In papillary thyroid carcinoma, TIMP-1 expression correlates with BRAF V600E mutation status and together with hypoxia-related proteins predicts aggressive behavior

Abstract

BRAF (V600E) causes upregulation of tissue inhibitor of metalloproteinase-1 (TIMP-1), which promotes cell invasion in papillary thyroid carcinoma (PTC). Hypoxia-inducible factor-1α (HIF- α) is regulated by hypoxia and also by the BRAF-mediated signaling pathway in PTC. We assessed the association of expression of TIMP-1, HIF-1α, and hypoxia-inducible carbonic anhydrase IX (CAIX) and XII (CAXII) with clinical parameters in PTC. TPC-1/BRAF (WT) wild-type and BcPAP/BRAF (V600E) -mutated PTC cell lines were selected to study the effects of the BRAF (V600E) mutation and hypoxia on expression in vitro of TIMP-1, CAIX, and CAXII proteins by immunoblotting. Higher expression of all proteins was detected in BcPAP cells exposed to hypoxia. Tissue microarray immunohistochemistry analysis was performed to study protein expression in 114 BRAF-genotyped PTC samples. Expression data on tumor tissue were compared with clinicopathological variables. TIMP-1 expression had a sensitivity of 87 % and a specificity of 83 % in identifying a BRAF mutation (P < 0.001) and was associated with pT stage (P = 0.001), pN stage (P = 0.02), and multifocality (P = 0.03). HIF-1α expression correlated with pT stage (P = 0.05). CAIX expression was associated with pN stage (P = 0.02), and both CAIX (P = 0.004) and CAXII (P = 0.05) were strongly associated with vascular invasion. We conclude that TIMP-1 protein expression is a reliable surrogate marker for BRAF-mutated status in PTC. TIMP-1 and hypoxia-regulated proteins are promising as predictors of aggressiveness in PTC and warrant further investigation as new therapeutic targets for the treatment of highly aggressive forms of PTC.