Inhibition of Granzyme B by PI-9 protects prostate cancer cells from apoptosis

• Published in: The Prostate Vol. 72; no. 8; pp. 846 - 855
• Main Authors: Ray, Manisha, Hostetter, Daniel R., Loeb, Carly R.K., Simko, Jeffry, Craik, Charles S.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-06-2012; Wiley-Liss
• Subjects: Adenocarcinoma - metabolism; Adenocarcinoma - pathology; apoptosis; Apoptosis - physiology; Biological and medical sciences; Cell Line, Tumor; Disease Progression; Granzyme B; Granzymes - antagonists & inhibitors; Gynecology. Andrology. Obstetrics; Humans; immunosurveillance; Male; Male genital diseases; Medical sciences; Nephrology. Urinary tract diseases; PI-9; prostate cancer; Prostatic Neoplasms - metabolism; Prostatic Neoplasms - pathology; Serpins - metabolism; Tumors; Tumors of the urinary system; Up-Regulation; Urinary tract. Prostate gland; PI-9; Andrology; Nephrology; Urinary system disease; Prostate disease; Serine endopeptidases; Enzyme; Gynecology; Malignant tumor; immunosurveillance; Peptidases; Immunological surveillance; Granzyme B; Cell death; Hydrolases; Inhibitor; Inhibition; Male genital diseases; Prostate cancer; Tumor cell; Cancer; Apoptosis
• ISSN: 0270-4137; 1097-0045
• DOI: 10.1002/pros.21486

BACKGROUND
In order for tumors to grow and proliferate, they must avoid recognition by immune cells and subsequent death by apoptosis. Granzyme B (GrB), a protease located in natural killer cells, initiates apoptosis in target cells. Inhibition of GrB by PI‐9, its natural inhibitor, can prevent apoptosis. Here we investigate whether PI‐9 protects prostate cancer cells from apoptosis.
METHODS
The expression of PI‐9 was quantified by qPCR in several prostate cancer cell lines, and GrB activity was tested in each cell line. PI‐9 was overexpressed in LNCaP cells, which lack endogenous PI‐9. Apoptosis was induced by natural killer cells in LNCaP cells that either contained or lacked PI‐9, and the percent cell death was quantified. Lastly, PI‐9 levels were examined by qPCR and immunohistochemistry in prostate tumor tissue.
RESULTS
Prostate cancer cell lines that expressed PI‐9 could inhibit GrB. Overexpression of PI‐9 protected LNCaP cells from natural killer cell‐mediated apoptosis. Examination of the levels of PI‐9 in tissue from prostate tumors showed that PI‐9 could be upregulated in low grade tumors and stochastically dysregulated in high grade tumors. Additionally, PI‐9 was found consistently in high grade prostatic intraepithelial neoplasia and atrophic lesions.
CONCLUSIONS
These results indicate that overexpression of PI‐9 can protect prostate cancer cells from apoptosis, and this effect may occur in human prostate tumors. These findings imply that early prostatic inflammation may trigger this increase in PI‐9. This suggests that PI‐9 upregulation is needed early in tumor progression, before additional protective mechanisms are in place. Prostate 72:846–855, 2012. © 2011 Wiley Periodicals, Inc.