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To examine the sex steroid-dependent growth mechanisms of the human endometrium, the expression of steroid receptor coactivators [steroid receptor coactivator-1 (SRC-1) and p300/CREB-binding protein (p300/CBP)] and corepressors (nuclear receptor corepressor and silencing mediator for retinoid and thyroid hormone receptors) was examined by immunohistochemistry, using 50 samples of normal endometria, and was compared with that of estrogen receptors (ER), progesterone receptors (PR), and proliferation marker Ki-67. In addition, actual binding of the coactivators to ER or PR was analyzed by immunoprecipitation. The expression of SRC-1 was diffusely observed in glandular and stromal cells in the proliferative phase and drastically decreased in the secretory phase. Such change in the expression pattern of SRC-1 resembled that of ER, PR, and Ki-67. On the other hand, p300/CBP expression was relatively constant throughout the menstrual cycle, with slight predominance in the proliferative phase. The expression of corepressors nuclear receptor corepressor and silencing mediator for retinoid and thyroid hormone receptors was focal in the endometrium. Immunoprecipitation, using tissue samples of both proliferative and secretory phases, revealed the complex formation between the coactivators and receptors. Binding of SRC-1 to ER was observed in the proliferative (but not in the secretory) endometrium. In contrast, binding p300/CBP to ER was noted in the endometria of both phases. Complex formation between p300/CBP and PR was noted in the secretory endometrium, whereas that between SRC-1 and PR was not apparent. Accordingly, we showed the expression pattern of steroid receptor coactivators and corepressors in the normal endometrium. Cyclic change in the expression of SRC-1 during the menstrual cycle might be important in the estrogen-action for the glandular and stromal cells.

Although progestins have been used for the treatment of endometrial neoplasias, the mechanisms of progestin-induced growth suppression remain undetermined.Immunostaining for steroid receptor coactivators (SRC-1, p300/CBP), corepressors (NCoR, SMRT) and Ki-67 in 15 neoplastic endometria before and after the treatment with medroxyprogesterone acetate (MPA) was performed. The effect of progestin on cell proliferation and cofactors expression were examined using T47D cells.Of the 15 cases, 10 showed good histological responses to MPA (Responder) and 5 poor responses (Non-responder). In Responders, MPA treatment resulted in reduced expression of Ki-67 by 78% (p=0.0076) along with increased NCoR expression by 158 % (p=0.0077). Progestin treatment for T47D cells resulted in up-regulation of NCoR mRNA and protein with the suppression of cell proliferation. Immunoprecipitation revealed that NCoR was bound to estrogen receptor alpha, but not to progesterone receptor in T47D cells.The up-regulation of NCoR by progestins is associated with the suppression of estrogen-induced growth of neoplastic cells.

To examine estrogen-induced growth mechanisms of endometrial carcinoma, we investigated the estrogen-induced activation of the mitogen-activated protein kinase (MAPK) pathway and cell cycle regulators. Estradiol (E2) treatment at concentrations of 10−8 M and 10−6 M to estrogen receptor (ER)-positive endometrial carcinoma Ishikawa cells for 24 h resulted in increased cell proliferation by 20% and 28% respectively. The E2-induced proliferation was associated with the activation of extracellular signal-regulated kinase (MAPK)3/1 and up-regulation of cyclin D1 and E, which were suppressed by the addition of an MAP2K inhibitor (U0126) or an ER antagonist (ICI 182 780). Then, our screening for estrogen-inducible growth factors identified that IGF1 was up-regulated remarkably by E2. Immunoprecipitation using conditioned medium of Ishikawa cells after E2 treatment confirmed the E2-induced secretion of IGF1 protein. Treatment with recombinant IGF1 stimulated cell proliferation in a dose-dependent fashion, in association with MAPK3/1 phosphorylation and up-regulation of cyclin D1 and E. These IGF1-induced responses were suppressed by treatment with MAP2K inhibitor or anti-IGF1 receptor antibody. Immunohistochemical staining confirmed the expression of activated MAPK3/1 in normal proliferative phase endometria and endometrial carcinomas, indicating the involvement of this pathway in actively proliferating endometrial tissues in vivo. These findings suggest that E2-induced proliferation of endometrial carcinoma cells is mediated by the MAPK3/1 pathway via autocrine stimulation of IGF1.

beta-catenin has recently been reported to act as a cell growth promoter through cyclin D1 transcription. However, the correlation between beta-catenin and cyclin D1 expressions is not fully understood in endometrial tissues.Immunohistochemical expression of beta-catenin was examined in normal endometria (32 cases) and endometrial carcinomas (82 cases), and its expression was compared with that of cyclins (D1, E, A, B1).Sporadic nuclear staining of beta-catenin and cyclins was observed from proliferative phase of early secretory phase endometria, however, spacial correlations between beta-catenin and cyclins were not evident. In endometrial carcinomas, positivity for nuclear beta-catenin and cyclins increased compared to the normal endometria. Topologically, the cyclin D1-positive cells were frequently found in nuclear beta-catenin-positive cells. In addition, Spearman's rank correlation analysis revealed that the nuclear expression of beta-catenin correlated positively with that of cyclin D1 (p0.0001).The beta-catenin-cyclin D1 pathway might be involved in the growth of endometrial carcinomas.

BACKGROUND To examine the steroid hormone dependent growth mechanism of human endometrial hyperplasia and carcinoma, expression levels of steroid receptor cofactors, such as coactivators (steroid receptor coactivator 1 [SRC-1] and p300/cyclic AMP-response element-binding protein (p300/CBP]) and corepressors (nuclear receptor corepressor [NCoR] and silencing mediator for retinoid and thyroid-hormone receptors [SMRT]), were investigated. METHODS The expression levels of cofactors were examined immunohistochemically using 20 samples of normal endometria, 36 samples of hyperplastic endometria, and 58 of malignant endometria and were compared with the expression levels of estrogen receptor (ER), progesterone receptor (PR), and a proliferation marker, Ki-67. RESULTS In samples of normal endometria, the expression of coactivators was observed diffusely in glandular cells in the proliferative phase, with a mean positivity index (PI) of 81.8 for SRC-1 and 91.3 for p300/CBP, whereas expression levels decreased in endometrial hyperplasia (PI: SRC-1, 58.9; p300/CBP, 83.8) and endometrial carcinoma (PI: SRC-1, 45.0; p300/CBP, 55.4). In endometrial hyperplasia, there was a significant correlation between the expression of ER and SRC-1 or p300/CBP. In contrast, there were no significant statistical or topologic correlations between the expression of coactivators and the expression of ER/PR in endometrial carcinoma. The expression of corepressors generally was limited, except for elevated expression of NCoR in endometrial hyperplasia (PI, 23.8). CONCLUSIONS The current study showed that expression levels of the steroid receptor coactivators SRC-1 and p300/CBP were reduced in endometrial carcinoma compared with normal and hyperplastic endometrium. In addition, topologic coexpression of both coactivators and ER/PR was lost in endometrial carcinoma. Accordingly, limited response to sex steroids in patients with endometrial carcinoma may be ascribed to the dissociation of cofactors and ER/PR. Cancer 2003. © 2003 American Cancer Society.