ABSTRACT: Background: Tissue kallikrein-related peptidases 4, 5, 6 and 7 (KLK4-7) strongly increase the malignancy of ovarian cancer cells. By further deciphering the downstream effectors of KLK4-7, we aimed at finding new potential prognostic biomarkers and treatment targets for ovarian cancer patients. KLK4-7-transfected and vector-control OVMZ-6 (OV-KLK4-7 and OV-VC) ovarian cancer cells were established to select differentially regulated factors. Methods: Three independent approaches, PCR arrays, genome-wide microarray and proteome analyses, were pursued leading to the identification of ten candidates (MSN, KRT19, COL5A2, COL1A2, BMP5, F10, KRT7, JUNB, BMP4, MMP1). Differential gene expression in OV-KLK4-7 versus OV-VC cells was validated by qPCR. To determine differential protein expression, Western blot analyses, immunofluorescence and immunohistochemistry were applied for four candidates (MSN, KRT19, KRT7, JUNB) in both cell lines and tumor xenografts. Results: These experiments demonstrated that KLK4-7 distinctly regulate expression of MSN, KRT19, KRT7 and JUNB on the mRNA and protein levels in ovarian cancer cells and tissues. Protein expression of the top upregulated effectors, MSN and KRT19, was investigated by immunohistochemistry in a cohort of patients (n=66) afflicted with high-grade serous ovarian cancer and related to the immuno-expression levels of KLK4-7. Significant positive associations were found for KRT19/KLK4 (P=0.010), KRT19/KLK5 (P=0.030) and MSN/KLK7 (P=0.001); KRT19 and MSN immuno-expression showed a trend towards significance with KLK6. Conclusions: These findings imply that KLK4-7 exert key modulatory effects on other cancer-related genes and proteins in ovarian cancer. The key downstream effectors of KLK4-7, MSN and KRT19, may represent important therapeutic targets associated with serous ovarian cancer.
