Olfactomedin 1 negatively regulates NF-kB signalling and suppresses the growth and metastasis of colorectal cancer cells.

Uncontrolled growth and distant metastasis are hallmarks of colorectal cancer (CRC), but the mechanisms are poorly understood. Olfactomedin 1 (OLFM1), a member of the olfactomedin domain-containing protein family, plays an important role in the development of neurogenic tissues. Recently, OLFM1 deregulation was frequently observed in several cancers, and it was induced in colon cell lines after treatment with the demethylating agent 5-aza-2'-deoxycytidine. However, the function of OLFM1 in CRC remains unknown. In this study, we reanalysed published microarray data and found that OLFM1 was significantly downregulated in primary CRC samples compared to adjacent non-cancerous tissues. The results of immunohistochemistry indicated that decreased OLFM1 expression was significantly associated with lymph node status (P=0.023), distant metastasis (P<0.001) and AJCC/TNM stage (p=0.013), and CRC patients with low OLFM1 expression had consistently poor overall survival (OS, p<0.001) and progression-free survival (PFS, p<0.001). Further analysis demonstrated that OLFM1 was epigenetically silenced in CRC tissues and cell lines via promoter hypermethylation. Overexpression and knockdown of OLFM1 attenuated and increased respectively CRC cells' proliferation, migration and invasion in vitro and metastasis to the lung and liver in vivo. Mechanistically, the promotion of growth and metastasis of CRC cells by silencing of OLFM1 was associated with the activation of the non-canonical NF-kB signalling pathway. OLFM1 interacted with NF-kB-inducing kinase (NIK; MAP3K14) and repressed the phosphorylation of its downstream substrate Ikappa B kinase alpha (IKKα). OLFM1 expression was negatively correlated with the phosphorylation level of IKKα in CRC tissue samples. Knockdown of NIK impaired the ability of OLFM1 to repress NF-kB signalling, cell growth or migration. Thus, OLFM1 may be a valuable biomarker and therapeutic target for CRC patients.