The Regulation of UPA and UPAR in Human Carcinoma Cells

描述(申请人提供)：尿激酶型纤溶酶原激活物(UPA)及其受体(UPAR)在多种恶性肿瘤中过表达。体外和体内研究均表明，uPA/uPAR在肿瘤的进展和转移中起重要作用。为了明确侵袭性癌细胞中uPA/uPAR高表达的机制，我们以前曾证明：1)侵袭性癌细胞内源性p38MAPK活性升高，这是高表达uPA/uPAR所必需的；2)p38MAPK通过促进uPA mRNA的稳定来维持uPA的高表达。然而，p38MAPK如何稳定侵袭性癌细胞中的uPA mRNA仍不清楚。在我们的初步研究中，我们发现了一个RNA结合蛋白SECp43，它不仅可以与P38A MAPK特异地相互作用，而且在体外也可以作为P38A MAPK的直接底物。在p38 MAPK抑制条件下，SECp43的过表达破坏了uPA mRNA的稳定性，而SECp43的表达沉默则延长了uPA mRNA的半衰期，提示SECp43和P38A MAPK在调节uPA mRNA稳定性方面存在功能联系。在进一步的研究中，我们发现SECp43在体内与uPA mRNA的稳定性相互作用，并且SECp43相互作用所需的uPA mRNA区域含有富含AU的元件(ARE)基序。有趣的是，我们还发现，p38MAPK活性和uPA表达升高的细胞表现出较差的SECp43/uPA mRNA相互作用，反之亦然。这些结果提示，P38A MAPK可能通过阻断SECp43‘S介导uPA基因的降解而稳定uPA基因的表达。这项建议旨在利用我们之前的工作：1)研究P38A MAPK如何调控SECp43介导的uPA mRNA衰退；2)确定SECp43介导的uPA mRNA周转所涉及的机制；以及3)确定非P38A可磷酸化的SECp43如何影响肿瘤细胞的生长和转移。这项拟议的研究将加深我们对p38MAPK介导的mRNA稳定以及侵袭性癌细胞中uPA/uPAR表达上调的机制的理解。此外，进一步了解SECp43在抑制uPA表达中的新作用可能会导致开发一种新的治疗方法来抑制肿瘤的生长和转移。

DESCRIPTION (provided by applicant): The overexpression of urokinase plasminogen activator (uPA) and its receptor (uPAR) is detected in various malignancies. Both in vitro and in vivo studies demonstrate that uPA/uPAR play an important role in tumor progression and metastasis. To define the mechanism responsible for high uPA/uPAR expression in invasive cancer cells, we previously showed that 1) the endogenous p38 MAPK activity is elevated in invasive cancer cells and is required for high uPA/uPAR expression; and 2) p38 MAPK maintains high uPA expression by promoting uPA mRNA stability. However, how p38 MAPK stabilizes uPA mRNA in invasive cancer cells remains unclear. In our preliminary studies, we identified an RNA-binding protein SECp43 that not only specifically interacts with p38a MAPK but also serves as a direct substrate of p38a MAPK in vitro. Overexpression of SECp43 destabilizes uPA mRNA while silencing SECp43 expression prolongs uPA mRNA half-life in p38 MAPK-inhibited condition, suggesting that SECp43 and p38a MAPK are functionally linked in regulating uPA mRNA stability. In further study, we found that SECp43 interacts with uPA mRNA stability in vivo and the region in uPA mRNA required for SECp43 interaction contains AU-rich element (ARE) motifs. Interestingly, we also found that cells with elevated p38 MAPK activity and uPA expression exhibit poor SECp43/uPA mRNA interaction and vice versa. These results suggest that p38a MAPK may stabilize uPA mRNA by impeding SECp43's ability to mediate uPA mRNA decay. This proposal seeks to capitalize on our previous work to 1) investigate how p38a MAPK regulates SECp43-mediated uPA mRNA decay; 2) determine the mechanisms involved in SECp43-mediated uPA mRNA turnover; and 3) determine how non-p38a-phosphorylable SECp43 affects tumor cell growth and metastasis. The proposed study should increase our understanding on p38 MAPK-mediated mRNA stabilization and mechanisms involved in elevated uPA/uPAR expression in invasive cancer cells. Also, gaining further understanding of the novel role of SECp43 in repressing uPA expression may lead to the development of a novel therapeutic approach to suppress tumor growth and metastasis.