Muscle Stem Cell Function Is Impaired in ß2-Adrenoceptor Knockout Mice.

Knockout (ko) mice for the ß2 adrenoceptor (Adrß2) have impaired skeletal muscle regeneration, suggesting that this receptor is important for muscle stem cell (satellite cell) function. Here, we investigated the role of Adrß2 in the function of satellite cells from ß2ko mice in the context of muscle regeneration, through in vivo and in vitro experiments. Immunohistochemical analysis showed a significant reduction in the number of self-renewed Pax7+ satellite cells, proliferating Pax7+/MyoD+ myogenic precursor cells, and regenerating eMHC+ myofibers in regenerating muscle of ß2ko mice at 30, 3, and 10 days post-injury, respectively. Quiescent satellite cells were isolated by fluorescence-activated cell sorting, and cell cycle entry was assessed by EdU incorporation. The results demonstrated a lower number of proliferating Pax7+/EdU+ satellite cells from ß2ko mice. There was an increase in the gene expression of the cell cycle inhibitor Cdkn1a and Notch pathway components and the activation of Notch signaling in proliferating myoblasts from ß2ko mice. There was a decrease in the number of myogenin-positive nuclei in myofibers maintained in differentiation media, and a lower fusion index in differentiating myoblasts from ß2ko mice. Furthermore, the gene expression of Wnt/ß-catenin signaling components, the expression of nuclear ß-catenin and the activation of Wnt/ß-catenin signaling decreased in differentiating myoblasts from ß2ko mice. These results indicate that Adrß2 plays a crucial role in satellite cell self-renewal, as well as in myoblast proliferation and differentiation by regulating Notch and Wnt/ß-catenin signaling, respectively.

Functional Toll-like Receptor 4 Overexpression in Papillary Thyroid Cancer by MAPK/ERK-Induced ETS1 Transcriptional Activity.

Emerging evidence suggests that unregulated Toll-like receptor (TLR) signaling promotes tumor survival signals, thus favoring tumor progression. Here, the mechanism underlying TLR4 overexpression in papillary thyroid carcinomas (PTC) mainly harboring the BRAFV600E mutation was studied. TLR4 was overexpressed in PTC compared with nonneoplastic thyroid tissue. Moreover, paired clinical specimens of primary PTC and its lymph node metastasis showed a significant upregulation of TLR4 levels in the metastatic tissues. In agreement, conditional BRAFV600E expression in normal rat thyroid cells and mouse thyroid tissue upregulated TLR4 expression levels. Furthermore, functional TLR4 expression was demonstrated in PTC cells by increased NF-κB transcriptional activity in response to the exogenous TLR4-agonist lipopolysaccharide. Of note, The Cancer Genome Atlas data analysis revealed that BRAFV600E-positive tumors with high TLR4 expression were associated with shorter disease-free survival. Transcriptomic data analysis indicated a positive correlation between TLR4 expression levels and MAPK/ERK signaling activation. Consistently, chemical blockade of MAPK/ERK signaling abrogated BRAFV600E-induced TLR4 expression. A detailed study of the TLR4 promoter revealed a critical MAPK/ERK-sensitive Ets-binding site involved in BRAFV600E responsiveness. Subsequent investigation revealed that the Ets-binding factor ETS1 is critical for BRAFV600E-induced MAPK/ERK signaling-dependent TLR4 gene expression. Together, these data indicate that functional TLR4 overexpression in PTCs is a consequence of thyroid tumor-oncogenic driver dysregulation of MAPK/ERK/ETS1 signaling.Implications: Considering the participation of aberrant NF-κB signaling activation in the promotion of thyroid tumor growth and the association of high TLR4 expression with more aggressive tumors, this study suggests a prooncogenic potential of TLR4 downstream signaling in thyroid tumorigenesis. Mol Cancer Res; 16(5); 833-45. ©2018 AACR.

Functional characterization of the novel BRAF complex mutation, BRAF(V600delinsYM) , identified in papillary thyroid carcinoma.

An activating mutation in the BRAF gene is the most common genetic alteration in papillary thyroid carcinomas (PTCs). The mutation in PTCs is almost a c.1799T>A transversion, resulting in a p.V600E amino acid substitution (BRAF(V600E) ). Here, we report a novel complex BRAF mutation identified in 4/492 Japanese PTC cases (0.81%). The mutation was comprised of one nucleotide substitution at position 1798, followed by an in-frame insertion of three nucleotides, c.1798delinsTACA in Exon 15, resulting in p.V600delinsYM. In silico three-dimensional protein structure prediction implied altered kinase activity of this mutant. In vitro kinase assay and western blotting revealed that this mutation conferred high kinase activity on the BRAF protein, leading to constitutive activation of the MAPK signaling pathway. The mutation also showed high transforming ability in focus formation assay using NIH3T3 cells. The degree of all the functional characteristics was comparable to that of BRAF(V600E) , and treatment with a BRAF inhibitor Sorafenib was also equally effective in this mutant. These findings suggest that the novel BRAF mutation, BRAF(V600delinsYM) , is a gain-of-function mutation and plays an important role in PTC development.