BRAFV600E promotes invasiveness of thyroid cancer cells through nuclear factor κB activation

The BRAF(V600E) mutation is closely linked to tumorigenesis and malignant phenotype of papillary thyroid cancer. Signaling pathways activated by BRAF(V600E) are still unclear except a common activation pathway, MAPK cascade. To investigate the possible target of BRAF(V600E), we developed two different cell culture models: 1) doxycycline-inducible BRAF(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(V600E). BRAF(V600E) expression induced ERK phosphorylation and cyclin D1 expression in these cells. The BRAF(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(V600E) expression also induced the expression of matrix metalloproteinase and cell invasion into matrigel through NF-kappa B pathway. Increased invasive ability by BRAF(V600E) expression was significantly inhibited by a specific NF-kappa B inhibitor, racemic dehydroxymethylepoxyquinomicin. These data indicate that BRAF(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(V600E).