Novel regulatory role for Kaposi's sarcoma-associated herpesvirus-encoded vFLIP in chemosensitization to bleomycin.
Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) is associated with malignancy. KSHV-derived vFLIP is structurally related to cellular FLIP and binds to NEMO/IκB kinase (IKKγ) to activate NF-κB signaling. NF-κB activation is postulated to confer chemoresistance to various anticancer drugs. However, here we showed that vFLIP expression uniquely sensitized HEK293 cells to bleomycin and its derivatives. Chemosensitization to bleomycin by vFLIP accompanied accumulation of γ-H2AX and G2/M-arrest of cells, while bleomycin-induced DNA damage checkpoints, such as phosphorylation of Chk2 and foci formation of Rad51, were similarly detected in both parental and vFLIP-expressing cells, suggesting that primary DNA damage was not affected by vFLIP. Paradoxically, while NF-κB activity was little affected by bleomycin treatment, vFLIP-stimulated NF-κB activity was suppressed by it. Additionally, cAMP-response element (CRE)- and p53-dependent transcriptional reporter activity was negatively regulated by vFLIP in the presence of bleomycin. Interestingly, a negative regulatory phosphatase essential for G2 checkpoint recovery and for dephosphorylation of γ-H2AX, Wip1/PPM1D, whose gene promoter is regulated by p53, CRE and NF-κB, was selectively downregulated in vFLIP-expressing cells after bleomycin treatment. These results suggest that vFLIP-mediated transcriptional regulation such as Wip1/PPM1D repression is involved in chemosensitization to bleomycin.
Division of Chemotherapy, Faculty of Pharmacy, Keio University, 1-5-30 Shibakoen, Minato-ku, Tokyo 105-8512, Japan.
Yuri
Y
Masuda
Kohji
K
Noguchi
Hatsune
H
Segawa
Noritaka
N
Tanaka
Kazuhiro
K
Katayama
Junko
J
Mitsuhashi
Yoshikazu
Y
Sugimoto
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D001761:Bleomycin / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D004249:DNA Damage; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects / Q000235:genetics; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D010749:Phosphoprotein Phosphatases / Q000235:genetics; D000071636:Protein Phosphatase 2C; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
D000903:Antibiotics, Antineoplastic; C468783:H2AX protein, human; D006657:Histones; D014764:Viral Proteins; C481275:viral FLIP protein, Human herpesvirus 8; D001761:Bleomycin; C000607458:PPM1D protein, human; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C