Sulfatide Acts as a Regulatory Molecule Controlling β1 Integrin–STAT5 Signaling and BOLA2-Dependent Apoptotic Pathway in Breast Cancer Cells

Cell membrane glycosylations play a critical role in regulating cell signaling, adhesion, and immune recognition. Abnormal glycosylation is a hallmark of cancer and promotes tumor progression. Sulfatide (SM4), a glycosphingolipid synthesized by galactosylceramide sulfotransferase (CST), is frequently altered in cancers, including breast cancer. Our previous studies identified SM4 as an adhesive molecule that enhances metastasis through interactions with platelets and endothelium; however, its elevated levels increase apoptotic sensitivity and reduce tumorigenicity. Here, we elucidate the molecular mechanisms linking sulfatide metabolism to apoptosis and gene regulation. Using MDA-MB-231 and MDA-MB-468 breast cancer cells with altered CST/SM4 levels, RNA sequencing and functional analyses revealed that overproduction of the CST/SM4 significantly downregulated BOLA2, a gene in the CIAPIN1 pathway involved in apoptosis. RT-qPCR and Western blot confirmed an inverse relationship between CST/SM4 and BOLA2. Overexpressing BOLA2 provided resistance to doxorubicin-induced apoptosis, suggesting that SM4-mediated repression of BOLA2 increases apoptotic sensitivity. Luciferase assays showed reduced BOLA2 promoter activity in SM4-enriched cells. Transcription factor profiling and Electrophoretic Mobility Shift Assay demonstrated that SM4 suppresses STAT5 activation, which directly binds and regulates the BOLA2 promoter. SM4 also altered integrin profiles by upregulating β4/β5 and downregulating β1 subunits. Reintroducing β1 integrin restored STAT5 activation and BOLA2 expression, positioning β1 integrin upstream of STAT5. Collectively, these findings identify a novel sulfatide-dependent β1 integrin–STAT5–BOLA2 pathway controlling apoptosis in breast cancer cells. SM4 suppresses β1 integrin and STAT5-mediated BOLA2 transcription, promoting apoptosis, while β4/β5 upregulation may facilitate invasion. This pathway represents a potential therapeutic target in breast cancer.