RAD51 paralog B (RAD51B), the preferential translocation partner of HMGA2, was up-regulated in MED12 mutant lesions, suggesting a role for this gene in the genesis of leiomyomas.
The results confirm the occurrence of fibroid-type MED12 mutations in malignant uterine smooth muscle tumors thus suggesting a rare but existing leiomyoma-LMS sequence.
The DEGs in the MED12 mutation and wild-type leiomyoma samples, and common DEGs were defined as group A, B and C. Gene Ontology (GO) and pathway enrichment analyses were performed using the Database for Annotation, Visualization and Integrated Discovery online tool.
However, G>A transitions of nucleotides c.130 or c.131 correlate with a significantly larger size of the fibroids compared to other MED12 mutations thus explaining the high prevalence of the former mutations among clinically detectable fibroids.
Our results confirm the findings of similar recent studies and further show that pelvic and retroperitoneal leiomyomas harbor an increased frequency of MED12 mutations (34%) as compared with other extrauterine sites (0%; P = 0.0006), and that histologically unremarkable adjacent myometrium can harbor similar MED12 mutations.
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.
Interestingly all classical leiomyomas exhibit MED12 protein expression while 40% of atypical leiomyomas, 50% of STUMP and 80% of leiomyosarcomas (among them the two mutated ones) do not express MED12.
MED12 mutations were the most common alterations in conventional and mitotically active leiomyomas and leiomyosarcomas, while leiomyomas with bizarre nuclei were most often FH deficient and cellular tumors showed frequent HMGA2 overexpression.
Immunoblotting studies demonstrated MED12 protein expression in 100% of leiomyomas (13) and leiomyosarcomas (20), irrespective of MED12 exon 2 mutation status or histological grade.
Herein, we determined the frequency of MED12 gene exon 2 somatic mutations in 143 fibroid tumors from a total of 135 women from the Southern United States and in 50 samples of the adjacent myometrium using PCR amplification and Sanger sequencing.
MED12-negative leiomyomas contain copy number alterations involving the Mediator complex subunits such as MED8, MED18, CDK8, and long intergenic nonprotein coding RNA340 (CASC15), which may affect the Mediator architecture and/or its transcriptional activity.