Medroxyprogesterone Acetate Induces Cell Proliferation through Up-Regulation of Cyclin D1 Expression via Phosphatidylinositol 3-Kinase/Akt/Nuclear Factor-κB Cascade in Human Breast Cancer Cells

• Published in: Endocrinology (Philadelphia) 2005-11, Vol.146 (11), p.4917-4925
• Main Authors: Saitoh, Maki, Ohmichi, Masahide, Takahashi, Kazuhiro, Kawagoe, Jun, Ohta, Tsuyoshi, Doshida, Masakazu, Takahashi, Toshifumi, Igarashi, Hideki, Mori-Abe, Akiko, Du, Botao, Tsutsumi, Seiji, Kurachi, Hirohisa
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase; Acetic acid; AKT protein; Attenuation; Biological and medical sciences; Breast cancer; Cell growth; Cell proliferation; Cyclin D1; Fundamental and applied biological sciences. Psychology; Gynecology. Andrology. Obstetrics; Inhibition; Kinases; Mammary gland diseases; Medical sciences; Medroxyprogesterone acetate; NF-κB protein; Nuclear transport; Phosphorylation; Progesterone; Protein folding; Regulatory sequences; Translocation; Tumors; Up-regulation; Vertebrates: endocrinology; Wortmannin
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2004-1535

The mechanism of medroxyprogesterone acetate (MPA)-induced cell proliferation in human breast cancer cells remains elusive. We examined the mechanism by which MPA affects the cyclin D1 expression in progesterone receptor (PR)-positive T47D human breast cancer cells. MPA (10 nm) treatment for 48 h induced proliferation of the cells (1.6-fold induction). MPA induced cyclin D1 expression (3.3-fold induction), and RU486, a selective PR antagonist, blocked the MPA-induced cell proliferation and cyclin D1 expression (23% inhibition). MPA increased both the protein level (2.2-fold induction) and promoter activity (2.7-fold induction) of cyclin D1 in MCF-7 cells transfected with PRB but not with PRA. Although MPA transcriptionally activated cyclin D1 expression, cyclin D1 promoter does not have progesterone-responsive element-related sequence. We further examined the mechanism for the regulation of the cyclin D1 expression. Because the cyclin D1 promoter contains three putative nuclear factor-κB (NFκB)-binding motifs and NFκB is a substrate of Akt, we investigated the effect of the phosphatidylinositol 3-kinase (PI3K)/Akt/NFκB cascade on the responses of cyclin D1 to MPA. MPA induced the transient phosphorylation of Akt (2.7-fold induction at 5 min), and treatment with PI3K inhibitor (wortmannin) attenuated the MPA-induced up-regulation of cyclin D1 expression (40% inhibition) and cell proliferation (40% inhibition). MPA also induced phosphorylation of inhibitor of NFκBα (IκBα) (2.3-fold induction), and treatment with wortmannin attenuated the MPA-induced IκBα phosphorylation (60% inhibition). Treatment with an IκBα phosphorylation inhibitor (BAY 11-7085) or a specific NFκB nuclear translocation inhibitor (SN-50) attenuated the MPA-induced up-regulation of both cyclin D1 expression (80 and 50% inhibition, respectively) and cell proliferation (55 and 34% inhibition, respectively). Because MPA induced a transient phosphorylation of Akt and the cyclin D1 promoter contains no progesterone-responsive element-related sequence, the MPA-induced cell proliferation through PRB by up-regulation of cyclin D1 expression via the PI3K/Akt/NFκB cascade may be a nongenomic mechanism.