A mediator complex subunit 12 gain-of-function mutation induces partial leiomyoma cell properties in human uterine smooth muscle cells

Objective: To clarify whether a mediator complex subunit 12 (MED12) gain-of-function mutation induces leiomyoma cell properties in human uterine smooth muscle cells (USMCs). Design: Experimental study. Setting: Academic research laboratory. Patient(s): Women undergoing hysterectomy for leiomyoma. Intervention(s): CRISPR/Cas9-mediated genome editing to introduce an MED12 gain-of-function mutation (G44D) into human USMCs. Main Outcome Measure(s): Cell proliferation, collagen production, and in vivo tumorigenicity of USMCs with vs. without the MED12 mutation. Result(s): Uterine smooth muscle cells isolated from the uterine myometrium of a 44-year-old patient were subjected to lentiviral vector-mediated gene transduction of the fluorescent protein Venus, followed by long-term passage. Uterine smooth muscle cells with a normal female karyotype, high cell proliferative activity, and Venus expression, but without stem/progenitor cell populations, were obtained and designated as USMC44. Using CRISPR/Cas9-mediated genome editing, mtUSMC44 (MED12, 131G>A, p.G44D) and mock USMC44 without MED12 mutation (wtUSMC44) were established from USMC44. wtUSMC44 and mtUSMC44 showed similar cell proliferation activity, even in the presence of estradiol and progesterone (EP) together with transforming growth factor-beta 3 (TGFB3). In addition, wtUSMC44 and mtUSMC44 generated similar tiny smooth muscle-like tissue constructs when xenotransplanted beneath the kidney capsule in immunodeficient mice treated with EP alone or TGFB3. In contrast, mtUSMC44 produced more collagen type I than wtUSMC in vitro, and this production was likely enhanced by EP and TGFB3. Conclusion(s): The results suggest that the MED12 gain-of-function mutation is involved in collagen production. Although approximately 70% of leiomyomas have MED12 mutations, additional factors and/or events other than MED12 and/or myometrial stem/progenitor cells may be required for fully inducing leiomyoma cell properties, including transformation, in USMCs.