A new regulator for Wnt/beta-catenin signaling and prostate tumorigenesis

描述(由申请人提供)：积累的证据表明Wnt/？-catenin通路在前列腺发育和肿瘤发生中具有重要作用。细胞质和核连环蛋白的失调已被证明是肿瘤发生中的一个关键事件。因此，肿瘤细胞中β-连环蛋白和破坏复合体成分的突变的发现证实了？-连环蛋白在人类肿瘤中的重要性。超过80%的结直肠癌存在抑癌基因APC的非活性突变。在肝细胞癌中也发现了Axin突变。此外，在多种人类恶性肿瘤中发现了GSK32靶点上四个丝氨酸/苏氨酸残基的点突变。有趣的是，在前列腺癌样本中，β-连环蛋白、APC和破坏复合体的其他成分的突变非常罕见。然而，在疾病进展过程中，核连环蛋白的增加在晚期前列腺癌中经常被观察到。因此，在前列腺癌的发生发展过程中，Wnt/β-catenin信号通路的调控可能有其他途径/机制起主导作用。在过去的研究中，我们发现LAPSER1，也被称为LZTS2(Leucine zipper putation Tumor Suppressor 2，亮氨酸拉链假定的肿瘤抑制因子2)，是一种新的-连环蛋白相互作用蛋白。人类LZTS2基因位于染色体10q24.3上。这一区域已被证明在包括前列腺癌在内的各种人类肿瘤中经常缺失。LZTS2蛋白的过表达影响β-连环蛋白的亚细胞定位，抑制其转录活性，抑制细胞生长。有趣的是，在LZTS2的C末端发现了一个功能丰富的HIV Rev样亮氨酸，CRM1/exportin调控的核输出信号(NES)。通过该NES位点，LZTS2可促进β-连环蛋白的核输出，降低细胞内核连环蛋白的水平。通过免疫组织化学方法，我们进一步证明LZTS2在前列腺腔上皮细胞胞浆中表达，并且在人前列腺癌组织中的表达显著降低。这些数据阐明了LZTS2作为一种新的调节因子在Wnt/？-catenin介导的转录、细胞生长和肿瘤发生中的重要作用。尽管Wnt/？-catenin信号通路在前列腺癌发生中的重要作用已被证实，但在前列腺癌细胞中？？-catenin调控失调的确切途径/机制仍不清楚。我们最近的研究发现，LZTS2是一种β-连环蛋白相互作用的蛋白，并调节？-连环蛋白的活性和细胞定位，这表明LZTS2是Wnt/？-连环蛋白信号通路的一个新的调节因子。因此，我们在这个修订的RO1应用中提出了一系列实验，以解决我们的中心假设，即LZTS2负调控Wnt/？-连环蛋白信号通路，其失调将激活Wnt/？-连环蛋白信号通路，并有助于肿瘤的发生。通过基因敲除小鼠模型研究LZTS2的生物学作用，检测LZTS2在人前列腺癌中的表达，研究LZTS2对Wnt/β-catenin信号的异常调节在前列腺癌发生发展中的作用。上述研究的目的在于阐明LZTS2在肿瘤发生中的意义，并确定Wnt/β-catenin信号在肿瘤发生中失控的新机制。对前列腺癌和其他肿瘤的新诊断标记物、治疗目标和方法的洞察是可望的。

DESCRIPTION (provided by applicant): Accumulated evidence has shown a significant role for the Wnt/?-catenin pathway in prostate development and tumorigenesis. Dysregulation of cytoplasmic and nuclear ?-catenin has been demonstrated to be a key event in tumorigenesis. Thus, the significance of ?-catenin in human tumors was corroborated by discoveries of mutations in both ?-catenin and the destruction complex components in tumor cells. More than 80% of colorectal cancers possess inactive mutations in the tumor suppressor, APC. Mutations in axin were also found in hepatocellular carcinomas. Moreover, point mutations within the four serine/threonine residues in the target sites of GSK32 were found in ?-catenin in a wide variety of human malignancies. Intriguingly, mutations in ?-catenin, APC, and other components of the destruction complex are very rare in prostate cancer samples. However, increased nuclear ?-catenin has been frequently observed in advanced prostate cancers during the disease progression. Therefore, other pathways/mechanisms may play a dominant role in the regulation of the Wnt/??-catenin signaling pathway during the course of prostate cancer initiation and progression. In the past, we identified that LAPSER1, also named LZTS2 (leucine zipper putative tumor suppressor 2), is a novel ?-catenin interacting protein. The human LZTS2 gene is located on chromosome 10q24.3. This region has been shown to be frequently lost in a variety of human tumors, including prostate cancer. Over- expression of LZTS2 protein affects the subcellular localization of ?-catenin, represses the transcriptional activity of ?-catenin, and inhibits cell growth. Intriguingly, a functional HIV Rev-like leucine rich, CRM1/exportin regulated nuclear export signal (NES) was identified within the C-terminus of LZTS2. Through this NES site, LZTS2 can enhance the nuclear export of ?-catenin and reduce the level of nuclear ?-catenin in cells. Using immunohistochemistry approaches, we further demonstrated that LZTS2 is expressed in the cytoplasm of luminal epithelial cells of prostate glands, and its expression is significantly reduced in human prostate tumor samples. These data elucidate an important role for LZTS2 as a novel regulator in Wnt/??-catenin-mediated transcription, cell growth, and tumorigenesis. Although a critical role for the Wnt/??-catenin signaling pathway has been established in prostate tumorigenesis, the precise pathways/mechanisms underlying the dysregulation of??-catenin in prostate cancer cells still remain unclear. Our recent findings that LZTS2 is a ?-catenin interacting protein and modulates the activity and cellular localization of ?-catenin point to LZTS2 as a novel regulator for the Wnt/??-catenin signaling pathway Therefore, we propose a series of experiments in this revised RO1 application to address our central hypothesis that LZTS2 negatively regulates the Wnt/??-catenin signaling pathway and its dysregulation will activate the Wnt/??-catenin signaling pathway and contribute to tumorigenesis. Three specific aims are proposed as follows: 1) characterizing the biological role of LZTS2 using knockout mouse models, 2) examining LZTS2 expression in human prostate cancers, and 3) investigating the dysregulation of Wnt/??-catenin signaling by LZTS2 in prostate tumorigenesis. The above specific aims address the significance of LZTS2 in tumorigenesis and identify the novel mechanisms for dysregulation of Wnt/??-catenin signaling in tumorigenesis. Insights into new diagnostic markers, therapeutic targets and approaches for prostate cancer and other tumors are expected.