Abstract 2904: The alternative NF-kB2RELB pathway is activated by LTBLTB receptor and NIK to promote cell migration and metastasis-related gene expression in HNSCC

Head and neck squamous cell carcinomas (HNSCC) are highly inflammatory and preferentially migrate and metastasize to lymph nodes. In this study, we find that LTLTRNIK signaling mediates alternative RELBNF-kB2 activation, which promotes activation of important cancer related genes and migration. We find that LT and LTR are over expressed in subsets of HNSCC tissues and cell lines, and LT activates the alternative NF-B pathway, enhancing nuclear translocation of RELB and NF-kB2p52. Knockdown of LTR decreased its target kinase NIK, and downstream NF-kB subunits RELB and NF-kB2p52 protein expression. Knockdown of NIK protein decreased RELB and p52 protein expression, while LT treatment stabilized NIK, RELB and NF-kB2p52 expression. Consistent with this, knockdown of LTBR and NIK functionally decreased NF-kB reporter gene activity, while treatment of LTB partially restored the NF-kB reporter activity. Notably, knockdown of NIK and RELB by siRNA inhibited cell migration in HNSCC. Since NIK is known as central regulator of the activation of the non-canonical pathway, we tested the effects of a NIK inhibitor 1,32H,4H-Isoquinolinedione on NF-kB function and cell migration. NIK inhibitor decreased NIK protein in the cytoplasm, downstream nuclear expression of RELB and NF-kB2p52 proteins by Western blot and RELB localization by immunofluorescence staining. We have found evidence for LT induction of migrationmetastasis and cell death genes MET, BIRC3,and SERPINE1, and NIK knockdown inhibited cell migration and the inducible expression of MET, BIRC3, SERPINE 1 by LTB. Our data reveal the mechanisms how LT and NIK activation mediated alternative NF-kB pathway and contribute to migration and metastasis of HNSCC.