Dehydroepiandrosterone (DHEA) is believed to have an anti-tumor effect, as well as anti-inflammatory, antioxidant, and anti-aging effects. To clarify the possible inhibitory action of DHEA on pituitary tumor cells, we tested the effects of DHEA, alone or in combination with the nuclear factor-κB (NF-κB) inhibitor parthenolide (PRT), on AtT20 corticotroph cell growth and function both in vitro and in vivo. We found that, in vitro, DHEA and PRT had potent inhibitory effects on pro-opiomelanocortin and NF-κB-dependent gene expression. They also suppressed the transcription activity of survivin, a representative anti-apoptotic factor, and induced apoptosis in this cell line. Furthermore, using BALB/C nude mice with xenografts of AtT20 cells in vivo, we found that the combined administration of DHEA and PRT significantly attenuated tumor growth and survivin expression. The treatment also decreased the elevated plasma corticosterone levels and ameliorated the malnutrition induced by tumor growth. Altogether, these results suggested that combined treatments of DHEA and PRT potently inhibit the growth and function of corticotroph tumor cells both in vitro and in vivo. This effect may, at least partly, be caused by the suppressive effects of these compounds, such as survivin and other inhibitor of apoptosis proteins, on NF-κB-mediated gene transcription.
T Taguchi, T Takao, Y Iwasaki, M Nishiyama, K Asaba and K Hashimoto
R Kurotani, S Yoshimura, Y Iwasaki, K Inoue, A Teramoto and RY Osamura
The pituitary-specific POU-homeodomain transcription factor, Pit-1, is known to regulate the expression of the GH gene in somatotropes, prolactin (PRL) in lactotropes, and TSH in thyrotropes. It is not normally expressed in corticotropes or gonadotropes. We addressed the question of whether exogenous Pit-1 was sufficient to induce ectopic transcription of the GH gene in the corticotropic cell line, AtT-20, or the gonadotropic cell line, alpha T3-1. A fusion gene composed of enhanced green fluorescent protein gene and human Pit-1 cDNA was transfected into AtT-20 and alpha T3-1 cells. The endogenous mouse GH mRNA was induced in three of nine AtT-20 cell lines and one of three alpha T3-1 cell lines containing the fusion gene. A small amount of GH protein was also detected in these cell lines. These data indicate that transfected Pit-1 is capable of inducing transcription of the GH gene in AtT-20 cells and alpha T3-1 cells. These data also suggest that synergistic co-factors might be required to transcribe the GH gene effectively for translation into GH protein. Furthermore, our findings support the hypothesis that the function of anterior pituitary cells is determined by the combinatorial action of specific transcription factors.