Fig. 4.

Progesterone is necessary for the CG-induced Notch1 induction in baboon endometrial stromal cells. A and B, Recapitulating the intrauterine endocrine milieu of early pregnancy with CG, increased Notch1 in the endometrial stroma. In baboons cotreated with onapristone, a pure PR antagonist (anti-PR), the stromal Notch1 is absent. Magnification, ×20. C and D, The inhibition of Notch1 in the presence of anti-PR is independent of PR status, as demonstrated by immunohistochemistry for PR in the endometrium, under both treatment paradigms. Magnification, ×20x. E, A dose-response experiment demonstrated that treatment of HuF with anti-PR (5 μm) abrogated the CG- plus hormone (H)-induced increase in Notch1. F, HuF cells from three separate isolations (P1–P3) demonstrated an increase in both the FL and TM forms of Notch1 with CG plus progesterone (P). However, the hormone-regulated increase in Notch1-TM was inhibited when cells were pretreated with anti-PR (5 μm) for 24 h before CG+H challenge. Furthermore, this was independent of the PR status of the cells. G, Immunoprecipitation (IP) with a PR antibody, followed by Western blot for Notch1, demonstrated that PR and Notch1 interact in a complex in the presence of progesterone, and this complex is not affected by anti-PR. PI, Preimmune.