SLC46A1 deficiency-mediated folate restriction suppresses colorectal cancer progression through epigenetic-transcriptional reprogramming.

The association between folate metabolism abnormalities and the development of colorectal cancer (CRC) remains controversial. Here, we report that the folate exerts a tumor-suppressive role in CRC; however, the manifestation of this effect is restricted by the expression level of folate transporter SLC46A1 in CRC cells. Multi-cohort profiling revealed significant downregulation of SLC46A1 in CRC tissues compared to adjacent normal tissues, where low expression independently predicted poor overall survival. Functional studies demonstrated that SLC46A1-mediated folate uptake suppressed tumor proliferation, migration, and invasion both in vitro and in vivo. Mechanistically, SLC46A1 deficiency restricted intracellular folate availability and impaired cellular methylation potential, as evidenced by a reduced SAM/SAH ratio, leading to DNA hypomethylation at specific sites such as the FOS proto-oncogene promoter. This epigenetic reprogramming triggers transcriptional activation of key oncogenic effectors CCND1, BCL2, and PLAU involved in CRC progression. Clinically, we found a significant inverse correlation between SLC46A1 expression and folate levels in tumor interstitial fluids of CRC, suggesting impaired folate uptake in low SLC46A1 tumors. Multi-color immunofluorescence across two cohorts further demonstrated conserved inverse associations between SLC46A1 and FOS expression in primary tumors and metastatic lesions. This study elucidates the molecular mechanism by which folate inhibits CRC progression through the "SLC46A1-epigenetic-transcriptional regulation" axis, providing mechanistic insights into folate deficiency-driven CRC progression and biomarkers for precision CRC intervention. This study elucidates the tumor-suppressive role of the folate transporter SLC46A1 in CRC. In normal cells, SLC46A1 facilitates folate uptake, supporting one-carbon metabolism and maintaining genomic stability. In CRC, however, SLC46A1 downregulation induces intracellular folate deficiency, triggering locus-specific DNA hypomethylation at the FOS promoter, which activates oncogenic transcription of key downstream effectors (CCND1, BCL2, PLAU), driving tumor progression. The graphical abstract illustrates the differential impact of SLC46A1 on folate metabolism and gene expression in normal versus tumor cells, highlighting its potential as a therapeutic target in CRC.