Functional Toll-like Receptor 4 Overexpression in Papillary Thyroid Cancer by MAPK/ERK–Induced ETS1 Transcriptional Activity
Molecular Cancer Research
32 Emerging evidence suggests that unregulated Toll-like receptors (TLRs) signaling promotes tumor survival 33 signals, thus favoring tumor progression. Here, the mechanism underlying TLR4 overexpression in papillary 34 thyroid carcinomas (PTCs) mainly harboring the BRAF V600E mutation was studied. TLR4 was overexpressed in 35 PTCs compared to non-neoplastic thyroid tissue. Moreover, paired clinical specimens of primary PTC and its 36 lymph node metastasis showed a significant upregulation of
... t upregulation of TLR4 levels in the metastatic tissues. In 37 agreement, conditional BRAF V600E expression in normal rat thyroid cells and mouse thyroid tissue 38 upregulated TLR4 expression levels. Furthermore, functional TLR4 expression was demonstrated in PTC 39 cells by increased NF-κB transcriptional activity in response to the exogenous TLR4-agonist 40 lipopolysaccharide (LPS). Of note, The Cancer Genome Atlas (TCGA) data analysis revealed that BRAF V600E -41 positive tumors with high TLR4 expression were associated with shorter disease-free survival. 42 Transcriptomic data analysis indicated a positive correlation between TLR4 expression levels and 43 MAPK/ERK signaling activation. Consistently, chemical blockade of MAPK/ERK signaling abrogated 44 BRAF V600E -induced TLR4 expression. A detailed study of the TLR4 promoter revealed a critical MAPK/ERK-45 sensitive Ets binding-site involved in BRAF V600E responsiveness. Subsequent investigation revealed that the 46 Ets-binding factor ETS1 is critical for BRAF V600E -induced MAPK/ERK signaling-dependent TLR4 gene 47 expression. Together, these data indicate that functional TLR4 overexpression in PTCs is a consequence of 48 thyroid tumor-oncogenic driver dysregulation of MAPK/ERK/ETS1 signaling. 49 IMPLICATIONS: Considering the participation of aberrant NF-κB signaling activation in the promotion of 50 thyroid tumor growth and the association of high TLR4 expression with more aggressive tumors, this study 51 suggests a pro-oncogenic potential of TLR4 downstream signaling in thyroid tumorigenesis. 52 KEYWORDS: Papillary thyroid carcinoma, BRAF V600E , Toll-like receptor 4, MAPK/ERK signaling pathway, ETS-53 domain transcription factor family. 54 on March 11, 2018.