The Regulation of UPA and UPAR in Human Carcinoma Cells

描述（由申请人提供）：在各种恶性肿瘤中检测到尿激酶纤溶酶原激活物（uPA）及其受体（uPAR）的过表达。体内外研究表明uPA/uPAR在肿瘤的进展和转移中起重要作用。为了确定侵袭性癌细胞中高uPA/uPAR表达的机制，我们先前表明：1）内源性p38 MAPK活性在侵袭性癌细胞中升高，并且是高uPA/uPAR表达所必需的; 2）p38 MAPK通过促进uPA mRNA稳定性来维持高uPA表达。然而，p38 MAPK如何稳定uPA mRNA在浸润性癌细胞中仍不清楚。在我们的初步研究中，我们鉴定了一种RNA结合蛋白SECp 43，它不仅与p38 a MAPK特异性相互作用，而且在体外还作为p38 a MAPK的直接底物。在p38 MAPK抑制的条件下，过表达SECp 43使uPA mRNA不稳定，而沉默SECp 43表达延长uPA mRNA的半衰期，表明SECp 43和p38 a MAPK在调节uPA mRNA稳定性方面功能相关。在进一步的研究中，我们发现SECp 43与uPA mRNA在体内的稳定性相互作用，并且uPA mRNA中SECp 43相互作用所需的区域含有富含AU的元件（ARE）基序。有趣的是，我们还发现p38 MAPK活性和uPA表达升高的细胞表现出弱的SECp 43/uPA mRNA相互作用，反之亦然。这些结果表明，p38 a MAPK可能通过阻碍SECp 43介导uPA mRNA降解的能力来稳定uPA mRNA。本研究旨在利用我们以前的工作1）研究p38 a MAPK如何调节SECp 43介导的uPA mRNA降解; 2）确定SECp 43介导的uPA mRNA周转的机制; 3）确定非p38 a磷酸化的SECp 43如何影响肿瘤细胞的生长和转移。该研究将增加我们对p38 MAPK介导的mRNA稳定性和浸润性癌细胞中uPA/uPAR表达升高的机制的理解。此外，获得对SECp 43在抑制uPA表达中的新作用的进一步理解可能导致开发抑制肿瘤生长和转移的新治疗方法。

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.