Mechanisms of Overexpressed TrkB in Inducing Pancreatic Cancer Metastasis

描述（由申请人提供）：胰腺癌是美国成人癌症死亡的第四大原因，在过去的25年里，胰腺癌的5年生存率一直保持在1-3%。在诊断时，大约80%的胰腺癌患者患有治疗耐药的局部晚期或转移性疾病，中位生存期小于6个月。即使I期或II期胰腺癌明显局限于胰腺并手术切除，70%的患者仍在手术后2年内发生肝转移。目前对转移性胰腺癌的治疗大多无效。因此，胰腺癌是癌症研究中最大的挑战之一。尽管胰腺癌的遗传谱正在出现，但特异性基因改变在启动和介导其局部侵袭性生长、转移和化疗耐药性等主要临床特征中的作用仍未得到解决。胰腺癌细胞侵袭性和转移性的潜在机制仍有待阐明。识别胰腺肿瘤发生和转移中特征遗传和分子改变的功能将为设计新的治疗方法提供分子基础。因此，本研究的长期目标是利用携带该疾病中发现的标志性遗传改变的小鼠模型来研究胰腺转移的分子基础，并研究这些遗传改变诱导的表型。我们最近的研究结果表明，原肌球蛋白相关激酶BT1 （TrkBT1）是蛋白酪氨酸激酶受体家族的成员，在转移性胰腺癌细胞系col357l3.6 pl中过表达，但在非转移性亲本细胞系col357fg中不表达。TrkBT1的过表达与人胰腺腺癌肝转移的发生有关。TrkBT1也是其他转移性胰腺癌细胞系中主要的TrkB过表达形式。TrkBT1被其shRNA敲低所诱发的病症。非转移性col357fg细胞中TrkBT1过表达诱导软琼脂集落形成和裸鼠肝转移，但缺乏激酶结构域的TrkBT1变异体如何诱导胰腺癌转移仍有待进一步研究。TrkBT1变异通过激活RhoA在胰腺癌转移中发挥关键作用的假设将进一步得到验证。我们的具体目的是确定GDI1、RhoA以及GDI1和RhoA shRNA的表达是否会改变胰腺癌细胞的转移潜能，并阐明TrkBT1诱导肝转移的机制。更好地了解遗传改变诱导转移表型的机制将为制定有效的胰腺癌治疗策略提供基础。针对胰腺癌的特异性突变和信号通路可能是治疗癌症转移的新干预措施之一。

DESCRIPTION (provided by applicant): Pancreatic cancer is the fourth leading cause of cancer mortality in adults in the United States, with a 5- year survival rate that has remained at 1-3% for the past 25 years. At diagnosis, approximately 80% of pancreatic cancer patients have therapy-resistant locally advanced or metastatic disease with a median survival of less than 6 months. Even when stage I or II pancreatic cancer is apparently localized to the pancreas and surgically removed, 70% of those patients still develop liver metastases within 2 years after surgery. Current treatments of metastatic pancreatic cancer are largely ineffective. Pancreatic cancer thus poses one of the greatest challenges in cancer research. Although a genetic profile for pancreatic caner is emerging, the role of specific genetic alterations that initiate and mediate its cardinal clinical features of locally aggressive growth, metastasis, and chemotherapy resistance, remains unresolved. The underlying mechanisms, by which pancreatic cancer cells become invasive and metastatic, remain to be elucidated. Identification of the functions of the signature genetic and molecular alterations in pancreatic tumorigenesis and metastasis will provide a molecular basis for designing novel therapeutic approaches. Therefore, the long-term objective of the proposed research is to study the molecular basis of pancreatic metastasis using mouse models, which carry the signature genetic alterations found in this disease, and study the phenotypes induced by these genetic alterations. Our recent findings show that tropomyosin-related kinase BT1 (TrkBT1), which is a member of the protein tyrosine kinase receptor family, is overexpressed in metastatic pancreatic cancer cell line, Colo357L3.6pl, but not in the nonmetastatic parental cell line, Colo357FG. The overexpression of TrkBT1 has been related to occurrence of liver metastasis in human pancreatic adenocarcinoma. TrkBT1 was also the predominant overexpressed form of TrkB in other metastatic pancreatic cancer cell lines. Knock down of TrkBT1 by its shRNA induced anoikis. Overexpression of TrkBT1 in nonmetastatic Colo357FG cells induced colony formation in soft agar and liver metastasis in nude mice, but how the TrkBT1 variant, which lacks kinase-domain, induces pancreatic cancer metastasis remain to be further established. The hypothesis, the TrkBT1 variant play a key role in pancreatic cancer metastasis by activation of RhoA will be further tested. The specific aims are to determine whether the expression of GDI1, RhoA, and shRNA for GDI1 and RhoA will alter the metastatic potential of the pancreatic cancer cells, and to elucidate the mechanism by which the TrkBT1 induced the liver metastasis. A better understanding of the mechanisms of genetic alterations in induction of metastatic phenotypes will provide a basis for developing effective treatment strategies for pancreatic cancer. Targeting specific mutations and signaling pathways in pancreatic cancer may be one of the novel therapeutic interventions to treat cancer metastasis. PUBLIC HEALTH RELEVANCE: Pancreatic cancer remains an unsolved health problem in the United States and throughout the world. Only through basic and translational research aimed at understanding molecular basis of pancreatic cancer and identifying novel targets for designing therapeutic approaches will the outcome change for the over 42,470 people in the United States who develop this disease each year. The proposed study will fill in the gaps in our understanding of the molecular mechanisms of human pancreatic cancer metastasis by studying the novel signaling pathways mediated by TrkBT1 overexpression.