Nongenomic Androgen Activation of Phosphatidylinositol 3-Kinase/Akt Signaling Pathway in MC3T3-E1 Osteoblasts

Authors

  • Hong-Yo Kang,

    1. The Center for Menopause and Reproductive Medicine Research, Chang Gung University/Memorial Hospital, Kaohsiung, Taiwan
    2. Graduate Institute of Clinical Medical Sciences, Chang Gung University, Kaohsiung, Taiwan
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  • Chung-Lung Cho,

    1. Department of Biological Science, National Sun Yat-sen University, Kaohsiung, Taiwan
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  • Kai-Lieh Huang,

    Corresponding author
    1. The Center for Menopause and Reproductive Medicine Research, Chang Gung University/Memorial Hospital, Kaohsiung, Taiwan
    2. Department of Biological Science, National Sun Yat-sen University, Kaohsiung, Taiwan
    • Address reprint requests to: Ko-En Huang, MD, and Chawnshang Chang, PhD, Graduate Institute of Clinical Medical Science, Chang Gung University, 16-4F, No. 123-9, Tao-Pei Road, Niao-Sung Hsiung, Kaohsiung 866, Taiwan
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  • Jyh-Chwan Wang,

    1. The Center for Menopause and Reproductive Medicine Research, Chang Gung University/Memorial Hospital, Kaohsiung, Taiwan
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  • Yueh-Chiang Hu,

    1. Departments of Pathology, Urology, and Radiation Oncology, The Cancer Center, George Whipple Lab for Cancer Research, University of Rochester, Rochester, New York, USA
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  • Hui-Kuan Lin,

    1. Departments of Pathology, Urology, and Radiation Oncology, The Cancer Center, George Whipple Lab for Cancer Research, University of Rochester, Rochester, New York, USA
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  • Chawnshang Chang,

    1. Departments of Pathology, Urology, and Radiation Oncology, The Cancer Center, George Whipple Lab for Cancer Research, University of Rochester, Rochester, New York, USA
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  • Ko-En Huang

    1. The Center for Menopause and Reproductive Medicine Research, Chang Gung University/Memorial Hospital, Kaohsiung, Taiwan
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  • The authors have no conflict of interest

Abstract

Androgens have important effects on the bone metabolism. However, the effect and mechanism of androgen action on the osteoblasts remains unknown. Here we showed that androgens increase phosphorylation and nuclear translocation of Akt. siRNA-AR prevented androgen-induced Akt activation in MC3T3-E1 cells. This suggests that nongenomic androgen activation of Akt is mediated by androgen receptor in osteoblasts.

Introduction: Androgens have important effects on the human skeleton in both males and females. However, the mechanism of androgen action on bone metabolism remains unknown. The aims of this study were to determine the effect and mechanism of androgen action on the osteoblast cells.

Materials and Methods: Here we showed that 5α-dihydrotestosterone (DHT) accelerates cell growth of the MC3T3-E1 cell line in a time- and dose-dependent manner. The specific phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor LY294002 and kinase-deficient Akt mutant can repress the androgen effect on MC3T3-E1 cells. Western blot analysis showed that DHT, 17β-estradiol, and testosterone (T) induce a rapid and transient phosphorylation of Akt in MC3T3-E1 cells. This activation reached to a plateau after 15 minutes and gradually diminished after 60 minutes of DHT treatment.

Results: Fluorescence microscopy showed a distinct increase in immunostaining intensity in the nuclear interior after androgen treatment but no change in the subcellular distribution of Akt when the cells were pretreated with hydroxyflutamide (HF) or LY294002. In addition, small interfering RNA against androgen receptor (siRNA-AR) prevented DHT-induced Akt phosphorylation and cell growth.

Conclusion: These findings represents the first physiological finding to indicate how steroid hormones such as androgens can mediate the nuclear localization of Akt/PKB in osteoblasts that has previously mainly been linked to growth factor-induced events occurring at the plasma membrane level.

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