PAX8-PPARgamma1 fusion oncogene in human thyroid carcinoma
Department of Pathology, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA. Science
(Impact Factor: 33.61).
Chromosomal translocations that encode fusion oncoproteins have been observed consistently in leukemias/lymphomas and sarcomas but not in carcinomas, the most common human cancers. Here, we report that t(2;3)(q13;p25), a translocation identified in a subset of human thyroid follicular carcinomas, results in fusion of the DNA binding domains of the thyroid transcription factor PAX8 to domains A to F of the peroxisome proliferator-activated receptor (PPAR) gamma1. PAX8-PPARgamma1 mRNA and protein were detected in 5 of 8 thyroid follicular carcinomas but not in 20 follicular adenomas, 10 papillary carcinomas, or 10 multinodular hyperplasias. PAX8-PPARgamma1 inhibited thiazolidinedione-induced transactivation by PPARgamma1 in a dominant negative manner. The experiments demonstrate an oncogenic role for PPARgamma and suggest that PAX8-PPARgamma1 may be useful in the diagnosis and treatment of thyroid carcinoma.
Available from: Jaegil Kim
- "Cell 159, 676–690, October 23, 2014 ª2014 The Authors 679 We identified PAX8/PPARG fusions in 4/484 (0.8%) tumors. Originally found in follicular carcinomas (Kroll et al., 2000), PAX8/PPARG translocations have been reported with low frequency in PTC, especially FV. ETV6/NTRK3 and RBPMS/ NTRK3 fusions were uncovered in 6/484 (1.2%) tumors. "
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ABSTRACT: Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer. Here, we describe the genomic landscape of 496 PTCs. We observed a low frequency of somatic alterations (relative to other carcinomas) and extended the set of known PTC driver alterations to include EIF1AX, PPM1D, and CHEK2 and diverse gene fusions. These discoveries reduced the fraction of PTC cases with unknown oncogenic driver from 25% to 3.5%. Combined analyses of genomic variants, gene expression, and methylation demonstrated that different driver groups lead to different pathologies with distinct signaling and differentiation characteristics. Similarly, we identified distinct molecular subgroups of BRAF-mutant tumors, and multidimensional analyses highlighted a potential involvement of oncomiRs in less-differentiated subgroups. Our results propose a reclassification of thyroid cancers into molecular subtypes that better reflect their underlying signaling and differentiation properties, which has the potential to improve their pathological classification and better inform the management of the disease.
Available from: Sherven Sharma
- "In adults it is expressed in thyroid follicular cells and is indispensable for the differentiation of thyroid cells . In follicular thyroid carcinoma, PAX8 undergoes gene rearrangement as a result of (2;3) (q13;p25) chromosomal translocation with peroxisome proliferator-activated receptor- γ(PPARγ). Significant expression of PAX8 was found in most carcinomas of thyroid, ovary and placenta [7-10]. "
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ABSTRACT: Non-small cell lung cancers (NSCLC) are highly heterogeneous at the molecular level and comprise 75% of all lung tumors. We have previously shown that the receptor tyrosine kinase (RTK) MET frequently suffers gain-of-function mutations that significantly promote lung tumorigenesis. Subsequent studies from our lab also revealed that PAX5 transcription factor is preferentially expressed in small cell lung cancer (SCLC) and promotes MET transcription. PAX8, however, is also expressed in NSCLC cell lines. We therefore investigated the role of PAX8 in NSCLC.
Using IHC analysis, PAX8 protein expression was determined in archival NSCLC tumor tissues (n = 254). In order to study the effects of PAX8 knockdown on NSCLC cellular functions such as apoptosis and motility, siRNA against PAX8 was used. Confocal fluorescence microscopy was used to monitor the localization of MET, RON and PAX8. The combinatorial effect of PAX8 knockdown and MET inhibition using SU11274 was investigated in NSCLC cell viability assay.
Relative levels of PAX8 protein were elevated (>= + 2 on a scale of 0-3) in adenocarcinoma (58/94), large cell carcinoma (50/85), squamous cell carcinoma (28/47), and metastatic NSCLC (17/28; lymph node). Utilizing early progenitors isolated from NSCLC cell lines and fresh tumor tissues, we observed robust overexpression of PAX8, MET, and RON. PAX8 knockdown A549 cells revealed abrogated PAX8 expression with a concomitant loss in MET and the related RON kinase expression. A dramatic colocalization between the active form of MET (also RON) and PAX8 upon challenging A549 cells with HGF was visualized. A similar colocalization of MET and EGL5 (PAX8 ortholog) proteins was found in embryos of C. elegans. Most importantly, knockdown of PAX8 in A549 cells resulted in enhanced apoptosis (~ 6 fold) and decreased cell motility (~45%), thereby making PAX8 a potential therapeutic target. However, the combinatorial approach of PAX8 knockdown and treatment with MET inhibitor, SU11274, had marginal additive effect on loss of NSCLC cell viability.
PAX8 provides signals for growth and motility of NSCLC cells and is necessary for MET and RON expression. Further investigations are necessary to investigate the therapeutic potential of PA8 in NSCLC.
Available from: Noelyn Anne Hung
- "In cancer, the over-expression of the PAX genes is often attributed to chromosomal rearrangements that result in fusion proteins [7,10,34,35]. In thyroid adenocarcinomas the PAX8/PPAR-γ (peroxisome proliferator-activator receptor gamma 1) fusion protein confers many oncogenic properties, including increased proliferation, decreased apoptosis and the inhibition of wild-type PPAR-γ [7,36-38]. "
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ABSTRACT: The molecular basis to overcome therapeutic resistance to treat glioblastoma remains unclear. The anti-apoptotic b cell lymphoma 2 (BCL2) gene is associated with treatment resistance, and is transactivated by the paired box transcription factor 8 (PAX8). In earlier studies, we demonstrated that increased PAX8 expression in glioma cell lines was associated with the expression of telomerase. In this current study, we more extensively explored a role for PAX8 in gliomagenesis METHODS: PAX8 expression was measured in 156 gliomas including telomerase-negative tumours, those with the alternative lengthening of telomeres (ALT) mechanism or with a non-defined telomere maintenance mechanism (NDTMM), using immunohistochemistry and quantitative PCR. We also tested the affect of PAX8 knockdown using siRNA in cell lines on cell survival and BCL2 expression RESULTS: Seventy-two percent of glioblastomas were PAX8-positive (80% telomerase, 73% NDTMM, and 44% ALT). The majority of the low-grade gliomas and normal brain cells were PAX8-negative. The suppression of PAX8 was associated with a reduction in both cell growth and BCL2, suggesting that a reduction in PAX8 expression would sensitise tumours to cell death.
PAX8 is increased in the majority of glioblastomas and promoted cell survival. Because PAX8 is absent in normal brain tissue, it may be a promising therapeutic target pathway for treating aggressive gliomas.
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