monorden and Lymphoma

Epstein-Barr virus (EBV) LMP1 is a major oncoprotein expressed in latent infection. It functions as a TNFR family member and constitutively activates cellular signals, such as NFκB, MAPK, JAK/STAT and AKT. We here screened small molecule inhibitors and isolated HSP90 inhibitors, Radicicol and 17-AAG, as candidates that suppress LMP1 expression and cell proliferation not only in EBV-positive SNK6 Natural Killer (NK) cell lymphoma cells, but also in B and T cells. Tumor formation in immuno-defficient NOD/Shi-scid/IL-2Rγ(null) (NOG) mice was also retarded. These results suggest that HSP90 inhibitors can be alternative treatments for patients with EBV-positive malignancies.

Topics: Animals; Antineoplastic Agents; B-Lymphocytes; Benzoquinones; Cell Proliferation; Epstein-Barr Virus Infections; Gene Expression Regulation; Herpesvirus 4, Human; HSP90 Heat-Shock Proteins; Humans; Immunocompromised Host; Killer Cells, Natural; Lactams, Macrocyclic; Lymphoma; Macrolides; Mice; Mice, Inbred NOD; Neoplasms, Experimental; Signal Transduction; Small Molecule Libraries; T-Lymphocytes; Tumor Burden; Viral Matrix Proteins

The molecular chaperone Hsp90 affects the function and fate of a number of signaling molecules. We have investigated the Hsp90 requirement for constitutive and inducible activity of the IkappaB kinase (IKK) complex and of NF-kappaB. Inhibition by the Hsp90 ATPase inhibitors, geldanamycin (GA) and radicicol (RC), revealed that Hsp90 controls IKKs at two levels, inducibility of enzymatic activity and biogenesis, which can be discriminated by short- and long-time GA incubation, respectively. Short-time inhibition of Hsp90 resulted in impaired IKK kinase activation by TNFalpha, IL-1beta or phorbolester PMA. Furthermore, GA inhibited constitutive activation of IKK and NF-kappaB in Hodgkin's lymphoma cells. Hsp90 function was also required for trans- and autophosphorylation of transfected IKKbeta. GA exposure for several hours resulted in a downmodulation of IKK complex alpha, beta and gamma subunits to various extent. Proteasome inhibition interfered with GA mediated IKK depletion and Hsp90 inhibition induced polyubiquitination of IKKalpha and beta during protein synthesis. In fact, GA blocked biogenesis of IKKalpha and IKKbeta but did not interfere with post-translational turnover. Together, these results define a dual requirement for Hsp90 as a regulator of NF-kappaB signaling by its general involvement in IKK activation and by its role in IKK homeostasis.

Topics: Animals; Benzoquinones; Cell Line; Cell Line, Tumor; COS Cells; Dose-Response Relationship, Drug; Enzyme Inhibitors; HeLa Cells; HSP90 Heat-Shock Proteins; Humans; I-kappa B Kinase; Inflammation; Interleukin-1; Lactams, Macrocyclic; Lactones; Lymphoma; Macrolides; Molecular Chaperones; NF-kappa B; Phosphorylation; Precipitin Tests; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Quinones; Signal Transduction; Tetradecanoylphorbol Acetate; Time Factors; Transfection; Tumor Necrosis Factor-alpha; Ubiquitin