Increased CYP24A1 expression is associated with BRAF V600E mutation and advanced stages in papillary thyroid carcinoma.

Objective 1α, 25( OH)2D3 (calcitriol), the active form of vitamin D, has been shown to exert antiproliferative effects in many cancers. Overexpression of CYP24A1, the primary vitamin D-inactivating enzyme, is also observed in a variety of human cancers, thus potentially neutralizing the antitumour effect of 1α, 25( OH)2D3. This study investigates the expression of CYP24A1 and the effect of BRAF V600E on its expression in thyroid cancer. Methods We investigated 60 papillary thyroid carcinoma ( PTC) specimens for CYP24A1 expression and its association with BRAF mutation and disease progression. CYP24A1 expression was measured by real-time RT- PCR, and BRAF V600E mutation was detected by PCR- DNA sequencing analysis. The interaction between BRAF V600E and CYP24A1 expression was determined by Western blot analysis and real-time RT- PCR. Results CYP24A1 expression was increased in PTC as compared to benign multinodular goitre. The expression was further increased in stage III and IV tumours. There is a strong correlation between CYP24A1 overexpression and BRAF V600E mutation ( P < 0·01). In thyroid cancer cell lines expressing BRAF V600E, CYP24A1 expression was significantly higher when compared to those without BRAF V600E expression. BRAF V600E transgene expression in CAL62 cell line can induce CYP24A1 expression. Furthermore, BRAF V600E inhibitor PLX4720 can significantly down-regulate CYP24A1 expression and enhance the antiproliferative effects of calcitriol in thyroid cancer cell lines. Conclusion CYP24A1 overexpression is a poor prognostic indicator for PTC and may reflect BRAF V600E mutation and MARK activation. The crosstalk between vitamin D and MAPK signalling pathways results in resistance to calcitriol-mediated antitumour effects, and the resistance can be reversed by BRAF V600E inhibitor PLX4720. [ABSTRACT FROM AUTHOR]