Regulation of Immune Surveillance and Apoptosis by Proteinase Inhibitor 9
REGULATION OF IMMUNE SURVEILLANCE AND APOPTOSIS BY PROTEINASE INHIBITOR 9
Collaborators: Professors William Helferich and David Kranz (UIUC), and Elaine Alarid (Univ of Wisconsin)
Alumni: Dr. Xinguo Jiang, Dr. Thomas Cunningham, Dr. Adam Krieg, Dr. Sasha Krieg
When antigens are properly displayed on the surface of a transformed or infected cell, they engage receptors on the immune cells, Cytotoxic T Lymphocytes (CTLs) and Natural Killer (NK) cells. This activates both the caspase 8 and caspase-10 dependent Fas Ligand pathway, which usually plays a secondary role in immune cell mediated death, and most important, induces the release of particles containing granzyme proteases. After entry into target cells, granzyme B cleaves the precursor forms of several caspases and induces apoptosis. In humans, Proteinase inhibitor 9 or PI-9 is the only intracellular inhibitor of granzyme B. We showed that estrogen induction of high levels of PI-9 inhibits caspases 8 and 10 and inhibits apoptosis mediated by the tumor necrosis factor (TNF), TRAIL, and Fas/Fas ligand death receptor apoptosis pathways (Krieg AJ, et al., (2004) J Biol Chem, 279:5025-5034; Cuningham TD, et al., (2007) Cellular Immunology, 245:32-41). The actions of PI-9 are summarized in the figure.
Estrogen induction of PI-9 inhibits immunosurveillance
Estrogen induces PI-9 and protects breast cancer cells from immune surveillance and apoptosis (Jiang X, et al., (2006) Endocrinology, 147:1419-1426). Since there was some controversy over the role of PI-9, we used RNAi knockdown to look at the requirement for PI-9 in estrogen protection of MCF-7 breast cancer cells against immune-cell mediated apoptosis. Our data established that estrogen’s ability to inhibit NK cell mediated apoptosis stems from its ability to induce PI-9 (Jiang X, et al., (2007) Oncogene, 26:4106-4114). While these data showed that induction of PI-9 was necessary to inhibit NK cell mediated apoptosis, they did not show whether or not expression of PI-9 was sufficient to block apoptosis. To test this, we produced stably transfected cell lines expressing PI-9 under the control of a regulated promoter. Expression of wild-type PI-9 was sufficient to protect cells against apoptosis induced by NK cells and by Fas ligand. Expression of a mutant PI-9 unable to inhibit proteases did not block apoptosis (Cuningham TD, et al., (2007) Cellular Immunology, 245:32-41). Our data show that in marked contrast to many actions of estrogens that involve complex changes in the level and activity of large numbers of proteins and pathways, estrogen induction of a single protein, proteinase inhibitor 9 (PI-9), is both necessary and sufficient to enable breast cancer cells to evade killing by human immune cells. Inducing PI-9 and thereby enabling breast cancer cells to evade killing by immune system cells, likely represent a new way that estrogens contribute to the growth and spread of breast cancer.
Genistein potently induces PI-9 and blocks immunosurveillance
We next looked at the effects of the soy isoflavone genistein on immunosurveillance. In the U.S., genistein is widely consumed in supplements as a “natural estrogen.” Genistein is usually considered to be a very weak estrogen on ERα. Very low, physiologically relevant nanomolar concentrations of genistein induce PI-9 and block killing of breast cancer cells by human immune cells. The PI-9 system provides a striking example of how an unusual DNA binding site can contribute to greatly enhanced transcription by an otherwise weak ER ligand. Moderate levels of dietary soy and a common soy supplement induce PI-9 in MCF-7 cells and in a mouse xenograft model and elicit levels of circulating genistein that are similar to those seen in humans using soy supplements or consuming soy rich diets (Jiang X, et al., (2008) Endocrinology, 149:5366-5373)
Cunningham TD, Jiang X and Shapiro, DJ (2007) Expression of high levels of human proteinase inhibitor 9 blocks both perforin/granzyme and Fas/Fas ligand-mediated cytotoxicity. Cellular Immunology, 245:32-41.
Jiang X, Ellison SJ, Alarid, ET and Shapiro DJ (2007) Interplay between the levels of estrogen and estrogen receptor controls the level of the granzyme inhibitor, proteinase inhibitor 9 and susceptibility to immune surveillance by natural killer cells. Oncogene, 26: 4106-4114.
Jiang X, Patterson NM, Ling Y, Xie J, Helferich WG and Shapiro DJ (2008) Low concentrations of the soy phytoestrogen genistein induce proteinase inhibitor 9 and block killing of breast cancer cells by immune cells. Endocrinology, 149, 5366-5373.
Jiang X, Shapiro DJ. (2014) The immune system and inflammation in breast cancer. Mol Cell Endocrinol., 382(1): 673-82. (Recommended by Faculty of 1000 Prime)