Expression of PTEN in human endometrium throughout the menstrual cycle and during early pregnancy and its regulation by progesterone

Objective: PTEN/MMAC (phosphatase and tensin homologue/mutated in multiple advanced cancers) is a novel tumor suppressor protein. PTEN regulates cell growth, invasion and apoptosis. When PTEN is phosphorylated, its degradation and activity are inhibited. Homozygosity for PTEN gene mutation causes defective placentation and developmental delay, and results in embryonal lethality on day E9.5. The heterozygosity for PTEN gene mutation induces endometrial tumors suggesting a fundamental role for PTEN in endometrial proliferation and early pregnancy in mice. We hypothesized that PTEN has a temporal and spatial expression model throughout the menstrual cycle and during early pregnancy, and progesterone regulates PTEN by affecting either its expression and/or phosphorylation. Design: PTEN expression was studied in normal human endometrial and decidual tissues. Its regulation by progesterone was investigated in cultured human endometrial stromal cells. Materials/Methods: Paraffin and frozen section were obtained from clinically normal endometrium (n 18) and from clinically normal decidua (n 10) of early pregnancies voluntarily terminated by dilation and curettage. To investigate the effect of progesterone on PTEN level and on its phosphorylation, normal and phosphorylated (phospho-PTEN) forms of PTEN were evaluated using Western blot analysis in endometrial stromal cell cultures. Cells were treated with progesterone (10 9 M) for 5 to 30 min to evaluate the short-term effect and for 6–24 h to evaluate the long-term effect on PTEN levels. GAPDH immunoblot analysis was carried out to verify equal loading of proteins. Statistical analysis was done using Student s t-test. Results: Immunohistochemical results revealed that stromal cells had a stronger immunoreactivity for PTEN than glandular cells throughout the menstrual cycle. The immunoreactivity for PTEN was stronger during early proliferative and late secretory phases in both stromal and glandular cells compared to other cycle phases. On the other hand, among the groups, the strongest immunoreactivity was observed in both glandular and decidual cells during early pregnancy with a gradual increase as pregnancy progressed (P 0.05). Both PTEN and phospho-PTEN protein expression were detected in endometrial stromal cells in vitro. Short-term treatment of cells with progesterone decreased both PTEN and phospho-PTEN levels when compared to vehicle (control). PTEN and phospho-PTEN levels were found 23 % and 19 % lower, respectively, in endometrial stromal cells exposed to progesterone for 30 min as compared to vehicle. Interestingly, long-term treatment of cells with progesterone for 6 to 24 h upregulated PTEN and phospho-PTEN levels up to 75 % and 30 %, respectively. Conclusions: Our results showed that PTEN has a specific temporal and spatial expression model in endometrium and decidua throughout the menstrual cycle and early pregnancy, and is likely to be regulated by ovarian hormones. Progesterone-mediated regulation of PTEN supports this finding. Furthermore, progesterone is likely to regulate the PTEN pool by decreasing its phosphorylation in shortterm and increasing protein level in long-term. We conclude that regulation of PTEN may be one of the pathways that progesterone is acting to affect endometrial cell proliferation and/or apoptosis. Supported by: None provided.