title: Inhibition of Granzyme B by PI-9 protects prostate cancer cells from apoptosis.
abstract: 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.
authors.affiliation: Graduate Group in Biochemistry and Molecular Biology, University of California, San Francisco, California 94158-2517, USA.
authors.forename: Manisha
authors.initials: M
authors.lastname: Ray
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Hostetter
authors.forename: Carly R K
authors.initials: CR
authors.lastname: Loeb
authors.forename: Jeffry
authors.initials: J
authors.lastname: Simko
authors.forename: Charles S
authors.initials: CS
authors.lastname: Craik
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D017209:Apoptosis / Q000502:physiology; D045744:Cell Line, Tumor; D018450:Disease Progression; D053804:Granzymes / Q000037:antagonists & inhibitors*; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D015843:Serpins / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: C102316:SERPINB9 protein, human; D015843:Serpins; D053804:Granzymes