Uterine function in the mouse requires speckle-type poz protein

Speckle-type poz protein (SPOP) is an E3-ubiquitin ligase adaptor for turnover of a diverse number of proteins involved in key cellular processes such as chromatin remodeling, transcriptional regulation, and cell signaling. Genomic analysis revealed that SPOP somatic mutations are found in a subset of endometrial cancers, suggesting that these mutations act as oncogenic drivers of this gynecologic malignancy. These studies also raise the question as to the role of wild-type SPOP in normal uterine function. To address this question, we generated a mouse model (Spop^d/d) in which SPOP is ablated in uterine cells that express the PGR. Fertility studies demonstrated that SPOP is required for embryo implantation and for endometrial decidualization. Molecular analysis revealed that expression levels of the PGR at the protein and transcript level are significantly reduced in the Spop^d/d uterus. While this result was unexpected, this finding explains in part the dysfunctional phenotype of the Spop^d/d uterus. Moderate increased levels of the ESR1, GATA2, and SRC2 were detected in the Spop^d/d uterus, suggesting that SPOP is required to maintain the proteome for normal uterine function. With age, the Spop^d/d endometrium exhibits large glandular cysts with foci of epithelial proliferation, further supporting a role for SPOP in maintaining a healthy uterus. Collectively, studies on the Spop^d/d mouse support an important role for SPOP in normal uterine function and suggest that this mouse model may prove useful to study the role of SPOP-loss-of-function mutations in the etiopathogenesis of endometrial cancer.