Novel Role(s) of Nrf2 in the Growth of Post-Transplantation Cancer

 描述(申请人提供)：晚期肾细胞癌(RCC)的治疗选择有限。有趣的是，肾癌也是接受免疫抑制治疗的器官移植患者的关键问题，特别是钙调神经磷酸酶抑制剂(CNI)。因此，移植受者的癌症加速速率可以作为一个独特的模型来理解肾肿瘤生长的机制(S)。我们发现，在CNI诱导的肾癌中，Ras-Raf通路高度激活，促进抗氧化和细胞保护分子血红素加氧酶-1(HO-1)的过度表达。HO-1介导肾癌细胞的快速生长和存活，并可导致对化疗的抵抗。HO-1基因敲除后，肾癌治疗常用药物的细胞凋亡作用明显增强。我们最近发现，转录因子Nrf2在Ras-Raf通路的诱导下在肾癌中高度激活，并介导HO-1的过度表达。肾癌中Ras-Raf通路高激活的可能机制之一(S)是通过上游受体酪氨酸激酶(RTK)进行信号传递。RTK c-Met在肾癌中高表达；在初步研究中，我们观察到c-Met的诱导激活了RAS通路，并诱导了Nrf2/HO-1。正如所讨论的，肾癌是实体器官移植患者中最常见的癌症之一。癌基因，包括ras，在移植后期间被激活。我们已经证明，尽管CNI是非常好的延长移植物存活的免疫抑制剂，但它们可以促进移植后癌症的快速进展；CNI诱导的肿瘤与Ras/Raf-1/Nrf2激活、HO-1过度表达和血管生成有关。有趣的是，我们还观察到CNI治疗可以促进c-Met的磷酸化增加，因此c-Met可能是CNI诱导和Ras-Nrf2介导的肾肿瘤生长的关键分子。总之，Nrf2有很大的潜力被认为是肾癌的一个新的治疗靶点。我们推测，靶向c-Met-Ras-Nrf2通路和抑制HO-1将减弱肾癌的生长、血管生成和进展(对CNI诱导的移植后癌具有重要意义)，并将显著促进化疗药物的肿瘤杀伤力。为此，我们将研究：1)CNI和c-Met诱导途径(S)在调节RAS介导的肾癌细胞NRF2激活/稳定中的作用(AIM-1)；2)NRF2在调控CNI和c-MET诱导的肾癌细胞生长中的作用(S)；3)c-Met/Raf-1和NRF2在小鼠器官移植模型中诱导肾癌生长的作用；以及评估NRF2和HO-1在移植和非移植患者肾肿瘤组织中的表达(AIM-3)。总之，我们的研究应该确定c-Met-Ras-Nrf2-HO-1促肿瘤通路是肾癌的一个新的治疗靶点，特别是对CNI诱导的移植后癌症特别重要。这应该会导致目前肾癌治疗方法的范式转变。

 DESCRIPTION (provided by applicant): There are limited treatment options for advanced renal cell carcinoma (RCC). Interestingly, kidney cancer is also a critical problem in organ transplant patients receiving immunosuppressive therapy, particularly with calcineurin inhibitors (CNIs). Thus, the accelerated rate of cancer in transplant recipients can serve as a unique model to understand the mechanism(s) of renal tumor growth. We discovered that in CNI-induced renal cancer, the Ras-Raf pathway is highly activated to promote over-expression of the anti-oxidant and cytoprotective molecule heme oxygenase-1 (HO-1). HO-1 mediates a rapid growth and survival of renal cancer cells, and it can lead to resistance against chemotherapeutic treatments. The apoptotic effects of commonly used drugs for renal cancer treatment were markedly enhanced upon HO-1 knockdown. We recently identified that the transcription factor Nrf2 is highly activated in RCC through the induction of Ras-Raf pathway, and it mediates HO-1 over-expression. One of the possible mechanism(s) for hyper activation of the Ras-Raf pathway in RCC is due to the signaling through upstream receptor tyrosine kinases (RTKs). The RTK c-MET is over-expressed in RCC; and in preliminary studies, we observed that the induction of c-MET activates the Ras pathway and induces Nrf2/HO-1. As discussed, kidney cancer is one of the most common cancers in patients having solid organ transplantation. Oncogenes, including ras, become activated during post-transplantation period. We have demonstrated that although CNIs are very good immunosuppressive agents to prolong allograft survival, they can promote a rapid progression of post-transplantation cancer; and CNI-induced tumors were associated with Ras/Raf-1/Nrf2 activation, HO-1 over-expression and angiogenesis. Interestingly, we also observed that the CNI treatment can promote an increased phosphorylation of c-MET; and thus c-MET can possibly be a critical molecule for CNI-induced and Ras-Nrf2-mediated renal tumor growth. Together, Nrf2 has a great potential to be considered as a novel therapeutic target in RCC. We hypothesize that targeting the c-MET-Ras-Nrf2 pathway and the inhibition of HO-1 will attenuate the growth, angiogenesis and progression of renal cancer (with importance to CNI-induced post-transplantation cancer), and it will significantly promote the tumor killing efficienc of chemotherapeutic agents. In our specific aims, we will study: 1) roles of CNI- and c- MET-induced pathway(s) in the regulation of Ras-mediated Nrf2 activation/stabilization in renal cancer cells (Aim-1); 2) role(s) of Nrf2 in regulating CNI- and c-MET-induced growth of renal cancer cells (Aim-2); and 3) roles of c-MET/Raf-1 and Nrf2 in CNI-induced renal cancer growth after organ transplantation in murine model; and to evaluate the expression of Nrf2 and HO-1 in renal tumor tissues from transplant and non-transplant patients (Aim-3). Together, our studies should identify the c-MET-Ras-Nrf2-HO-1 tumor-promoting pathway as a new and novel therapeutic target in RCC, with particular importance to CNI-induced post-transplantation cancer. It should lead to a paradigm shift for current therapies in renal cancer.