Targeted inhibition of calcineurin signaling blocks calcium-dependent reactivation of Kaposi sarcoma-associated herpesvirus

Kaposi sarcoma-associated herpesvirus (KSHV) is associated with KS, primary effusion lymphoma (PEL), and multicentric Castleman disease. Reactivation of KSHV in latently infected cells and subsequent plasma viremia occur befo re the development of KS. Intracellular signaling pathways involved in KSHV reactivation were studied. In latently infected PEL cells (BCBL-1), KSHV r eactivation in single cells was determined by quantitative flow cytometry. Viral particle production was determined by electron microscope analyses an d detection of minor capsid protein in culture supernatants. Agents that mo bilized Intracellular calcium (ionomycin, thapsigargin) induced expression of KSHV lytic cycle-associated proteins and led to increased virus producti on. Calcium-mediated virus reactivation was blocked by specific inhibitors of calcineurin-dependent signal transduction (cyclosporine, FK506). Similar ly, calcium-mediated virus reactivation in KSHV-infected dermal microvascul ar endothelial cells was blocked by cyclosporine, Furthermore, retroviral t ransduction with plasmid DNA encoding VIVIT, a peptide specifically blockin g calcineurin-NFAT interactions, inhibited calcium-de-pendent KSHV reactiva tion. By contrast, chemical induction of lytic-phase infection by the phorb ol ester 12-O-tetradecanoyl-phorbol-13-acetate was blocked by protein kinas e C inhibitors, but not by calcineurin inhibitors. In summary, calcineurin- dependent signal transduction, an important signaling cascade in vivo, indu ces calcium-dependent KSHV replication, providing a possible target for the design of antiherpesvirus strategies in KSHV-infected patients. (Blood, 20 01;97: 2374-2380) (C) 2001 by The American Society of Hematology.