Abstract

BACKGROUND: BRAF mutation is the most common somatic mutation in thyroid cancer. The mechanism associated with BRAF mutant tumor aggressiveness remains unclear. Lysyl oxidase (LOX) is highly expressed in aggressive thyroid cancers, and involved in cancer metastasis. The objective is to determine whether LOX mediates the effect of the activated MAPK pathway in thyroid cancer.METHODS: The prognostic value of LOX and its association with BRAF mutation was analyzed in the TCGA and an independent cohort. Inhibition of mutant BRAF and the MAPK pathway, and overexpression of BRAF mutant and mouse models of BRAFV600E were used to test the effect on LOX expression.RESULTS: In the TCGA cohort, LOX expression was higher in BRAF mutant tumors compared to wild-type tumors (P<0.0001).Patients with BRAF mutant tumors with high LOX expression had a shorter disease-free survival (DFS) (P=0.03) compared to patients with BRAF mutation and low LOX group. In the independent cohort, a significant positive correlation between LOX and percentage of BRAF mutated cells was found. The independent cohort confirmed high LOX expression to be associated with a shorter DFS (P=0.01). Inhibition of BRAFV600E and MEK decreased LOX expression. Conversely overexpression of mutant BRAF increased LOX expression. The mice with thyroid-specific expression of BRAFV600E, showed a strong LOX and p-ERK expressions in tumor tissue. Inhibition of BRAFV600E in transgenic and orthotopic mouse models significantly reduced the tumor burden as well as LOX and p-ERK expressions.CONCLUSIONS: Our data suggests that BRAFV600E tumors with high LOX expression are associated with more aggressive disease. The biological underpinnings of the clinical findings were confirmed by showing that BRAF and the MAPK pathway regulate LOX expression.

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