot, quantitative real-time polymerase chain reaction, and immunofluorescence. The interaction between FUBP3 and signal transducer and activator of transcription 3 (STAT3) was verified by co-immunoprecipitation (Co-IP), proximity ligation assay, and immunofluorescence co-localization. The effects of STAT3 inhibitor S3I-201 on FUBP3-mediated pro-metastatic functions were assessed.

[RESULTS] Bioinformatics analysis revealed high FUBP3 expression in lung cancer tissues, which correlated with poor patient prognosis. Notably, patients with distant metastasis (M1) stage exhibited higher FUBP3 expression than those at the no distant metastasis (M0) stage. Functional experiments confirmed that FUBP3 silencing inhibited the migration and invasion of lung cancer cells, as well as the formation of pulmonary metastatic foci . The knockdown of FUBP3 led to an increase in the expression of the epithelial marker E-cadherin and downregulated the expression of the mesenchymal marker vimentin, indicating that FUBP3 promotes lung cancer metastasis by promoting EMT. Subsequent analysis indicated that FUBP3 facilitates lung cancer progression by upregulating Twist1 expression. Both exhibit positive correlations in lung cancer patient tissues. Co-IP and immunofluorescence assays demonstrated a direct interaction between FUBP3 and STAT3 proteins. STAT3 silencing counteracted pro-metastatic effects associated with FUBP3 overexpression in lung cancer metastasis. Treatment with S3I-201 effectively reversed the pro-metastatic phenotype in cells with high FUBP3 expression, restored the typical patterns of EMT marker expression, and reduced the formation of metastatic foci in the metastasis model.

[CONCLUSION] This study reveals the critical role of FUBP3 in lung cancer metastasis and identifies a new regulatory axis involving FUBP3-STAT3-Twist1. FUBP3 interacts with STAT3, enhancing STAT3-dependent Twist1 expression, which promotes EMT and metastasis. FUBP3 functions as a prognostic biomarker, and STAT3 inhibitors present therapeutic strategies for lung cancer, offering novel insights for precision treatment.