Downregulation of iNOS/NO promotes epithelial-mesenchymal transition and metastasis in colorectal cancer.

Metastasis is the major cause of cancer-related death in patients with colorectal cancer (CRC). Although inducible nitric oxide synthase (iNOS) is a crucial regulator of cancer development and progression, its roles in epithelial-mesenchymal transition (EMT) and the pathogenesis of metastatic CRC have not been fully investigated. Primary CRC and liver metastatic tissue specimens were analyzed showing 90% of liver metastatic CRC with reduced-expressions of iNOS compared with 6% of primary CRC. TCGA database analyses via cBioPortal reveal that mRNA expression of iNOS negatively correlated with selected EMT markers in CRC in a cancer-type dependent manner. The transcriptomic profiling (RNA-Seq data) indicates that iNOS knockdown in SW480 CRC cells induced an EMT program with upregulated expression of selected stem-cell markers. iNOS knockdown did not alter E-cadherin mRNA expression but re-localized it from membrane to cytoplasm through iNOS-GATA4-Crb2-E-cadherin pathway. iNOS knockdown induced a change in cell morphology, and promoted cell invasion and migration in vitro, and metastasis in vivo. Implications: iNOS downregulation-induced pathway networks mediate the EMT program and metastasis. As an EMT-inducer, the reduced-iNOS may serve as a potential therapeutic target for CRC patients.