Papillary thyroid cáncer-driving oncogene BRAFV600E induces Toll-like receptor 4 overexpression

PEYRET V; NAZAR, M; NICOLA JP; FUZIWARA CS; MONTESINOS, MM; PELLIZAS CG; KIMURA ET; MASINI-REPISO AM

Orlando

Congreso; 15th International Thyroid Congress (ITC); 2015

American Thyroid Association

Introduction: Toll like receptors (TLRs) comprise a family of transmembrane proteins related to the Interleukin-1 receptor. Emerging evidence suggests that deregulated TLRs expression in tumor tissue promotes tumor survival signals, thus favoring tumor progression. Recently, aberrant TLR4 overexpression was demonstrated in papillary thyroid cancer (PTC). Aim: To study the mechanisms underlying TLR4 overexpression in PTC harboring the BRAFV600E mutation. Methods / Case Presentation: TLR4 expression was evaluated in thyroid tissue derived from human PTCs and transgenic mice expressing BRAFV600E in thyrocytes (Tg-BRAFV600E mice) (immunohistochemistry and RT/qPCR). PCCl3 cells expressing BRAFV600E in response to doxycycline (PC-BRAFV600E) and BRAFV600E-positive PTC cell line BCPAP were used to study BRAFV600E-driven TLR4 expression (western blot, RT/qPCR, and gene reporter assays). Results / Discussion: Immunohistochemistry analysis showed TLR4 overexpression in primary and metastatic human PTCs compared to normal thyroid tissue. Moreover, TLR4 expression was increased in thyroid tissue from Tg-BRAFV600E mice compared to littermate controls. Stimulation of doxycycline-treated PC-BRAFV600E and BCPAP cells with the TLR4 agonist lipopolysacharide induced the activation of the transcription factor NF-?B (5X NF?B-Luciferase reporter), suggesting functional TLR4 signaling. Doxycycline-induced BRAFV600E expression in PC-BRAFV600E cells upregulated TLR4 protein levels. BRAFV600E increased TLR4 expression at transcriptional level by stimulating TLR4 promoter activity. Deletion analysis of the TLR4 promoter revealed a distal mitogen-activated protein kinase (MAPK)-sensitive ETS binding-site critical for BRAFV600E-induced TLR4 expression. Consistently, pharmacological inhibition of BRAFV600E and MEK/ERK signaling reduced TLR4 mRNA expression in the BRAFV600E-positive PTC cell line BCPAP.Conclusions: Our findings revealed that the oncogene BRAFV600E induces functional TLR4 overexpression in thyroid cancer involving a MEK/ERK-dependent TLR4 gene transcriptional activation. Altogether, these data raise an intriguing question regarding the role of TLR4 signaling in the development and progression of PTC, opening new possibilities for the design of therapeutic approaches.