Inhibition of tumor cell proliferation in human uterine leiomyomas by vitamin D via Wnt/β-catenin pathway.

Objective: To assess the effect of vitamin D (VitD) on human uterine leiomyomas through Wnt/β-catenin pathway inhibition, apoptosis induction, and cell growth arrest.

Design: A prospective study comparing leiomyoma vs. myometrium tissues. Paired design study comparing human uterine leiomyoma primary (HULP) cells treated with or without VitD.

Setting: University hospital.

Patient(s): Human uterine leiomyoma and myometrium were collected from women (aged 35-52 years) without hormonal treatment.

Intervention(s): Samples were collected from women undergoing surgery due to symptomatic uterine leiomyoma pathology.

Main Outcome Measure(s): Uterine leiomyoma and myometrium tissues were analyzed by western blot (WB) to determine proliferation, Wnt/β-catenin, and apoptosis pathways. HULP cells were used to study VitD effect in cell proliferation (WB), cell cycle (flow cytometry), Wnt/β-catenin and apoptosis genes (polymerase chain reaction arrays), Wnt-related proteins (protein array), and apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling [TUNEL] assay).

Results: Human leiomyoma tissues compared with matched myometrium showed higher proliferation (fold change = 8.16; P=.0006) and altered Wnt/β-catenin pathway (fold change = 5.5; P<.0001), whereas no differences in apoptosis were observed. VitD induced cell growth arrest and decreased proliferation in HULP cells (fold change = 0.74; P=.007). Moreover, VitD decreased Wnt-pathway expression in HULP cells at gene (activity score = -0.775; P<.001) and protein levels. However, VitD did not induce apoptosis expression.

Conclusion: Increased proliferation and Wnt/β-catenin pathway deregulation play a role in the development and growth of leiomyomas, whereas apoptosis appears not to contribute. VitD exerts an antiproliferative action on HULP cells through cell growth arrest and Wnt/β-catenin pathway inhibition, but not through apoptosis regulation, suggesting VitD as an effective therapy to stabilize leiomyoma size and prevent its growth.