Phosphatidylinositol 3-Kinase-AKT-Mammalian Target of Rapamycin Pathway Is Essential for Neuroendocrine Differentiation of Prostate Cancer*
- 1 Supported by grants from the Department of Defense Prostate Cancer Research Program and the American Cancer Society. To whom correspondence should be addressed: Dept. of Pathology, Box 626, University of Rochester Medical Center, 601 Elmwood Ave., Rochester, NY 14642. Tel.: 585-275-8526; Fax: 585-273-3637; E-mail: Jiaoti_Huang{at}urmc.rochester.edu.
Abstract
Hormonal therapy of prostate cancer, by inhibiting androgen production and/or androgen function, is the treatment of choice for advanced prostate cancer. Although most patients respond initially, the effect is only temporary, and the tumor cells will resume proliferation in an androgen-deprived environment. The mechanism for androgen-independent proliferation of cancer cells is unclear. Hormonal therapy induces neuroendocrine differentiation of prostate cancer cells, which is hypothesized to contribute to tumor recurrence by a paracrine mechanism. We studied signal transduction pathways of neuroendocrine differentiation in LNCaP cells after androgen withdrawal, and we showed that both the phosphatidylinositol 3-kinase-AKT-mammalian target of rapamycin pathway and ERK are activated, but only the former is required for neuroendocrine differentiation. A constitutively active AKT promotes neuroendocrine differentiation and a dominant negative AKT inhibits it. Activation of AKT by IGF-1 leads to neuroendocrine differentiation, and neuroendocrine differentiation induced by epinephrine requires AKT activation. We also show that the AKT pathway is likely responsible for neuroendocrine differentiation in DU145, an androgen-independent prostate cancer cell line. Therefore, our study demonstrated a novel function of the AKT pathway in prostate cancer progression and identified potential targets that may be explored for the treatment of androgen-independent cancer.
Footnotes
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↵2 The abbreviations used are: PC, prostate cancer; AI, androgen-independent; NE, neuroendocrine; NED, neuroendocrine differentiation; AR, androgen receptor; S6K, S6 kinase; IGF-1, insulin-like growth factor-1; mTOR, mammalian target of rapamycin; FBS, fetal bovine serum; ERK, extracellular signal-regulated kinase; MEK, mitogen-activated protein kinase/ERK kinase; NSE, neuron-specific enolase; PI3K, phosphatidylinositol 3-kinase; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HB-EGF, heparin-binding epidermal growth factor; C-FBS, charcoal-treated (androgen-deprived) FBS.
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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- Received September 5, 2006.
- Revision received November 20, 2006.
- The American Society for Biochemistry and Molecular Biology, Inc.
