Endometrial stromal cells in culture: an attempt to understand the genesis and biologic activity of uterine sarcomas

Diethylstilbestrol-induced immortalization of human endometrial cells: alterations in p53 and estrogen receptor

Carcinogenesis is a process requiring multiple steps. Immortalization is one step in this process and may be rate limiting. To further our understanding of estrogen-induced carcinogenesis, we evaluated diethylstilbestrol (DES)-induced immortalization of human endometrial stromal cells. This was achieved by assessing at the restrictive temperature the colony-forming efficiency of cells that were conditionally immortalized with a temperature-sensitive simian virus 40 large T antigen. Treatment with DES for 1 wk did not increase the immortalization frequency; however, cultures that were treated for 20 wk had a twofold increase in immortalization frequency, and continued treatment for a total of 44 wk produced a threefold increase in immortalization frequency that was dose dependent. DES-treated restrictive temperature variants (RTVs) but not spontaneous RTVs lost the temperature-sensitive phenotype. DES-RTVs also had a shorter doubling time than spontaneous RTVs did. p53 expression was increased in DES-RTVs, and its localization within the cell was altered. Conversely, expression of the estrogen receptor was decreased in DES-immortalized cells. These changes in gene expression often occur in estrogen-related malignancies, and our results are consistent with a causal role for estrogens in these p53 and the estrogen receptor alterations. Immortalization of human cells may be analogous to initiation of rodent cells, and our results suggest that estrogen-induced alterations in p53 or other genes that regulate life span could contribute to estrogen-induced initiation.

Estrogen-induced anchorage-independence in human endometrial stromal cells

Estrogens are important etiologic agents for most gynecologic malignancies, and chronic exposure to estrogen that is unopposed by progestins conveys the greatest risk. Treatments with estrogen facilitate the process of malignant transformation in rodents, but relatively few studies of estrogen-induced carcinogenesis have been performed using human cells. Most malignancies in estrogen-responsive tissues arise from epithelial cells, but an increasing body of evidence emphasizes the role of stromal cells as mediators of the effects of estrogens on epithelial cells. Our studies were designed to assess estrogens as carcinogens for human endometrial stromal cells and to provide a basis for studies of the role of stroma in estrogen-induced carcinogenesis in humans. Acute treatments with the estrogens diethylstilbestrol (DES), 17 beta-estradiol (E2) and beta-dienestrol enhance anchorage-independent proliferation (AIP) of SV40-immortalized human endometrial stromal cells in the rank order of DES > E2 > beta-dienestrol. The anti-estrogenic compound tamoxifen inhibits DES-induced AIP. The magnitude of DES-induced AIP increases with prolonged duration of treatment. After 11 months of chronic treatment with 0.1 nM DES, AIP was 20-fold higher than in vehicle-treated control cultures. Expression of the estrogen receptor was altered by treatments with DES in parallel with increased capacity for AIP. These conditionally immortal human endometrial stromal cells appear to be a good model for estrogen-induced transformation of human cells.