Induction of mammotroph development by a combination of epidermal growth factor,insulin, and estradiol-17beta in rat pituitary tumor GH3 cells

Several reports have indicated that prolactin-secreting cells (PRL cells) are generated from growth hormone-secreting cells (GH cells). We have shown that treatment with a combination of epidermal growth factor (EGF), insulin, and estradiol-17beta (E (2)) induces the appearance of PRL cells in pituitary tumor GH3 cells. The aim of the present study was to clarify the involvement of mitosis in the cytogenesis of PRL cells in rat pituitary and GH3 cells. The effects of the treatment with EGF, insulin and E(2) on DNA-replication were studied by detecting the uptake of bromodeoxyuridine (BrdU) into the nucleus. In cultured rat pituitary cells, BrdU-labeled PRL cells were observed irrespective of the hormone treatment. In GH3 cells, BrdU-labeled GH cells and mammosomatotrophs (MS cells) were detected; BrdU-labeled PRL cells were not detected, however, when GH3 cells were treated with BrdU for 3 hr and then immediately examined for BrdU-labeling. BrdU-labeled PRL cells were found only when GH3 cells treated with BrdU were allowed to grow for another 3 days. This finding suggests that during the additional 3-day culture, BrdU-labeled PRL cells were generated from BrdU-labeled cells other than PRL cells. These results indicate that PRL cells are transdifferentiated from GH cells or MS cells in GH3 cells by a combined treatment with EGF, insulin and E(2), while PRL cells in rat pituitaries are able to proliferate in response to the hormone treatment. Thus, there may be two pathways for cytogenesis of PRL cells: the transdifferentiation of GH cells or MS cells, and a self-duplication of PRL cells.