CSN3 promotes colorectal cancer cell progression through activation of the PI3K/AKT/mTOR pathway.

BACKGROUND: CSN3 (κ-casein) is essential for casein micelle formation and cellular differentiation, and dysregulated CSN3 has been linked to tumorigenesis. However, its role in colorectal cancer (CRC) remains unclear.

METHODS AND RESULTS: CSN3 expression in CRC was evaluated using GEO and TCGA datasets, immunohistochemistry, and qRT-PCR. Its biological functions were investigated using gain- and loss-of-function approaches combined with CCK-8, apoptosis, wound-healing, and Transwell assays. Transcriptomic analysis of the GEO dataset GSE21510 was used to identify CSN3-associated signaling pathways, which were further investigated by western blotting, RT-qPCR, co-immunoprecipitation (Co-IP), AKT inhibition, and CSN1S1 knockdown rescue experiments. CSN3 was significantly upregulated in CRC tissues and was associated with lymph node metastasis, advanced TNM stage, and poor prognosis. Functionally, CSN3 overexpression promoted CRC cell proliferation, migration, and invasion while suppressing apoptosis, whereas CSN3 knockdown produced the opposite effects. CSN3 also promoted epithelial-mesenchymal transition (EMT). Mechanistically, enrichment analysis and western blotting demonstrated that CSN3 activated the PI3K/AKT/mTOR signaling pathway, accompanied by increased phosphorylation of PI3K, AKT, mTOR, p70S6K, and 4EBP1. MK-2206 attenuated CSN3-induced proliferation, migration, invasion, and EMT, partially restored apoptosis, and reduced AKT phosphorylation. STRING and Co-IP supported an association between CSN3 and CSN1S1. CSN1S1 knockdown attenuated CSN3-induced proliferation, migration, invasion, EMT, and AKT activation.

CONCLUSIONS: CSN3 promotes malignant CRC cell phenotypes partly through AKT signaling, with CSN1S1 contributing to CSN3-mediated AKT activation and tumor-promoting effects, suggesting potential prognostic relevance in CRC.