SF3B3-dependent inclusion of STOX1 exon 3 facilitates invasion and tumor progression in colorectal cancer.

Alternative splicing dysregulation contributes to colorectal cancer (CRC) progression, yet the roles of specific splicing factors, such as SF3B3, remain poorly defined. To identify key dysregulated splicing factors, RNA sequencing was performed comparing high-metastatic (SW620) and low-metastatic (SW480) CRC cell lines. Notably, SW480 and SW620 are isogenic cell lines derived from the primary tumor and lymph node metastasis of the same CRC patient, respectively. Their consistent genetic background minimizes confounding factors, enabling reliable detection of metastasis-associated molecular alterations. Functional assays-including MTT, wound healing, and transwell experiments-combined with molecular analyses confirmed the critical role of the SF3B3-STOX1 axis. SF3B3 was markedly upregulated in metastatic CRC cells and patient tissues. Mechanistically, SF3B3 promoted CRC cell proliferation, migration, and invasion by modulating STOX1 alternative splicing, specifically enhancing exon 3 inclusion to produce the oncogenic isoform STOX1-L while suppressing STOX1-S. Notably, STOX1-L, but not STOX1-S, robustly activated the PI3K-AKT and MAPK/ERK signaling pathways. Importantly, knockdown of STOX1-L reversed the malignant phenotypes driven by SF3B3. Collectively, these results identify SF3B3 as a pivotal regulator of CRC cell metastasis in the isogenic SW480/SW620 cell model that acts through the production of STOX1-L, establishing the SF3B3-STOX1-L axis as a promising candidate therapeutic target for advanced colorectal cancer worthy of further validation in diverse CRC models.