Androgenic Inactivation of FOXO1 in Prostate Cancer

描述(申请人提供)：前列腺癌是美国癌症死亡的第二大原因。前列腺癌细胞的生长和存活依赖于雄激素。雄激素的促有丝分裂作用与其对细胞周期调控分子的调控有关，如细胞周期蛋白依赖性激酶2和4(CDK2和CDK4)。然而，雄激素介导的细胞存活的分子机制还没有完全阐明。我们和其他人已经证明，雄激素通过拮抗肿瘤抑制蛋白PTEN的功能来提高前列腺癌的存活率。进一步的研究表明，雄激素通过直接抑制PTEN下游的关键靶点叉头转录因子FOXO1(FKHR)的功能来阻断PTEN信号转导。我们的初步数据表明，在体内外，CDK2与FOXO1相互作用并磷酸化FOXO1。CDK2通过丝氨酸249的磷酸化抑制FOXO1的功能。重要的是，CDK2介导的FOXO1的磷酸化和抑制可以在化疗药物和辐射诱导的DNA损伤后逆转。鉴于雄激素介导的增殖和存活的作用以及雄激素治疗和放射治疗相互作用的抗肿瘤作用，我们推测CDK2介导的FOXO1失活在雄激素刺激的前列腺癌细胞的增殖、存活和氧化应激中起重要作用。为了验证这一假说，我们提议确定(1)CDK2介导的FOXO1磷酸化是否在雄激素刺激的前列腺癌细胞的增殖和存活中发挥重要作用；(2)雄激素诱导的FOXO1磷酸化是否抑制前列腺癌细胞中FOXO1的转录活性；(3)FOXO1的激活是否是介导雄激素去除和放射治疗协同抗肿瘤作用的关键因素。这项工作的发现将为雄激素诱导前列腺癌细胞增殖和存活的工作机制提供新的见解。此外，它们还应加强我们对雄激素消融和放射治疗在临床上的治疗优势的潜在机制的理解。

DESCRIPTION (provided by applicant): Prostate cancer is the second leading cause of cancer death in the United States. Cancer cells in the prostate depend on androgens for growth and survival. Mitogenic effects of androgens have been linked to their modulation of cell cycle regulatory molecules such as cyclin-dependent kinase 2 and 4 (CDK2 and CDK4). However, the molecular mechanisms for androgen-mediated cell survival are not fully elucidated. We and others have shown that androgens promote prostate cancer survival by antagonizing the function of PTEN, a tumor suppressor protein. Further studies have revealed that androgens block PTEN signaling by directly inhibiting the function of the forkhead transcription factor FOXO1 (FKHR), a key downstream target of PTEN. Our preliminary data demonstrate that CDK2 interacts with and phosphorylates FOXO1 in vitro and in vivo. CDK2 inhibits the function of FOXO1 through phosphorylation of serine 249. Importantly, CDK2- mediated phosphorylation and inhibition of FOXO1 can be reversed upon DNA damage induced by chemotherapeutic agents and irradiation. In view of the roles of androgen-mediated proliferation and survival and the anti-tumor effect of the interaction between androgen ablation and radiation therapy in the clinic, we hypothesize that CDK2-mediated inactivation of FOXO1 plays an important role in androgen-stimulated proliferation, survival, and oxidative stress in prostate cancer cells. To test this hypothesis, we propose to determine (1) whether CDK2-mediated phosphorylation of FOXO1 plays an essential role in androgen- stimulated proliferation and survival of prostate cancer cells; (2) whether androgen-induced phosphorylation of FOXO1 inhibits FOXO1 transcriptional activity in prostate cancer cells; (3) whether activation of FOXO1 is a key factor that mediates the synergistic anti-tumor effect of androgen ablation and radiation therapy. The findings from this work will provide new insights into the working mechanisms of androgen-induced proliferation and survival of prostate cancer cells. Moreover, they should enhance our understanding of the underlying mechanisms of the therapeutic advantage of androgen ablation and radiation therapy in the clinic.