Mechanisms of Overexpressed TrkB in Inducing Pancreatic Cancer Metastasis

描述(申请人提供)：胰腺癌是美国成年人癌症死亡的第四大原因，在过去的25年里，5年存活率一直保持在1-3%。确诊时，大约80%的胰腺癌患者患有局部晚期或转移性疾病，中位生存期不到6个月。即使当I期或II期胰腺癌明显局限于胰腺并经手术切除时，70%的患者在手术后2年内仍会发生肝转移。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。虽然胰腺癌的基因图谱正在形成，但启动和调节其主要临床特征局部侵袭性生长、转移和化疗耐药的特定基因改变的作用仍未解决。胰腺癌细胞发生侵袭和转移的潜在机制仍有待阐明。识别标志性基因和分子改变在胰腺肿瘤发生和转移中的功能将为设计新的治疗方法提供分子基础。因此，这项研究的长期目标是利用携带胰腺癌标志性基因改变的小鼠模型研究胰腺转移的分子基础，并研究这些基因改变导致的表型。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之一，在转移性胰腺癌细胞株Colo357L3.6pl中高表达，而在非转移亲代细胞株Colo357FG中不表达。TrkBT1的过表达与胰腺癌肝转移的发生有关。在其他转移性胰腺癌细胞系中，TrkBT1也是TrkB的主要过表达形式。通过其shRNA诱导的失巢凋亡来击倒TrkBT1。TrkBT1在非转移性Colo357FG细胞中过表达可诱导软琼脂集落形成和裸鼠肝转移，但TrkBT1突变体如何诱导胰腺癌转移仍有待进一步研究。TrkBT1变异体通过激活RhoA在胰腺癌转移中起关键作用的假说将得到进一步验证。其特异性目的是确定GDI1、RhoA以及GDI1和RhoA的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。更好地了解基因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。靶向胰腺癌中的特定突变和信号通路可能是治疗肿瘤转移的新的治疗干预措施之一。

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.