Integrated Epigenome, Exome, and Transcriptome Analyses Reveal Molecular Subtypes and Homeotic Transformation in Uterine Fibroids

Summary: Uterine fibroids are benign myometrial smooth muscle tumors of unknown etiology that, when symptomatic, are the most common indication for hysterectomy in the United States. Unsupervised clustering of results from DNA methylation analyses segregates normal myometrium from fibroids and further segregates the fibroids into subtypes characterized by MED12 mutation or activation of either HMGA2 or HMGA1 expression. Upregulation of HMGA2 expression does not always appear to be dependent on translocation but is associated with hypomethylation in the HMGA2 gene body. HOXA13 expression is upregulated in fibroids and correlates with expression of typical uterine fibroid genes. Significant overlap of differentially expressed genes is observed between cervical stroma and uterine fibroids compared with normal myometrium. These analyses show a possible role of DNA methylation in fibroid biology and suggest that homeotic transformation of myometrial cells to a more cervical stroma phenotype could be an important mechanism for etiology of the disease. : George et al. detect DNA hypomethylation in the HMGA2 gene body in uterine fibroids expressing high levels of HMGA2, regardless of translocation, suggesting an alternative mechanism of activation. They also observe HOXA13 overexpression in fibroids, evidence of pathogenic homeotic transformation of myometrial cells to a more cervical stroma phenotype. Keywords: Leiomyoma, clonal, epigenome, methylome, transcriptome, exome, mutational burden, CTCF, A/B compartments, homeobox