NOD1 activation promotes cell apoptosis in papillary thyroid cancer.

[BACKGROUND] NOD1 can promote or inhibit different types of cancers, suggesting that NOD1 functions in the progression of cancers dependent on the tumour environment. However, the expression and mechanisms of NOD1 during papillary thyroid carcinoma (PTC) progression remain unclear.

[METHODS] To investigate the role of NOD1 in PTC development and apoptosis, we detected NOD1 expression in three cell lines and surgical specimens from patients with PTC using immunohistochemistry, quantitative real-time PCR (Q-PCR) and Western blotting; we studied the biological functions of NOD1 by loss-of-function analysis of TPC-1 and BCPAP cells and the effect of NOD1 on the progression of PTC in terms of cell proliferation and apoptosis induced by tumour necrosis factor alpha (TNF-α), Fas ligand (Fas L), tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) or Ala-γGlu-diaminopimelic acid (TriDAP) in the presence of cycloheximide (CHX) and determined its underlying molecular mechanism using PTC cell lines in vitro and mouse xenograft models in vivo.

[RESULTS] Increased expression of NOD1 is correlated with an improved prognosis in thyroid cancer patients. We also found that NOD1 expression was markedly upregulated in PTC cells compared to normal epithelial cells. NOD1 knockdown significantly promoted the proliferation of PTC cells in vitro, while activation of NOD1 signalling promoted PTC cell apoptosis; NOD1-induced apoptosis depends on the activation of caspase-3 and caspase-9 although the RIP2/TAK1 and MAPK pathways in PTC cells.

[CONCLUSIONS] This study demonstrates that NOD1 is a predictive biomarker for PTC and that PTC cell apoptosis is induced by activation of NOD1 via the RIP2/TAK1 and MAPK pathways. The above results may provide a new perspective on targeting NOD1 signalling for the treatment of PTC, which deserves further investigation.