The Role of N-cadherin in Tumor Progresion

描述(申请人提供)：癌症转移是一个复杂的多步骤过程，包括癌细胞从原发肿瘤中分离，向内扩散，在血流中存活，向外渗出，以及在远处器官中建立新的病灶。细胞-细胞和细胞-基质黏附的变化伴随着从良性肿瘤向侵袭性恶性肿瘤的转变以及随后的肿瘤细胞的转移扩散。钙粘附素是一类在正常组织中以组织特异性方式表达的细胞黏附分子家族。E-钙粘附素负责维持上皮细胞的正常组织，在转移性肿瘤中经常下调。相反，N-钙粘附素的从头表达常见于上皮性肿瘤。N-钙粘附素改变了乳腺癌细胞在培养过程中的细胞行为，使它们更具运动性和侵袭性。钙粘蛋白亚型转换(E-钙粘蛋白为N-钙粘蛋白)是肿瘤进展的标志，但人们对N-钙粘蛋白在体内如何影响肿瘤细胞行为知之甚少。我们培育了一只N-钙粘素条件性基因敲除(CKO)小鼠(传统的N-钙粘蛋白KO是胚胎致死的)，为在基因定义的动物模型中研究肿瘤进展和转移中对N-钙粘素的需求提供了机会。将N-钙粘蛋白CKO模型与一种新的胰腺导管癌变模型相结合，该模型将突变的K-ras靶向胰腺前体细胞。该动物模型概括了胰腺癌患者从胰腺上皮内瘤变(Panin)到胰腺导管腺癌(PDA)的发展过程。我们描述了体内证据表明，N-钙粘附素的缺失会导致肿瘤发生的增加。基于这些初步数据，我们假设N-钙粘素介导的黏附/信号的丢失通过改变肌动蛋白细胞骨架来解除细胞接触对细胞生长的抑制。这一假设将被以下相互关联的特定目标所追求：(1)表征在缺乏N-钙粘附素的情况下Panin向PDA的进展；(2)评估N-钙粘附素丢失对细胞骨架调节因子RhoA的影响；(3)确定焦点粘连在N-钙粘附素介导的接触性抑制细胞生长的调节中的作用。这项探索性的R21拨款将确定在胰腺癌中从E-钙粘素到N-钙粘素的基因转换的基因阻断的后果。了解胰腺癌进展的分子机制可能会为新的抗肿瘤治疗的发展提供洞察力。公共卫生相关性：我们出人意料的发现，N-钙粘蛋白的丢失导致K-RasG12D；N-钙粘蛋白/FLOX；Pdx1-CRE小鼠Panin发育增加，这为揭示调控肿瘤生长的新分子机制提供了一个切入点。此外，鉴于N-钙粘素拮抗剂ADH-1目前处于IIb期临床试验(http://www.adherex.com).)，更好地了解N-钙粘素在体内的功能是当务之急了解胰腺癌进展的分子机制可能会为新的抗肿瘤治疗的发展提供洞察力。

DESCRIPTION (provided by applicant): Abstract Cancer metastasis is a complex multistep process, involving the detachment of cancer cells from the primary tumor, intravasation, survival in the bloodstream, extravasation, and establishment of new foci in distant organs. Changes in cell-cell and cell-matrix adhesion accompany the transition from benign tumors to invasive, malignant cancer and the subsequent metastatic dissemination of tumor cells. Cadherins are a family of cell adhesion molecules expressed in a tissue specific manner in normal tissues. E-cadherin is responsible for maintaining the normal organization of the epithelia and is often downregulated in metastatic tumors. In contrast, de novo expression of N-cadherin is often observed in tumors of epithelial origin. N-cadherin alters the cellular behavior of breast cancer cells in culture rendering them more motile and invasive. Cadherin subtype switching (E-cadherin to N- cadherin) is a hallmark of tumor progression, yet it is poorly understood how N-cadherin affects tumor cell behavior in vivo. We generated an N-cadherin conditional knockout (CKO) mouse (conventional N-cadherin KO is embryonic lethal), providing an opportunity to examine the requirement for N- cadherin in tumor progression and metastasis in a genetically defined animal model. The N-cadherin CKO model was combined with a novel pancreatic ductal carcinogenesis model that targets mutant K-ras to pancreatic progenitor cells. This animal model recapitulates the progression of pancreatic intraepithelial neoplasia (PanIN) to pancreatic ductal adenocarcinoma (PDA) observed in human patients with pancreatic cancer. We describe in vivo evidence that loss of N-cadherin results in increased tumorigenesis. Based on these preliminary data, we hypothesize that loss of N-cadherin- mediated adhesion/signaling relieves cell contact inhibition of cell growth by altering the actin cytoskeleton. This hypothesis will be pursued by the following interrelated Specific Aims: (1) To characterize the progression of PanIN to PDA in the absence of N-cadherin; (2) To evaluate the effects of loss of N-cadherin on the cytoskeletal regulator, RhoA; (3) To determine the role of focal adhesions in the regulation of N-cadherin-mediated contact inhibition of cell growth. This exploratory R21 grant will determine the consequences of genetically blocking the switch from E-cadherin to N- cadherin in pancreatic cancer. Understanding the molecular mechanisms underlying the progression of pancreatic cancer may provide insight for the development of novel antineoplastic therapies. PUBLIC HEALTH RELEVANCE: Our unexpected finding that loss of N-cadherin leads to increased PanIN development in K-rasG12D; N-cadflox/flox; Pdx1-Cre mice provides an entry point to uncover novel molecular mechanisms regulating tumor growth. Furthermore, a better understanding of N-cadherin function in vivo is imperative given that the N-cadherin antagonist, ADH-1, is now in Phase IIb clinical trial (http://www.adherex.com). Understanding the molecular mechanisms underlying the progression of pancreatic cancer may provide insight for the development of novel antineoplastic therapies.