Proteasome-mediated Degradation of Hematopoietic Progenitor Kinase 1 in Pancreati

描述（由申请人提供）：HPK1，也称为MAP4K1，是一种与哺乳动物ste20相关的丝氨酸/苏氨酸激酶，已被证明可以抑制Erk并激活NF？B和JNK通路(1)。虽然许多研究已经确定了HPK1在造血细胞增殖、分化和凋亡中的作用，但HPK1在恶性肿瘤的恶性转化、增殖和侵袭中的作用尚未得到研究。最近，我们发现HPK1蛋白在正常胰管中表达，但在95%的胰管癌（PDC）样本中缺失。HPK1蛋白的缺失与低级别胰腺上皮内瘤变（PanIN）向侵袭性PDC的进展密切相关。更重要的是，恢复PDC细胞中野生型HPK1蛋白的表达导致细胞周期阻滞和生长抑制，这部分是由于p21和p27的上调(2)。因此，我们的数据首次表明，HPK1可能作为一种新的肿瘤抑制因子，其缺失在PDC的发展中起着关键作用。此外，我们还证明PDC中HPK1的丢失是由于蛋白酶体介导的蛋白质降解，而不是在mRNA水平上，并且PDC中HPK1蛋白的丢失需要HPK1激酶活性(2)。我们对HPK1在体内的调控知之甚少。最近，我们发现Fbw8是E3连接酶，负责PDC中蛋白酶体介导的HPK1蛋白降解。在本研究中，我们将研究Fbw8靶向HPK1蛋白降解的新分子机制以及Fbw8在胰腺癌中的致癌功能。这些研究的完成不仅将揭示HPK1在胰腺癌中调控的新分子途径，也将为胰腺癌治疗找到新的靶点。我们有以下两个特定目的：特定目的1：研究泛素E3连接酶Fbw8在蛋白酶体介导的胰腺癌HPK1蛋白降解中的机制。特异性目的2：探讨fbw8介导的HPK1降解在胰腺癌肿瘤生长和转移中的作用。

DESCRIPTION (provided by applicant): HPK1, also named MAP4K1, is a mammalian Ste20-related serine/threonine kinase and has been shown to inhibit Erk and activate NF?B and JNK pathways (1). While a number of studies have identified the role of HPK1 in proliferation, differentiation and apoptosis in hematopoietic cells, the role of HPK1 in malignant transformation, proliferation, and invasion in malignancies has not been examined. Recently, we demonstrated that HPK1 protein is expressed in normal pancreatic ducts, but is lost in >95% of pancreatic ductal carcinoma (PDC) samples. The loss of HPK1 protein is strongly associated with the progression from low-grade pancreatic intraepithelial neoplasia (PanIN) to invasive PDC. More importantly, restoring wild type HPK1 protein expression in PDC cells resulted in cell cycle arrest and growth inhibition, which is due in part to up- regulation of p21 and p27 (2). Thus, our data showed, for the first time, that HPK1 may function as a novel tumor suppressor and its loss plays a critical role in the development of PDC. In addition, we have also demonstrated that loss of HPK1 in PDC is due to proteasome-mediated protein degradation, but not at the mRNA levels and that HPK1 kinase activity is required for the loss of HPK1 protein in PDC (2). Little is known about the regulation of HPK1 in vivo. Recently, we have identified Fbw8 as the E3 ligase that is responsible for proteasome-mediated degradation of HPK1 protein in PDC. In this proposal, we will examine the novel molecular mechanisms by which Fbw8 targets HPK1 protein for degradation and the oncogenic functions of Fbw8 in pancreatic cancer. Accomplishment of the proposed studies will not only reveal the novel molecular pathways of HPK1 regulation in pancreatic cancer, but also identify new targets for pancreatic cancer treatment. We have the following two Specific Aims: Specific Aim 1: To examine the mechanism of ubiquitin E3 ligase, Fbw8, in proteasome-mediated degradation of HPK1 protein in pancreatic cancer. Specific Aim 2: To examine the function of Fbw8-mediated HPK1 degradation in tumor growth and metastasis of pancreatic cancer. PUBLIC HEALTH RELEVANCE: Proteasome-mediated Degradation of Hematopoietic Progenitor Kinase 1 in Pancreatic Cancer We recently demonstrated that HPK1 function as a novel tumor suppressor and that proteasome-mediated degradation of HPK1 protein is strongly associated with the progression from low-grade pancreatic intraepithelial neoplasia (PanIN) to invasive pancreatic cancer. In this proposal, we will examine the detailed molecular mechanisms of proteasome-mediated degradation of HPK1 protein and to examine the possible oncogenic functions of the newly identified ubiquitin-E3 ligase, Fbw8, that is responsible for HPK1 degradation in pancreatic cancer. Accomplishment of the proposed studies will reveal novel pathways of HPK1 regulation in pancreatic cancer and identify novel targets for pancreatic cancer treatment.