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. Although inducible nitric oxide synthase (iNOS) is a crucial regulator of cancer development and progression, its roles in epithelial-mesenchymal transition (EMT) and the path-ogenesis of metastatic colorectal cancer have not been fully inves-tigated. Primary colorectal cancer and liver metastatic tissue speci-mens were analyzed showing 90% of liver metastatic colorectal cancer with reduced expressions of iNOS compared with 6% of primary colorectal cancer. The Cancer Genome Atlas database analyses via cBioPortal reveal that mRNA expression of iNOS negatively correlated with selected EMT markers in colorectal cancer in a cancer type-dependent manner. The transcriptomic profiling (RNA sequencing data) indicates that iNOS knockdown in SW480 colorectal cancer 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 mem-brane to cytoplasm through iNOS-GATA4-Crb2-E-cadherin path-way. 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 patients with colorectal cancer.