KLK4 and prostate intraepithelial neoplasia: Of note, KLK4 protein is overexpressed in hyperplastic prostate epithelial cells, PIN lesions and malignant epithelium where it could be proteolytically activated by another protease expressed in prostate tissues such as KLK3, KLK11 or a member of MMP family (Bi et al., 2010; Yoon et al., 2007) and interact with adjacent stromal cells, suggesting that KLK4 secretion from these cells could be a key player in the early stromal differentiation to the CAF phenotype.