Expression and action of transforming growth factor beta (TGFβ1, TGFβ2, TGFβ3) in normal bovine ovarian surface epithelium and implications for human ovarian cancer

Abstract The majority of ovarian tumors are derived from the single layer of epithelial cells on the surface of the ovary termed the ovarian surface epithelium (OSE). Stromal cell–OSE interactions are postulated to be an important aspect of normal OSE biology and the biology of ovarian cancer. Transforming growth factor beta (TGFβ) has been shown to often be a mesenchymal cell-derived growth factor that mediates stromal cell–epithelial cell interactions in a variety of different tissues. The current study investigates the expression and action of TGFβ isoforms (TGFβ1, TGFβ2, and TGFβ3) in OSE and the underlying stroma in both normal bovine and human tumor tissues. Normal bovine ovaries are similar to human ovaries and are used as a model system to investigate normal OSE and stromal cell functions. All three TGFβ isoforms and their receptor, transforming growth factor beta receptor type II (TGFβRII), proteins were found to be detected in the OSE from normal bovine ovaries using immunohistochemistry. Ovarian stromal tissue also contained positive immunostaining for TGFβ isoforms and TGFβRII. RNA was collected from normal bovine OSE and ovarian stromal cells to examine TGFβ gene expression. TGFβ1, TGFβ2, and TGFβ3 transcripts were detected in both freshly isolated and cultured bovine OSE and stromal cells by a sensitive quantitative polymerase chain reaction assay. TGFβ1 and TGFβ2 mRNA levels were found to be present at similar levels in freshly isolated OSE and stroma. Interestingly, TGFβ3 mRNA levels were significantly higher in freshly isolated OSE than stromal cells. All but TGFβ3 mRNA in OSE increased when the cells were cultured. Observations indicate that normal bovine OSE and stroma cells express the three TGFβ isoforms in vivo and in vitro. Human ovarian tumors from stage II, stage III and stage IV cases were found to express TGFβ1, TGFβ2, TGFβ3 and TGFβRII protein primarily in the epithelial cell component by immunohistochemistry analysis. The stromal cell component of the human ovarian tumors contained little or no TGFβ or TGFβRII immunostaining. TGFβ actions on bovine OSE and stromal cells were also investigated. TGFβ was found to inhibit the growth of OSE, but not stromal cells. To further examine the actions of TGFβ on OSE, the expression of two growth factors previously shown to be expressed by OSE were analyzed. TGFβ1 was found to stimulate the expression of both keratinocyte growth factor (KGF) and kit ligand/stem cell factor (KL) by bovine OSE. Therefore, TGFβ actions on OSE will likely promote a cascade of cell–cell interactions and cellular responses involving multiple growth factors. The effects of regulatory agents on TGFβ expression by the bovine OSE were examined. Transforming growth factor alpha (TGFα) stimulated TGFβ1 expression, TGFβ1 stimulated TGFβ2 expression, and follicle stimulating hormone (FSH) stimulated TGFβ3 expression. These results demonstrate that TGFβ isoforms are regulated differently by the regulatory agents tested. In summary, all the TGFβ isoforms are differentially expressed by the OSE and TGFβ appears to have an important role in regulating OSE and possibly stromal–OSE interactions. A complex network of endocrine and paracrine interactions appears to influence the expression and actions of TGFβ on OSE. Abnormal expression and/or action of TGFβ is postulated to in part be involved in the onset and progression of ovarian cancer.