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Original Article

^a Department of Immunology, Wenner-Gren Institute, University of Stockholm, S-10691 Stockholm, Sweden
^b Immunopathology Laboratory, Institute for Oncology-Pathology, the Karolinska Institute and Hospital, S-17177 Stockholm, Sweden
^c Institute of Immunology, National Hospital, University of Oslo, N-0172 Oslo, Norway
Dept. of Immunology, the Wenner-Gren Institute, University of Stockholm, S-10691 Stockholm, Sweden.46-8-15-41-6346-8-16-41-78

alf.grandien{at}imun.su.se

Death receptor–mediated apoptosis can be modulated by several antiapoptotic proteins, such as the FLICE (FADD [Fas-associated death domain]-like IL-1β–converting enzyme)-inhibitory proteins (FLIPs). The FLIP family includes both cellular and viral members. The Kaposi's sarcoma–associated herpesvirus protein (KSHV)-FLIP is expressed by human herpesvirus 8 (HHV-8), which is associated with malignancies such as Kaposi's sarcoma and certain lymphomas. In this paper, we demonstrate that KSHV-FLIP protects cells from Fas-mediated apoptosis by inhibiting caspase activation and permits clonal growth in the presence of death stimuli in vitro. Furthermore, we show that KSHV-FLIP can act as a tumor progression factor by promoting tumor establishment and growth in vivo. When injected into immunocompetent recipient mouse strains, murine B lymphoma cells (A20) transduced with KSHV-FLIP rapidly develop into aggressive tumors showing a high rate of survival and growth. The tumor-progressive activity of KSHV-FLIP is mediated by prevention of death receptor–induced apoptosis triggered by conventional T cells. Consequently, inhibitors of death receptor signaling can be regarded as a new class of tumor progression factors, and HHV-8–associated tumors may represent naturally occurring examples of the tumorigenic effect of such inhibitors.

Key Words: apoptosis • Fas receptor • antiapoptotic proteins • herpesvirus • lymphoma

M. Djerbi and V. Screpanti contributed equally to this work.

© 1999 The Rockefeller University Press

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