A Novel Molecular Pathway Involving GPR10, REST, and PRICKLE1 in the Pathogenesis of Uterine Leiomyoma

Abstract

Uterine Leiomyoma (UL), also known as Uterine Fibroids, are benign, hormone-sensitive tumors arising in the smooth muscle tissue layer of the uterus, the myometrium. UL are the most common female reproductive tract tumors, with lifetime occurrence in up to 77% of all women. A third of women with UL require treatment for clinically significant symptoms of menorrhagia, severe pain, anemia and fertility complications, resulting in over 200,000 hysterectomies and up to $34.4 billion in medical costs in the United States each year. Despite the prevalence of UL, currently no treatment for UL is long-term, cost effective and leaves fertility intact. There is a pressing need to develop better pharmacotherapies for the treatment of UL. Remarkably, very little is known about the molecular pathogenesis of UL. Environmental estrogen exposure is one of the most recognized risk factors associated with the development of UL tumors. At the cellular level, extensive evidence has linked the cell proliferation, survival and growth of UL tumors to the over-activation of the PI3K/AKT-mTOR pathway. This work establishes, for the first time, a comprehensive molecular pathway starting from known environmental estrogen risk factors leading to activation of the most crucial cell proliferation pathway in UL. We identified the most overexpressed G-protein coupled receptor in UL as the neuronspecific GPR10 (PRLHR), which activates the PI3K/AKT-mTOR pathway in UL cells upon stimulation by its ligand, PrRP (Prolactin-Releasing Peptide). Epigenetic silencing of GPR10 in non-neuronal cells is accomplished by the tumor-suppressor REST (Repressor Element Silencing Transcription factor), which we found to be drastically down-regulated at the protein level in UL tissue. In addition to GPR10, many of the most dysregulated genes in UL tissue are direct targets iv of REST, implicating the central role of the loss of REST in the pathogenesis of UL. In our investigations on the degradation of REST in UL, we found significant under-expression of PRICKLE1, the protein required for REST localization to the nucleus. We have found that PRICKLE1 expression in the uterine myometrium is regulated by estrogen through Estrogen Receptor-α and that the loss of PRICKLE1 leads to the destabilization and degradation of REST protein in UL. We found overexpression of the polycomb repressor complex protein EZH2 (Enhancer of Zeste Homolog 2) participates in repression of PRICKLE1 in UL. Furthermore, we provide two important preclinical mouse models, which are among the first in the UL field that recapitulate genes dysregulated in human UL. We show that mice expressing hGPR10 in the uterus, and a conditional knockout of REST in the reproductive tract, show UL phenotype. This work establishes a novel molecular pathway in UL pathogenesis linking upstream estrogen signaling to downstream PI3K/AKT-mTOR pathway activation and provides potential drug targets and preclinical mouse models for improved treatment of UL.