Department of Pharmacy, School of Health Sciences, University of Patras, Rion-Patras, Greece.
The Keenan Research Center in the Li Ka Shing Knowledge Institute, Department of Laboratory Medicine, St. Michael's Hospital, Toronto, Canada.
Mol Oncol. 2019 Nov;13(11):2329-2343. doi: 10.1002/1878-0261.12493. Epub 2019 Sep 30.
Kallikrein-related peptidase 6 (KLK6) is a serine protease normally expressed in mammary tissue and aberrantly regulated in breast cancer. At physiological levels, KLK6 functions as a suppressor of breast cancer, while its aberrant overexpression (> 50-fold higher than normal) is characteristic of a subset of breast cancers and has been linked to accelerated growth of primary breast tumors in severe combined immunodeficiency mice (Pampalakis et al. Cancer Res 2009, 69, 3779). Here, we investigated the molecular mechanisms underlying the concentration-dependent functions of KLK6 by comparing MDA-MB-231 stable transfectants expressing increasing levels of KLK6 in in vitro and in vivo tumorigenicity assays (soft agar, xenograft growth, tail vein metastasis). Quantitative proteomics was applied to identify proteins that are altered upon re-expression of KLK6 in MDA-MB-231 at normal or constitutive levels. Overexpression of KLK6 is associated with increased metastatic ability of breast cancer cells into lungs, increased expression of certain S100 proteins (S100A4, S100A11) and keratins (KRT), and downregulation of the apoptosis-related proteases CASP7 and CASP8, and RABs. On the other hand, KLK6 re-expression at physiological levels leads to inhibition of lung metastases associated with suppression of S100 proteins (S100A4, S100A10, S100A13, S100A16) and induced CASP7 and CASP8 expression. As this is the first report that KLK6 expression is associated with S100 proteins, caspases, RABs, and KRTs, we validated this finding in clinical datasets. By integrating proteomics and microarray data from breast cancer patients, we generated two composite scores, KLK6 + S100B-S100A7 and KLK6 + S100B-S100A14-S100A16, to predict long-term survival of breast cancer patients. We present previously unknown pathways implicating KLK6 in breast cancer. The findings promise to aid our understanding of the functional roles of KLK6 in breast cancer and may yield new biomarkers for the cancer types in which KLK6 is known to be aberrantly upregulated.
激肽释放酶相关肽 6（KLK6）是一种丝氨酸蛋白酶，通常在乳腺组织中表达，并在乳腺癌中异常调节。在生理水平下，KLK6 作为乳腺癌的抑制剂发挥作用，而其异常过表达（比正常水平高 50 倍以上）是乳腺癌亚群的特征，并与严重联合免疫缺陷小鼠原发性乳腺肿瘤的加速生长有关（Pampalakis 等人，Cancer Res 2009, 69, 3779）。在这里，我们通过比较 MDA-MB-231 稳定转染细胞在体外和体内肿瘤发生测定（软琼脂、异种移植生长、尾静脉转移）中表达 KLK6 水平逐渐升高的稳定转染细胞，研究了 KLK6 浓度依赖性功能的分子机制。应用定量蛋白质组学方法鉴定了在 MDA-MB-231 中重新表达 KLK6 时发生改变的蛋白质，其表达水平为正常或组成型水平。KLK6 的过表达与乳腺癌细胞向肺部转移能力的增加、某些 S100 蛋白（S100A4、S100A11）和角蛋白（KRT）的表达增加以及凋亡相关蛋白酶 CASP7 和 CASP8 的下调有关，另一方面，KLK6 在生理水平上的重新表达与 S100 蛋白（S100A4、S100A10、S100A13、S100A16）的抑制以及诱导 CASP7 和 CASP8 的表达有关，与肺转移的抑制有关。由于这是 KLK6 表达与 S100 蛋白、半胱天冬酶、RAB 和 KRT 相关的首次报道，我们在临床数据集上验证了这一发现。通过整合乳腺癌患者的蛋白质组学和微阵列数据，我们生成了两个综合评分 KLK6+S100B-S100A7 和 KLK6+S100B-S100A14-S100A16，以预测乳腺癌患者的长期生存。我们提出了以前未知的途径，涉及 KLK6 在乳腺癌中的作用。这些发现有望帮助我们理解 KLK6 在乳腺癌中的功能作用，并可能为 KLK6 异常上调的癌症类型提供新的生物标志物。
