Expression of protein C inhibitor (PCI) in benign and malignant prostatic tissues.

Protein C inhibitor (PCI) occurs at high concentration in seminal plasma, and inhibits human glandular kallikrein-2 and, less readily, prostate-specific antigen. Previous studies have localized PCI in the male genital tract. Here we have performed a detailed investigation of PCI expression in the prostatic tissues, metastases, and cell lines. Immunohistochemistry, in situ hybridization, and Western blotting were used to study prostatic tissues, metastases, and PC-3, DU-145, and LNCaP cells. PCI was immunolocalized in tissue microarray spots with BPH epithelium (detection rate 100%), PIN lesions (100%), tumors (96%), metastases (88%), and in all cell lines. ISH and WB supported the findings. PCI is widely expressed in benign prostatic epithelium, and may act as a local regulator of enzymatic activity in seminal fluid, of importance for normal sperm function. Lack of PCI expression in a subpopulation of high-grade tumor cells in combination with maintained protease expression may facilitate invasive growth patterns.