Oncotarget

Priority Research Papers:

Genomic binding and regulation of gene expression by the thyroid carcinoma-associated PAX8-PPARG fusion protein

Yanxiao Zhang, Jingcheng Yu, Chee Lee, Bin Xu, Maureen A. Sartor and Ronald J. Koenig _

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Oncotarget. 2015; 6:40418-40432. https://doi.org/10.18632/oncotarget.6340

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Abstract

Yanxiao Zhang1,*, Jingcheng Yu2,*, Chee Lee1,*, Bin Xu2, Maureen A. Sartor1 and Ronald J. Koenig2

1 Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, USA

2 Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA

* These authors have contributed equally to this work

Correspondence to:

Ronald J. Koenig, email:

Keywords: peroxisome proliferator-activated receptor gamma, follicular thyroid cancer, pioglitazone, differentiation, gene fusion

Received: September 16, 2015 Accepted: November 11, 2015 Published: November 16, 2015

Abstract

A chromosomal translocation results in production of an oncogenic PAX8-PPARG fusion protein (PPFP) in thyroid carcinomas. PAX8 is a thyroid transcription factor, and PPARG is a transcription factor that plays important roles in adipocytes and macrophages. PPFP retains the DNA binding domains of both proteins; however, the genomic binding sites of PPFP have not been identified, and only limited data exist to characterize gene expression in PPFP thyroid carcinomas. Therefore, the oncogenic function of PPFP is poorly understood. We expressed PPFP in PCCL3 rat thyroid cells and used ChIP-seq to identify PPFP genomic binding sites (PPFP peaks) and RNA-seq to characterize PPFP-dependent gene expression. PPFP peaks (~20,000) include known PAX8 and PPARG binding sites and are enriched with both motifs, indicating that both DNA binding domains are functional. PPFP binds to and regulates many genes involved in cancer-related processes. In PCCL3 thyroid cells, PPFP binds to adipocyte PPARG target genes in preference to macrophage PPARG target genes, consistent with the pro-adipogenic nature of PPFP and its ligand pioglitazone in thyroid cells. PPFP induces oxidative stress in thyroid cells, and pioglitazone increases susceptibility to further oxidative stress. Our data highlight the complexity of PPFP as a transcription factor and the numerous ways that it regulates thyroid oncogenesis.


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