MED12 somatic mutation promotes human uterine leiomyoma’s growth by trigging canonical Wnt4/β-catenin and TGF-β signaling through the EMT pathway

• Uterine leiomyoma (UL) is a monoclonal benign smooth muscle tumor with unknown pathophysiology. • Somatic mutation (131 G > A) on exon-2 of the MED12 gene in UL showed pathogenic and lethal impact. • Mutation in exon-2 of MED-12 gene up-regulates the expression of conserved MED-12 protein in UL cells. • Mutation (131 G > A) aggressively activates Wnt4/β-catenin and TGF-β signalling pathways which promote ECM deposition in UL. Somatic mutation in mediator complex subunit 12 (MED12) plays a significant role in the transformation of normal myometrium to uterine leiomyomas (UFs); however, the molecular mechanism of UF caused by genetic aberrations in the MED12 gene remains unclear. We established a patient-derived primary culture of tissue sample and confirmed MED12 mutations in UF tissue and primary culture by Sanger sequencing and RT-PCR. Further, to investigate the functional relationship between MED12-wild and MED12-mut, Wnt4/β-catenin signaling with TGF-β pathways was investigated. We found a single nucleotide substitution in exon-2 of MED12 (c.131 G > A), consequently leading to a change in amino acid from Glycine to Aspartate, which has a pathogenic and lethal impact. We have shown that this somatic mutation (131 G > A) aggressively activates Wnt4/β-catenin and TGF-β signaling to promote growth, proliferation, and ECM deposition by targeting the EMT pathway in MED12-Mut compared to MED12-WT UL cells. Analysis of Vimentin, MMP-2/9, and α-SMA protein expression levels in the same set of ULs revealed significantly higher expression in MED12-mut compared to MED12-wild type of tissue. We conclude that mutation in the MED12 gene in ULs triggers two mutually exclusive pathways, one with over-expression of ECM protein, and another with epithelial-mesenchymal transition (EMT) pathway in the genesis of ULs.