The crosstalk between the PI3K/Akt signal and Skp2 in prostate cancer progression

描述(申请人提供)：由于PTEN肿瘤抑制功能的丧失导致Akt异常激活是人类癌症中的一种普遍事件，并与癌症转移有关，因此确定PTEN/PI3K/Akt通路下游推动癌症进展和转移的关键效应是很重要的。利用生化方法和小鼠遗传模型，我们确定Skp2是一种重要的Akt底物，在PTEN/Akt介导的肿瘤发生中起关键作用。Skp2(S相激酶相关蛋白-2)是一种F-box蛋白，是Skp2 SCF复合体中负责底物识别的E3连接酶成分。Skp2过表达诱导细胞周期进入，而p27的降解参与了Skp2介导的细胞周期进程。虽然Skp2在许多人类癌症中过表达，并与癌症转移相关，但目前尚不清楚Skp2在肿瘤进展过程中如何过表达，以及它的致癌活性是如何调节的。我们的研究首次提出Akt激酶在S72使Skp2磷酸化，Skp2 S72磷酸化是协调Skp2 E3连接酶活性和致癌功能的分子开关。本应用的目的是确定PTEN/PI3K/Akt信号和Skp2 S72磷酸化之间的功能串扰在前列腺癌进展和转移中的作用。该应用的中心假设是PI3K/Akt对Skp2 S72的磷酸化在前列腺癌的进展和转移中起关键作用。我们的中心假设是在我们强大的初步数据的基础上提出的。这项研究的理论基础是，一旦Skp2 S72磷酸化在前列腺癌进展和转移中的重要作用得到确认和确立，前列腺癌的更好治疗或靶点就可以实现。我们计划验证我们的中心假说，并通过追求以下特定目标来实现这一应用的目标：目的1)确定PI3K/Akt通路调控Skp2基因表达和活性的分子机制。目的2)探讨Skp2 S72磷酸化在前列腺癌发生发展中的作用。目的3)确定Akt和Skp2在细胞迁移和侵袭中的功能串扰。目的4)探讨Skp2和Skp2 S72磷酸化在前列腺癌转移中的作用。这项提案工作具有创新性，因为它首次提出Akt是Skp2的一种激酶，并且Akt对Skp2 E3连接酶活性、胞浆定位和致癌功能至关重要。重要的是，我们的研究表明，在前列腺癌动物模型中，Skp2是PTEN/PI3K/Akt信号的关键下游效应因子。根据受到尊重的结果，这项提案中的工作组合有望共同揭示Skp2 S72磷酸化在前列腺癌进展和转移中的关键作用。这些结果将产生重要的积极影响，因此可能为前列腺癌的治疗提供潜在的治疗靶点。我们的结果也将从根本上促进我们目前对前列腺癌如何发展和进一步进入转移阶段的理解。 公共卫生相关性：尽管在前列腺癌领域已经进行了广泛的研究，但前列腺癌如何发展并进一步发展为转移性前列腺癌仍不清楚。我们的研究表明，在前列腺癌中过度表达的癌蛋白Skp2的S72磷酸化是由PI3K/Akt信号诱导的，对其E3连接酶活性和致癌功能至关重要。了解Skp2和Skp2 S72磷酸化在前列腺癌进展和转移中的重要作用，可能为前列腺癌的治疗提供重要的指导意义。

DESCRIPTION (provided by applicant): As loss of PTEN tumor suppressive function resulting in aberrant Akt activation is a prevalent event in human cancers and associated with cancer metastasis, it is important to identify the key effector downstream of the PTEN/PI3K/Akt pathway that drives cancer progression and metastasis. Using the biochemical approaches and mouse genetic models, we identified Skp2 as an important Akt substrate that plays a critical for PTEN/Akt-mediated tumorigenesis. Skp2 (S-phase kinase associated protein-2), an F-box protein, is an E3 ligase component of Skp2 SCF complex responsible for substrate recognition. Skp2 overexpression induces cell cycle entry, and the degradation of p27 is responsible for Skp2-mediated cell cycle progression. Although Skp2 is overexpressed in numerous human cancers and associates with cancer metastasis 1,2, it remains unclear how Skp2 overexpression occurs during cancer progression and how its oncogenic activity is regulated. Our study provides for the first time that Akt kinase phosphorylates Skp2 at S72 and Skp2 S72 phosphorylation is a molecular switch that orchestrates Skp2 E3 ligase activity and oncogenic functions. The objective of this application is to determine the functional crosstalk between PTEN/PI3K/Akt signal and Skp2 S72 phosphorylation in prostate cancer progression and metastasis. The central hypothesis of the application is that Skp2 S72 phosphorylation by PI3K/Akt is critical for prostate cancer progression and metastasis. Our central hypothesis has been formulated on the basis of our strong preliminary data. The rationale of the proposed research is that, once the important role of Skp2 S72 phosphorylation is confirmed and established in prostate cancer progression and metastasis, the better treatment or target for prostate cancer can be achieved. We plan to test our central hypothesis and accomplish the objective of this application by pursuing the following specific aims: Aim 1) To determine the molecular mechanism by which Skp2 gene expression and activity are regulated by the PI3K/Akt pathway. Aim 2) To determine the potential role of Skp2 S72 phosphorylation in prostate cancer progression. Aim 3) To determine the functional crosstalk between Akt and Skp2 in cell migration and invasion. Aim 4) To determine the potential role of Skp2 and Skp2 S72 phosphorylation in prostate cancer metastasis. This proposal work is innovative, because it provides for the first time that Akt is a kinase for Skp2 and that Skp2 S72 phosphorylation by Akt is critical for Skp2 E3 ligase activity, cytosolic localization, and oncogenic functions. Importantly, our study reveals that Skp2 is a critical downstream effector for the PTEN/PI3K/Akt signal in animal models of prostate cancers. With respected outcomes, the combination of work in this proposal is collectively expected to uncover the critical role Skp2 S72 phosphorylation in prostate cancer progression and metastasis. Such results will have an important positive impact and may therefore provide a potentially therapeutic target for prostate cancer treatment. Our results will also fundamentally advance our current understandings of how prostate cancer develops and further progresses into the metastasis stage. PUBLIC HEALTH RELEVANCE: Although the extensive studies have been made in the field of prostate cancer, how prostate cancer develops and further progresses into metastatic prostate cancer is still unclear. Our study reveals that the S72 phopshorylation of Skp2, an oncoprotein overexpressed in prostate cancer, is induced by the PI3K/Akt signal and is critical for its E3 ligase activity and oncogenic functions. Understanding the important role of Skp2 and Skp2 S72 phopshorylation in prostate cancer progression and metastasis may provide an important therapeutic implication for human prostate cancers.