Kallikrein-related peptidase 6 (KLK6) expression differentiates tumor subtypes and predicts clinical outcome in breast cancer patients
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Novel molecular markers that address the heterogeneity of breast cancer (BC) and provide meaningful prognostic information for BC patients are needed. Kallikrein-related peptidase 6 (KLK6) is aberrantly expressed and functionally implicated in BC and, like other members of the KLK family, may prove a useful molecular tool for clinical management. Our objective was to assess, for the first time, the clinical relevance of KLK6 mRNA expression in BC. Total RNA was isolated from 165 breast tumors, as well as 100 adjacent non-cancerous tumor specimens. After cDNA synthesis, and following quality control, quantitative real-time PCR for KLK6 expression analysis took place. Receiver operating characteristic curves were constructed in order to assess the ability of KLK6 mRNA expression levels to differentiate between molecular BC subtypes. Survival analyses, using DFS as endpoint, were performed at the univariate and multivariate levels. Publicly available BC databases and online survival analysis tools were used to validate our findings. A significant downregulation of KLK6 mRNA expression was observed in BC tissue sections compared to the non-cancerous component (P < 0.001). The expression of KLK6 is positively associated with tumor grade (P = 0.038) and is overexpressed in TNBC and HER2-positive tumors (P < 0.001). Aberrant KLK6 expression predicts the clinical outcome of BC patients in terms of DFS, independently of currently used prognostic markers (HR = 7.11, 95% CI = 1.19–42.45). The differential expression of KLK6 and its association with unfavorable outcome in BC patients was validated via in silico analyses. Although an independent external cohort is necessary to confirm our findings, we proved for the first time that KLK6 can provide independent prognostic information for BC patients.
KeywordsKLK6 Kallikreins KLKs Serine proteases Biological tumor marker Prognostic biomarker
Area under the curve
Distant metastasis-free survival
Epidermal growth factor receptor
Epithelial to mesenchymal transition
Human epidermal growth factor receptor 2
Hypoxanthine phosphoribosyltransferase 1
Receiver operating characteristic
- RQ units
Relative quantification units
Spearman correlation coefficient
Robust single sample predictor classification
Quantitative real-time PCR
Single sample predictors
Triple-negative breast cancer
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
- 6.Schmitt M, Dorn J, Kiechle M, Diamandis EP, Luo L. Clinical relevance of kallikrein-related peptidases in breast cancer. Berlin, Boston: DE GRUYTER; 2012. p. 111–44.Google Scholar
- 8.Pampalakis G, Prosnikli E, Agalioti T, Vlahou A, Zoumpourlis V, Sotiropoulou G. A tumor-protective role for human kallikrein-related peptidase 6 in breast cancer mediated by inhibition of epithelial-to-mesenchymal transition. Cancer Res. 2009;69(9):3779–87. https://doi.org/10.1158/0008-5472.CAN-08-1976.CrossRefPubMedGoogle Scholar
- 15.Michel N, Heuze-Vourc’h N, Lavergne E, et al. Growth and survival of lung cancer cells: regulation by kallikrein-related peptidase 6 via activation of proteinase-activated receptor 2 and the epidermal growth factor receptor. Biol Chem. 2014;395(9):1015–25. https://doi.org/10.1515/hsz-2014-0124.CrossRefPubMedGoogle Scholar
- 17.Michaelidou K, Ardavanis A, Scorilas A. Clinical relevance of the deregulated kallikrein-related peptidase 8 mRNA expression in breast cancer: a novel independent indicator of disease-free survival. Breast Cancer Res Treat. 2015;152(2):323–36. https://doi.org/10.1007/s10549-015-3470-8.CrossRefPubMedGoogle Scholar
- 19.Wolff AC, Hammond ME, Hicks DG, et al. Recommendations for human epidermal growth factor receptor 2 testing in breast cancer: American Society of Clinical Oncology/College of American Pathologists clinical practice guideline update. J Clin Oncol. 2013;31(31):3997–4013. https://doi.org/10.1200/JCO.2013.50.9984.CrossRefPubMedGoogle Scholar
- 20.Goldhirsch A, Wood WC, Coates AS, et al. Strategies for subtypes–dealing with the diversity of breast cancer: highlights of the St. Gallen International Expert Consensus on the Primary Therapy of Early Breast Cancer 2011. Ann Oncol. 2011;22(8):1736–47. https://doi.org/10.1093/annonc/mdr304.CrossRefPubMedPubMedCentralGoogle Scholar
- 28.Gyorffy B, Lanczky A, Eklund AC, et al. An online survival analysis tool to rapidly assess the effect of 22,277 genes on breast cancer prognosis using microarray data of 1,809 patients. Breast Cancer Res Treat. 2010;123(3):725–31. https://doi.org/10.1007/s10549-009-0674-9.CrossRefPubMedGoogle Scholar
- 35.Mange A, Dimitrakopoulos L, Soosaipillai A, Coopman P, Diamandis EP, Solassol J. An integrated cell line-based discovery strategy identified follistatin and kallikrein 6 as serum biomarker candidates of breast carcinoma. J Proteom. 2016;142:114–21. https://doi.org/10.1016/j.jprot.2016.04.050.CrossRefGoogle Scholar
- 36.Schrader CH, Kolb M, Zaoui K, et al. Kallikrein-related peptidase 6 regulates epithelial-to-mesenchymal transition and serves as prognostic biomarker for head and neck squamous cell carcinoma patients. Mol Cancer. 2015;14:107. https://doi.org/10.1186/s12943-015-0381-6.CrossRefPubMedPubMedCentralGoogle Scholar
- 39.Kim TW, Lee SJ, Kim JT, et al. Kallikrein-related peptidase 6 induces chemotherapeutic resistance by attenuating auranofin-induced cell death through activation of autophagy in gastric cancer. Oncotarget. 2016;7(51):85332–48. https://doi.org/10.18632/oncotarget.13352.PubMedPubMedCentralGoogle Scholar