Urokinase-type plasminogen activator (uPA) has been shown to activate matrix metalloproteinase-2 (MMP-2) that leads to the migration and invasion of breast cancer cells. Overexpressed uPA and MMP-2 are regarded as signs of malignant tumors in clinical practice. Therefore, real-time monitoring of the sequential activation of these two signal molecules may have important implications for the evaluation of the invasive potential and tumor progression of breast cancer. However, due to the complicated intracellular environment, visualizing the dynamic changes of protein expression levels in living cells with a noninvasive method is still a great challenge. Here, a novel gold–selenium (Au–Se) fluorescent nanoprobe with excellent selectivity and strong anti-interference capability was designed for the simultaneous in situ imaging of uPA and MMP-2 and real-time monitoring of their changes in living cells. The imaging results demonstrated that the nanoprobe achieved a better prevention of glutathione interference compared to the conventional Au–S nanoprobe, thus it could be applied to actually reflect the expression level of uPA and MMP-2 in different breast cancer cells. Furthermore, the Au–Se nanoprobe could visually present the activation process of the two signal molecules, which play a dual role of insuring the invasiveness evaluation of breast cancer cells. Overall, our work offers a visual biomarker detection method for the judgment of the degree of breast cancer malignancy, and also provides an effective strategy to investigate the relationships among signal molecules of other signaling pathways in the future.

中文翻译：

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Au-Se纳米探针，用于通过对uPA和MMP-2的顺序激活进行成像来评估乳腺癌细胞的侵袭潜能。

尿激酶型纤溶酶原激活剂（uPA）已显示可激活基质金属蛋白酶2（MMP-2），从而导致乳腺癌细胞迁移和侵袭。在临床实践中，过表达的uPA和MMP-2被认为是恶性肿瘤的体征。因此，实时监测这两个信号分子的顺序激活可能对评估乳腺癌的浸润潜能和肿瘤进展具有重要意义。然而，由于复杂的细胞内环境，用无创方法可视化活细胞中蛋白质表达水平的动态变化仍然是巨大的挑战。在此，设计了一种新颖的金-硒（Au-Se）荧光纳米探针，该探针具有出色的选择性和强大的抗干扰能力，可同时进行原位检测。uPA和MMP-2的成像以及实时监测它们在活细胞中的变化。成像结果表明，与常规的Au–S纳米探针相比，纳米探针能更好地预防谷胱甘肽干扰，因此可用于实际反映uPA和MMP-2在不同乳腺癌细胞中的表达水平。此外，Au-Se纳米探针可以在视觉上呈现两个信号分子的激活过程，这在确保乳腺癌细胞的浸润性评估中起着双重作用。总体而言，我们的工作提供了一种可视化的生物标志物检测方法来判断乳腺癌的恶性程度，并且还为将来研究其他信号通路的信号分子之间的关系提供了有效的策略。