BRAF super(V600E) Promotes Invasiveness of Thyroid Cancer Cells through Nuclear Factor Kappa B Activation

The BRAF super(V600E) mutation is closely linked to tumorigenesis and malignant phenotype of papillary thyroid cancer. Signaling pathways activated by BRAF super(V600E) are still unclear except a common activation pathway, MAPK cascade. To investigate the possible target of BRAF super(V600E), we developed two different cell culture models: 1) doxycycline-inducible BRAF super(V600E)-expressing clonal line derived from human thyroid cancer WRO cells originally harboring wild-type BRAF; 2) WRO, KTC-3, and NPA cells infected with an adenovirus vector carrying BRAF super(V600E). BRAF super(V600E) expression induced ERK phosphorylation and cyclin D1 expression in these cells. The BRAF super(V600E)-overexpressing cells also showed an increase of nuclear factor Kappa B (NF- Kappa B) DNA-binding activity, resulting in up-regulation of antiapoptotic c-IAP-1, c-IAP-2, and X-linked inhibitor of apoptosis. Furthermore, BRAF super(V600E) expression also induced the expression of matrix metalloproteinase and cell invasion into matrigel through NF- Kappa B pathway. Increased invasive ability by BRAF super(V600E) expression was significantly inhibited by a specific NF- Kappa B inhibitor, racemic dehydroxymethylepoxyquinomicin. These data indicate that BRAF super(V600E) activates not only MAPK but also NF- Kappa B signaling pathway in human thyroid cancer cells, leading to an acquisition of apoptotic resistance and promotion of invasion. Inactivation of NF- Kappa B may provide a new therapeutic modality for thyroid cancers with BRAF super(V600E).