Expression of a kallikrein-like protein in prostatic intraepithelial neoplasia in ventral prostate of the noble rat.

Background: In an effort to identify biomarker(s) for prostatic cancer (PCa), we analyzed the changes of secretory proteins in the ventral prostate (VP) of Noble rats at early stages of carcinogenesis.

Methods: Ventral prostates were removed from both control (n = 36) and experimental (n = 88) rats implanted with a known ratio of testosterone (T) and 17beta-estradiol (E(2)). Tissue sections were stained by hematoxylin and eosin (H&E) for pathological screening, and secretions were collected for SDS-PAGE analysis followed by N-terminal microsequencing, antiserum production, Western blot, and immunohistochemical study.

Results: Pathologically, low-grade prostatic intraepithelial neoplasia (LGPIN) and high-grade PIN (HGPIN) were observed in ducts or alveoli after 3 and 5 months of T + E(2) treatment, respectively. The results of SDS-PAGE showed an elevated expression of 18-kDa protein (p18) in secretions of VP with HGPIN or cancerous lesions. Analysis of p18 by N-terminal sequencing showed a high score of homology to rat glandular kallikrein. To characterize the expression pattern of the protein in tissue samples, an antiserum was raised against the N-terminus of the p18. The monospecificity of the antiserum against p18 was confirmed by Western blot analysis. Immunohistochemical study showed that in ducts or alveoli of normal and LGPIN samples, a mild positive staining for p18 was observed in secretions. However, the reactivity was intense not only in luminal secretions but also in some luminal secretory cells in HGPIN and cancer cells as well.

Conclusions: The high expression of p18 in connection with neoplastic transformation of cells strongly suggests that the potential application of this protein as a marker for early detection of PCa should be further investigated.