Proline-Rich Acidic Protein 1 (PRAP1) is a Target of ARID1A and PGR in the Murine Uterus

ARID1A and PGR plays an important role in embryo implantation and decidualization during early pregnancy. Uterine specific Arid1a knockout ($Pgr^{cre/+}Arid1a^{f/f}$) mice exhibit in non-receptive endometrium at day 3.5 of gestation (GD 3.5). In previous studies, using transcriptomic analysis in the uterus of $Pgr^{cre/+}Arid1a^{f/f}$ mice, we identified proline-rich acidic protein 1 (PRAP1) as one of the down-regulated genes by ARID1A in the uterus. In the present study, we performed RT-qPCR and immunohistochemistry analysis to investigate the regulation of PRAP1 by ARID1A and determine expression patterns of PRAP1 in the uterus during early pregnancy. During early pregnancy, PRAP1 expression was strong at day 0.5 of gestation (GD 0.5) and then decreased at GD 3.5 in the epithelium and stroma. After implantation, PRAP1 expression was remarkably reduced in the uterus. However, the expression of PRAP1 at GD 3.5 was remarkably increased in the $Pgr^{cre/+}Arid1a^{f/f}$ mice. To determine the ovarian steroid hormone regulation of PRAP1, we examined the expression of PRAP1 in ovariectomized control, $Pgr^{cre/+}Arid1a^{f/f}$, and progesterone receptor knock-out (PRKO) mice treated with progesterone. While PRAP1 proteins were strongly expressed in the luminal and glandular epithelium of control mice treated with vehicle, progesterone treatment suppressed the expression of PRAP1. However, PRAP1 was not suppressed in both the $Pgr^{cre/+}Arid1a^{f/f}$ and PRKO mice compared to controls. Our results identified PRAP1 as a novel target of ARID1A and PGR in the murine uterus.