Cross-Talk between Estrogen Receptors and Insulin-Like Growth Factor-I Receptor in Endometrial Cells

The endometrium is a target tissue of estrogens. Through estrogen receptor (ER), estrogens stimulate proliferation of the endometrial cell. In addition to 17β-estradiol binding, estrogen receptor (ER) transcriptional activity can be controlled by intracellular kinase signaling pathways activated by growth factors. IGF-I is a critical regulator of uterine growth, and locally produced uterine IGF-I can mediate the effects of 17β-estradiol (E2) on growth and cellular proliferation. Furthermore, Wnt and estrogen signaling represent important regulatory pathways, each controlling a wide range of biological processes. Estrogen in an ER-independent manner rapidly up-regulates the expression of Wnts of the Wnt family and frizzled-receptors of the Wnt receptor family in the mouse uterus. One of the mechanisms by which Wnts mediate canonical signaling involves stabilization of intracellular β-catenin. Recently, a novel link among the PI3K, wnt, and steroid hormone pathways has been delineated, suggesting the importance of cross-talk among these elements. Recently, we have successfully established immortalized human endometrial cells by infection of endometrial cells with retrovirus containing human telomerase reverse transcriptase (hTERT) (國科會計劃NSC96-2314-B- 182-016；PI：王馨世). While an increasing number of observations suggest potential convergence between these pathways, no direct evidence of their functional interaction has been reported. Our previous studies showed that a number of endometrial cancer cell lines induced β-catenin activity after treatment with estradiol (0.1 μM) or IGF-I (30 ng/ml). Additionally, the increased activity of β-catenin was also induced by LiCl (a GSK3β inhibitor). In the next three years, we are going to perform the following studies using immortalized endometrial cells. Part I (the first year)： The study of IGFs-mediated transactivation of estrogen receptor α (ERα) through PI3K and cross-talk with β-catenin in immortalized endometrial cells. The aim of the first year of this study is to testify 1. if IGFs (IGF-I or IGF-II) enhance specific target genes of estrogen receptor α (ERα) --- estrogen-responsive finger protein (Efp). 2. if overexpression of IGF-1 receptor (IGF-1R) enhance ERα-mediated transcription. 3. if IGF-I regulates ERα-mediated transcription through PI3K. 4. if the PI3K inhibitor LY294002 inhibits phosphorylation of both Akt and GSK3β. 5. if inhibition of PI3K signaling results in decreased nuclear accumulation of β-catenin. 6. if inhibition of ERα activity by the PI3K inhibitor LY294002 is mediated through Akt and GSK3β. Part II (the second year)： The study of regulation of Wnt/β-catenin signaling by estrogen in immortalized endometrial cells. The aim of the second year of this study is to testify 1. if estrogen regulates early Wnt signaling (expression of Wnt1, Wnt3, Wnt4, Wnt5a, Wnt7a, and Wnt7b) and expression of extracellular surface receptors frizzled (Fz) genes (Fz2, Fz4, Fz6, and Fz7). 2. if expression of secreted frizzled-related protein-2 (SFRP-2) gene is suppressed by estrogen. 3. if estrogen activates canonical Wnt signaling (β-catenin). 4. if estrogen stimulates glycogen synthase kinase 3β (GSK3β) expression. 5. if estrogen stabilizes β-catenin (mediated through GSK3β). 6. if estrogen induces the expression of β-catenin-specific target genes (the expression of known β-catenin/TCF target genes), including cyclin D1 (Ccnd1) and c-myc (Myc) genes. Part III (the third year)： The study of involvement of glycogen synthase kinase 3β (GSK3β) in Wnt/β-catenin pathway modulated by estrogens and progestins in decidualization of immortalized endometrial cells. The aim of the third year of this study is to testify 1. if progesterone inhibits the ERE activity induced by IGF-I. 2. if progesterone reduces glycogen synthase kinase 3β (GSK3β) expression. 3. if progesterone induces β-catenin expression. 4. if progesterone-induced β-catenin expression is through glycogen synthase kinase 3β (GSK3β). 5. if progesterone inhibits the expression of β-catenin-specific target genes (the expression of known β-catenin/TCF target genes), including cyclin D1 (Ccnd1) and c-myc (Myc) genes.

Project ID:PC9902-0298
External Project ID:NSC97-2314-B182-014-MY3