BRAFV600E mutation, TIMP-1 up-regulation and NF-{kappa}B activation: closing the loop on the papillary thyroid cancer trilogy.

Abstract

BRAFV600E is the most common mutation found in papillary thyroid carcinoma (PTC). Tissue inhibitor of metalloproteinases (TIMP-1) and nuclear factor (NF)-kB have been shown to play an important role in thyroid cancer. In particular, TIMP-1 binds its receptor CD63 on cell surface membrane and activates Akt signaling pathway, which is eventually esponsible for its antiapoptotic activity. The aim of our study was to evaluate whether interplay among these three factors exists and exerts a functional role in PTCs. To this purpose, 56 PTC specimens were analyzed for BRAFV600E mutation, TIMP-1 expression, and NF-kB activation. We found that BRAFV600E mutation occurs selectively in PTC nodules and is associated with hyperactivation of NF-kB and upregulation of both TIMP-1 and its receptor CD63. To assess the functional relationship among these factors, we first silenced BRAF gene in BCPAP cells, harboring BRAFV600E mutation. We found that silencing causes a marked decrease in TIMP-1 expression and NF-kB binding activity, as well as decreased invasiveness. After treatment with specific inhibitors of MAPK pathway, we found that only sorafenib was able to increase IkB-a and reduce both TIMP-1 expression and Akt phosphorylation in BCPAP cells, indicating that BRAFV600E activates NF-kB and this pathway is MEK-independent. Taken together, our findings demonstrate that BRAFV600E causes upregulation of TIMP-1 via NF-kB. TIMP-1 binds then its surface receptor CD63, leading eventually to Akt activation, which in turn confers antiapoptotic behavior and promotion of cell invasion. The recognition of this functional trilogy provides insight on how BRAFV600E determines cancer initiation, progression, and invasiveness in PTC, also identifying new therapeutic targets for the treatment of highly aggressive forms.