Molecular tools to reestablish progestin control of endometrial cancer cell proliferation.

Abstract

Endometrial cancers often arise in a setting of estrogen stimulation unopposed by the differentiating effects of progesterone. Our laboratory and others have previously shown that progesterone receptor down-regulation or perturbation of progesterone receptor isoform A or B expression is associated with the development of poorly differentiated endometrial cancers that are not growth inhibited by progestins. The purpose of these studies was to reestablish high progesterone receptor isoform A and B gene expressions in such endometrial cancer cells and to examine the effects of progestin treatment on cell growth and metastatic potential after this transformation. To induce high levels of expression of the progesterone receptor isoforms in KLE and Hec50 endometrial cancer cells, adenoviral vectors encoding the genes for progesterone receptor isoforms A and B were created. The characteristic ability of cancer cells to grow independently of anchorage to the surrounding solid matrix was measured by counting colony formation on soft agar for 8 to 14 days. Cell proliferation in response to a time course of progestin treatment was tested with flow cytometry. After treatment with a control vector without a progesterone receptor--encoding insert, no effect of progestin treatment on cell proliferation was found; after treatment with vectors encoding progesterone receptor isoform A or B, however, progestin treatment resulted in significant inhibition of cell growth. The anchorage-independent cell growth on soft agar assay showed that by 8 to 14 days the number of cell colonies was reduced by 50% relative to control preparations in the presence of progesterone receptor isoform A plus progestin (P <.0001, both Hec50 and KLE cell lines) and by 90% in the presence of progesterone receptor isoform B plus progestin (P <.0001, both Hec50 and KLE cell lines). Progestin treatment also resulted in a time-dependent reduction in cell proliferation as measured by flow cytometry. Although transfection with both progesterone receptor isoforms A and B reduced cell proliferation according to our assays, progesterone receptor isoform B caused a much more dramatic decrease in cell growth (P =.001, Hec50 cells; P <.0001, KLE cells). In poorly differentiated endometrial cancer cells that are resistant to progestin therapy, adenovirus-induced expressions of progesterone receptors A and B reestablish progestin control of endometrial cancer cell proliferation.