PTEN Nuclear-Cytoplasmic Localization in Breast Cancer

描述（由申请人提供）：肿瘤抑制基因，如PTEN，已被证明在散发性乳腺癌发生中发挥重要的体细胞作用。PTEN的脂质磷酸酶活性作为细胞质PISK/Akt途径的负调节剂的作用是众所周知的。免疫组织化学研究首次提示PTEN存在于细胞核中。然而，关于非细胞质PTEN在调节细胞通路中的作用知之甚少。越来越多的遗传学、病理学和生物化学证据表明，PTEN的核质分配在肿瘤发生中起作用。迄今为止，关于PTEN核输入的机制或其对核信号通路的影响，特别是在致癌过程中核与胞质信号之间的串扰，知之甚少。我们已经鉴定了PTEN中的非传统核定位信号（NLS），并且表明这些NLS对于与主要穹窿蛋白（MVP）（一种潜在的细胞质-核穿梭蛋白）的相互作用至关重要。我们和其他人以前曾报道过许多浸润性癌症（包括乳腺癌）细胞核中Akt的激活增强。此外，侵袭与核PTEN表达的丧失相关，表明PTEN/Akt信号传导的调节和在核中的定位在肿瘤进展中可能是重要的。我们已经确定并表征了Akt的功能性核输出结构域，并证明核Akt激活足以诱导体外细胞迁移。我们的数据表明，PTEN能够调节Akt亚细胞定位和激活在细胞核中，从而定义了一个机制，在肿瘤进展的核PTEN损失。因此，我们推测，细胞周期的停滞和改变，在细胞核-细胞质分配的PTEN和其调节的核和细胞质Akt是致癌的机制，需要核的PTEN。为了解决我们的假设，我们建议：1：检查核PTEN在细胞功能和维持细胞周期阻滞中的作用; 2：确定核PTEN定位的机制; 3：评估核PTEN作为核Akt活性和定位的负调节剂的作用。当这些研究完成后，我们将有一个更大的基础知识的作用，核PTEN作为一个肿瘤抑制剂在乳腺癌的发生。这些数据还可以帮助乳腺癌药物的开发，并为治疗和预防提供新的靶点。

DESCRIPTION (provided by applicant): Tumor suppressor genes, such as PTEN, have been shown to play an important somatic role in sporadic breast carcinogenesis. The role of PTEN's lipid phosphatase activity as a negative regulator of the cytoplasmic PISK/Akt pathway is well known. Immunohistochemical studies were the first to suggest that PTEN exists in the nucleus. However, little is known about the role of non-cytoplasmic PTEN in regulating cellular pathways. Accumulating genetic, pathologic and biochemical evidence strongly suggests that nuclear-cytoplasmic partitioning of PTEN plays a role in carcinogenesis. To date, little is known about the mechanism of PTEN nuclear import or its impact on nuclear signaling pathways, particularly the cross talk between the nuclear and cytoplasmic signaling during carcinogenesis. We have identified non-traditional nuclear localization signals (NLS) in PTEN and showed that these NLS are critical for interaction with Major Vault Protein (MVP), a potential cytoplasmic-nuclear shuttling protein. We and others have previously reported enhanced activation of Akt in the nucleus of many invasive cancers, including breast malignancies. Additionally, the invasion has been associated with loss of nuclear PTEN expression, indicating that regulation of PTEN/Akt signaling and localization in the nucleus may be important in tumor progression. We have identified and characterized a functional nuclear export domain of Akt and demonstrated that nuclear Akt activation is sufficient to induce cell migration in vitro. Our data suggest that PTEN is capable of regulating Akt sub-cellular localization and activation in the nucleus, thereby defining a mechanism for nuclear PTEN loss in tumor progression. Thus, we hypothesize that nuclear PTEN is required for cell cycle arrest and alterations in the nuclear-cytoplasmic partitioning of PTEN and its regulation of nuclear and cytoplasmic Akt is a mechanism of carcinogenesis. To address our hypothesis, we propose to: 1: examine the role of nuclear PTEN in cellular functions and in the maintenance of cell cycle arrest; 2: determine the mechanism of nuclear PTEN localization; 3: evaluate the role of nuclear PTEN as a negative regulator of nuclear Akt activity and localization. When these studies complete, we will have a greater fundamental knowledge of the role of nuclear PTEN as a tumor suppressor in breast carcinogenesis. These data could also aid in drug development for breast cancer as well as provide novel targets for therapy and prevention.