Journal of the National Cancer Institute Advance Access originally published online on March 10, 2009
JNCI Journal of the National Cancer Institute 2009 101(6):399-411; doi:10.1093/jnci/djn516
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© The Author 2009. Published by Oxford University Press.
ARTICLES |
Mechanism of Fas Signaling Regulation by Human Herpesvirus 8 K1 Oncoprotein
Affiliations of authors: Department of Lymphoma and Myeloma (ZB, SW, JFW, HM, FS), Department of Bioinformatics and Computational Biology (YJ) and Department of Immunology (FS), The University of Texas MD Anderson Cancer Center, Houston, TX; Department of Hemato-Oncology, National Health Insurance Corporation Ilsan Hospital, Goyang Si, Gyeonggi-Do, South Korea (HM)
Correspondence to: Felipe Samaniego, MD, Department of Lymphoma and Myeloma, The University of Texas MD Anderson Cancer Center, 7455 Fannin St, Houston, TX 77054 (e-mail: fsamaniego{at}mdanderson.org).
Background: Herpesvirus 8 (HHV-8) oncoprotein K1 is linked to lymphoproliferation and suppression of apoptosis mediated by the Fas death receptor. Expression of K1 in transgenic mice induces accumulation of lymphoid tissue cells and lymphoma.
Methods: To examine how K1 and Fas interact to suppress apoptosis, K1–Fas binding was studied in human embryonic kidney (HEK) and lymphoma (BJAB) cells that expressed wild-type K1 or a K1 Ig domain deletion mutant and were treated with Fas ligand (FasL) or an agonistic Fas antibody, using immunoprecipitation and Western blot analysis. Cleavage of caspase-3 and apoptosis was compared in liver samples from mice that were transfected with empty vector vs with plasmids expressing wild-type K1 or a K1 Ig deletion mutant and treated with agonistic Fas antibody for 7 hours. These studies used immunohistochemical staining and terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling assay. All statistical tests were two-sided.
Results: Immunoprecipitation and Western blot analysis of transfected HEK and BJAB cells revealed that wild-type K1 but not Ig-deleted K1 binds to Fas and prevents Fas activation by FasL or by an agonistic Fas antibody. More mice that were transfected with wild-type K1 (7 of 10) than mice transfected with empty vector (3 of 13) or the K1 Ig deletion mutant (0 of 6) survived treatment with the agonistic Fas antibody. Compared with vector-transfected mice, livers of wild-type K1-transfected mice contained fewer cells in which caspase-3 was cleaved (87.6% vs 58.0%, difference = 29.6%, 95% confidence interval [CI] = 19.2% to 40.0%; P = .003) and fewer apoptotic cells (83.7% vs 34.2%, difference = 49.5%, 95% CI = 39.8% to 59.2%; P = .003).
Conclusions: K1 blocks Fas signaling by directly binding to Fas through the Ig-like domain of K1 and preventing binding of FasL. The relative resistance of cancer cells to Fas-mediated apoptosis may be due to the inhibition of Fas by Ig domain–containing proteins.
| CONTEXT AND CAVEATS Prior knowledge Herpesvirus 8 oncoprotein K1 has a role in Fas death receptor–mediated proliferation of cells in the lymph nodes and suppression of cell death, and its expression in transgenic mice leads to lymphoma. Study design K1–Fas binding and cell death were assayed after treatment with Fas ligand (FasL) or agonistic Fas antibody in cell lines that expressed wild-type K1 or an Ig domain deletion mutant. Survival of mice transfected with wild-type K1 or an Ig domain deletion mutant after treatment with agonistic Fas antibody. Contributions Wild-type K1 but not the Ig domain deletion mutant binds to Fas and inhibits its activation by FasL or agonistic Fas antibody. Wild-type K1 but not the mutant increased the survival of mice treated with agonistic Fas antibody. Implications The Ig domain of K1 is essential to Fas binding and inhibition. Limitations Whether these interactions occur in vivo in cells that are infected with the virus is unknown. The protein interactions observed could have been nonspecific interactions that were driven by overexpression of the K1 protein. From the Editors
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Manuscript received April 24, 2008; revised December 2, 2008; accepted December 29, 2008.
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J Natl Cancer Inst 2009 101: 361.