title: Expression of high levels of human proteinase inhibitor 9 blocks both perforin/granzyme and Fas/Fas ligand-mediated cytotoxicity.
abstract: Proteinase inhibitor 9 (PI-9, SerpinB9) is the only known human intracellular granzyme B inhibitor. Whether expression of PI-9 is sufficient to block cytolysis induced by cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells remains controversial. To evaluate the roles of PI-9, we isolated and tested three lines of stably transfected HeLa cells expressing wild-type PI-9 and one line expressing an inactive mutant PI-9. Expressions of wild-type PI-9, but not the inactive mutant PI-9, inhibited cytolysis induced by human NK92 and NKL natural killer cells. Expression of high levels of PI-9 is therefore sufficient to protect human cells against NK cell-mediated cell death. Using two assays, we show that expressing wild-type PI-9, but not the inactive mutant PI-9, blocks Fas/Fas ligand (Fas/FasL)-mediated apoptosis. PI-9 expression has no effect on etoposide-induced apoptosis. HeLa cells exhibiting substantial resistance to Fas/FasL-mediated apoptosis contain 2- to 3-fold higher PI-9 levels than HCT116 human colon cancer cells and 2- to 3-fold lower PI-9 levels than MCF7/ERHA breast cancer cells, in which PI-9 is strongly induced by estrogens, and by tamoxifen. Expression of increasing levels of PI-9 in target cells may progressively inhibit immune surveillance by blocking NK and CTL-induced cytotoxicity through the perforin/granzyme pathway and then through the Fas/FasL pathway.
authors.affiliation: Department of Biochemistry, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Cunningham
authors.forename: Xinguo
authors.initials: X
authors.lastname: Jiang
authors.forename: David J
authors.initials: DJ
authors.lastname: Shapiro
mesh_terms: D017209:Apoptosis / Q000276:immunology; D002460:Cell Line; D003601:Cytotoxicity Tests, Immunologic; D053222:Fas Ligand Protein / Q000378:metabolism; D053804:Granzymes / Q000378:metabolism; D006367:HeLa Cells / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D054353:Perforin; D052899:Pore Forming Cytotoxic Proteins / Q000378:metabolism; D015843:Serpins / Q000378:metabolism*; D014162:Transfection; D019014:fas Receptor / Q000378:metabolism
chemical_list: C491901:FAS protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D052899:Pore Forming Cytotoxic Proteins; C102316:SERPINB9 protein, human; D015843:Serpins; D019014:fas Receptor; D054353:Perforin; D053804:Granzymes