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

PEYRET VICTORIA, NAZAR MAGALÍ, NICOLA JUAN PABLO, FUZIWARA CESAR SEIGI, KIMURA EDNA TERUKO, MONTESINOS MARÍA DEL MAR, PELLIZAS CLAUDIA GABRIELA, MASINI - REPISO ANA MARÍA.

Orlando, Florida

Congreso; 15th International thyroid Congress (15th 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 tissuepromotes 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 BRAFB600E mutation.Methods / Case Presentation: TLR4 expression was evaluated in thyroid tissue derived from human PTCs and transgenic mice expressing BRAFB600E in thyrocytes (Tg-BRAFB600E mice) (immunohistochemistry andRT/qPCR). PCCl3 cells expressing BRAFB600E in response to doxycycline (PCBRAFB600E)and BRAFB600E positive PTC cell line BCPAP were used to study BRAFB600E 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 TgBRAFB600E mice compared to littermate controls.Stimulation of doxycycline treated PCBRAFB600E and BCPAP cells with the TLR4 agonist lipopolysacharide induced the activation of the transcription factor NFkappaB (5X NFkappaB Luciferase reporter), suggesting functional TLR4 signaling.Doxycycline-induced BRAFB600E expression in PCBRAFB600E cells upregulated TLR4 protein levels. BRAFB600E increased TLR4 expression at transcriptional level by stimulating TLR4 promoter activity. Deletionanalysis of the TLR4 promoter revealed a distal mitogen activatedprotein kinase (MAPK)sensitive ETS binding site critical for BRAFB600E induced TLR4 expression. Consistently, pharmacological inhibition ofBRAF and MEK/ERK signaling reduced TLR4 mRNA expression in the BRAFB600E positive PTC cell line BCPAP.Conclusions: Our findings revealed that the oncogene BRAFB600E induces functional TLR4 overexpression in thyroid cancer involving a MEK/ERK dependent TLR4 gene transcriptional activation. Altogether, these dataraise 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.