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Interleukin-15 Enhances Proteasomal Degradation of Bid in Normal Lymphocytes: Implications for Large Granular Lymphocyte Leukemias

¹ Laboratory of Experimental Immunology, Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute-Frederick, and SAIC Frederick; ² Laboratory of Protein Dynamics and Signaling, National Cancer Institute-Frederick, Frederick, Maryland; ³ The Burnham Institute for Medical Research, La Jolla, California; ⁴ Penn State Cancer Institute, College of Medicine, Penn State University, Hershey, Pennsylvania; and ⁵ Division of Molecular Diagnostics, Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania

Requests for reprints: Howard A. Young, Laboratory of Experimental Immunology, Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute-Frederick, and SAIC Frederick, 1050 Boyles Street, Building 560, Room 31-93, Frederick, MD 21702-1201. Phone: 301-846-5743; Fax: 301-846-1647; E-mail: younghow{at}mail.nih.gov.

Large granular lymphocyte (LGL) leukemia is a clonal proliferative disease of T and natural killer (NK) cells. Interleukin (IL)-15 is important for the development and progression of LGL leukemia and is a survival factor for normal NK and T memory cells. IL-15 alters expression of Bcl-2 family members, Bcl-2, Bcl-XL, Bim, Noxa, and Mcl-1; however, effects on Bid have not been shown. Using an adoptive transfer model, we show that NK cells from Bid-deficient mice survive longer than cells from wild-type control mice when transferred into IL-15-null mice. In normal human NK cells, IL-15 significantly reduces Bid accumulation. Decreases in Bid are not due to alterations in RNA accumulation but result from increased proteasomal degradation. IL-15 up-regulates the E3 ligase HDM2 and we find that HDM2 directly interacts with Bid. HDM2 suppression by short hairpin RNA increases Bid accumulation lending further support for HDM2 involvement in Bid degradation. In primary leukemic LGLs, Bid levels are low but are reversed with bortezomib treatment with subsequent increases in LGL apoptosis. Overall, these data provide a novel molecular mechanism for IL-15 control of Bid that potentially links this cytokine to leukemogenesis through targeted proteasome degradation of Bid and offers the possibility that proteasome inhibitors may aid in the treatment of LGL leukemia. [Cancer Res 2009;69(9):3986–94]

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