The use of a human endometrial carcinoma cell line (RL-95) for in vitro testing of chemotherapeutic agents

Up-regulation of DNA methyltransferase 3B expression in endometrial cancers

OBJECTIVE

To understand the role of epigenetic regulation in the pathogenesis of endometrial cancer, we have characterized DNA methyltransferase 3B (DNMT3B) gene expression in normal, Grade I and Grade III endometrioid cancers, and examined DNMT3B promoter activities in endometrial cancer cell lines.

METHODS

DNMT3B expression was measured in normal, Grade I, and Grade III endometrioid cancer samples. Real-time PCR and Western blot analysis were performed to compare DNMT3B mRNA and protein levels. DNMT3B levels were also compared among endometrial cell lines including those for Ishikawa, KLE, AN3, RL-95, HEC-1A, and HEC-1B. DNMT3B promoter reporter plasmids were constructed. Promoter activities in well and poorly differentiated cell lines were compared by in vitro reporter gene transfection.

RESULTS

DNMT3B was significantly up-regulated in both Grade I and Grade III cancers as compared to normal controls. Western blot analysis confirmed the increased DNMT3B protein expression in cancer tissues. It was also found that the well-differentiated endometrial cell line, Ishikawa, expressed lower levels of DNMT3B than the poorly differentiated KLE cells, the expression patterns similar to those observed in tumor specimens.

CONCLUSION

The results suggest that DNMT3B overexpression may play a significant role in endometrial cancer development. In addition, the transfection experiments indicated that DNMT3B promoters are more active in the poorly differentiated endometrial cancer cell lines, suggesting that the in vitro assay provides a useful model for studying the DNMT3B transactivation mechanism related to tumor transformation.

The role of interleukin-1 in interactive senescence and age-related human endometrial cancer

The causes of the age-related increase in cancer rates are poorly understood. One cause could be age-related changes in the stromal/epithelial cell interactions that facilitate tumorigenesis. We tested the hypothesis that aging of human endometrial stromal fibroblasts (ESF) alters their influence over endometrial epithelial cells. ESF from adults were found to inhibit anchorage-independent proliferation, to restrain colony outgrowth, and to induce formation of normal tissue architecture by human endometrial cancer cells. As ESF age, these inhibitory influences on malignant-like behaviors by epithelial cells are altered, becoming stimulatory. Age-related change in interleukin-1alpha (IL-1alpha) expression is a molecular determinant of ESF/epithelial cell interactions. Levels of IL-1alpha and IL-1-induced mRNAs increase in ESF with age. Treatment with IL-1 accelerates age-related changes in mRNA abundance and loss of ESF restraint over malignancy-associated behaviors by epithelial cells. Transfection of ESF with the intracellular IL-1 receptor antagonist preserved the young phenotype with respect to interactions with epithelial cells and prevented age-associated increases in groalpha and IL-8 mRNA levels. Our results indicate that aging of ESF is accompanied by an interactive senescence that alters ESF signaling to cancer cells and could contribute to increased cancer rates by providing a microenvironment that is more conducive to tumorigenesis.

Age-related expression of PEDF/EPC-1 in human endometrial stromal fibroblasts: implications for interactive senescence

Aging is the major risk factor for many cancers, and age-related changes in the tissue microenvironment can facilitate tumor growth. This study uses human endometrial cells to begin to test the hypothesis that age-related changes in pigment epithelium-derived factor/early population doubling cDNA-1 (PEDF/EPC-1) levels create an environment that is more permissive to tumor growth. Endometrial stromal fibroblasts (ESF) are the predominant cell type in the human endometrium and exert regulatory control over the glandular epithelial cells, which are the source of most tumors. As ESF age in vitro, their ability to regulate appropriate growth and differentiation of epithelial cells declines. Endometrial epithelial cells in primary culture expressed relatively low levels of PEDF/EPC-1 mRNA. In contrast, early passage quiescent ESF from adult donors produce higher levels of the 1.5-kb PEDF/EPC-1 mRNA and 50-kDa secreted protein than epithelial cells. As ESF age in vitro the relative abundance of PEDF/EPC-1 mRNA declines, as does the level of PEDF/EPC-1 protein secreted into cell culture medium. Treatment with PEDF/EPC-1 protein had no effect on ESF proliferation but did inhibit anchorage-dependent and anchorage-independent proliferation of endometrial carcinoma cells in a dose- and time-dependent manner. These findings imply that an age-related loss of PEDF/EPC-1 expression by ESF could eliminate a negative regulator of cancer cell growth and, thereby, contribute to the age-related increase in cancer incidence.

Vitamin D receptor in endometrial carcinoma and the differentiation-inducing effect of 1,25-dihydroxyvitamin D3 on endometrial carcinoma cell lines

In view of the potential of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] as a cell-differentiation-inducing agent in endometrial cancer, the localization of the vitamin D receptor (VDR) was examined immunohistochemically in 21 endometrial adenocarcinoma specimens, and the effect of 1,25(OH)2D3 on cell growth, as well as the phenotypic changes for cell maturation after treatment with 1,25(OH)2D3, was investigated in 2 endometrial carcinoma cell lines (AMEC-1, RL95-2). The VDR was detected in 14 of the 21 endometrial carcinoma specimens. The growth of RL95-2 cells expressing VDR was inhibited to 44% when cultured with 50 nM 1,25(OH)2D3 for 6 days. In contrast, the growth of AMEC-1 cells not expressing VDR was completely uninhibited even when cultured with 100 nM 1,25(OH)2D3 for 6 days. The RL95-2 cells exposed to 50 nM 1,25(OH)2D3 for 6 days had an increasing expression for 52.5 kD or 45 kD cytokeratin polypeptide, and they became columnar with pronounced polarity and formed gland-like structures when cultured in collagen gel. These results suggest that endometrial adenocarcinoma is a target for 1,25(OH)2D3, which appears to function as a cell-differentiation-inducing agent for the treatment of endometrial cancer.

Receptors for 1,25-dihydroxyvitamin D3 in gynecologic neoplasms

To determine if gynecologic malignancies are candidates for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) therapy we measured vitamin D receptor (VDR) levels in 11 tumor specimens using a radiolabeled ligand-binding assay. VDR was demonstrated in 3 of 6 ovarian tumors and 1 of 1 uterine sarcomas, but not in endometrial tumors (2), cervical tumors (1), or Krukenberg tumors (1). Scatchard plots revealed that [3H]1,25(OH)2D3 was bound to a single class of high-affinity (Kd = 0.3 to 0.6 nM), saturable sites characteristic of authentic 1,25(OH)2D3 receptors. Specificity of binding activity for 1,25(OH)2D3, the active vitamin D3 metabolite, was demonstrated by failure of 25-hydroxy- and 24,25-dihydroxyvitamin D3 to compete effectively against 1,25(OH)2D3 binding in total cellular tumor extracts. The ovarian carcinoma cell line NIH:OVCAR3 was shown to possess VDR (binding capacity = 137 fmol/mg protein, Kd = 0.48 nM). A 3-day incubation of NIH:OVCAR3 cells with 100 nM 1,25(OH)2D3 resulted in 49% inhibition of cell growth. The growth inhibition of an ovarian carcinoma line and the observation that 36% of gynecologic tumors assayed were shown to be VDR-positive suggest that further study is warranted to delineate the mechanism and possible therapeutic aspects of 1,25(OH)2D3 action in gynecologic tumors.