抄録
We investigated cellular signaling cascades linked to estrogen-induced ER synthes is in mouse C2C12 myoblasts. By immunoblotting, ER was detected in the post-nuclear fraction with a corresponding molecular weight of 66 kDa. The amount of ER protein was dose-dependently (10−12-10−5 M increased after treatment with 17β-estradiol for 24 hours. 17α-estradiol (10−8M), the stereoisomer of 17β-estradiol, and a BSA-17β-estradiol-conjugate which is incapable of penetrating the plasma membrane, mimicked the increasing effects on ER. The level of ER expression was reduced by an ERK1/2 inhibitor, PD 98059(10μM), or a specific p38 inhibitor, SB 203580 (10μM) regardless of the presence of estradiol. Using 35S-methionine for immunoprecipitation, newly-synthesized ER was increased by 17β-estradiol. Novo-synthesis of ER was further increased by the protein kinase C (PKC) activator, TPA (1μM). These results suggest that ERs located at the plasma membrane of mouse skeletal myoblast cell are a target of estrogen's actions. The estrogen-stimulated ER synthesis involves the PKC/MAPK signaling system, thereby presumably regulating the proliferation process. However, somewhat contra-intuitively, up-regulation of estrogen receptor was also observed in the mouse skeletal muscle treated with antiestrogens, such as tamoxifen and ICI182780. [J Physiol Sci. 2006;56 Suppl:S147]
