Kaposi’s Sarcoma Associated Herpesvirus Encoded Viral FLICE Inhibitory Protein K13 Activates NF-κB Pathway Independent of TRAF6, TAK1 and LUBAC

• DOI: 10.1371/journal.pone.0036601
• Publication Date: 2012-05-08T20:51:45Z
• Authors: Hittu Matta; Ramakrishnan Gopa...; Ciaren Graham; Bhairavi Tolani; Akshat Khanna; Han Yi; Yulan Suo; Preet M. Chaudhary
• Keywords: 0301 basic medicine; Science; 610; Dermatitis; KSHV; Jurkat Cells; Mice; Viral Proteins; 03 medical and health sciences; NEMO; TRAF; Animals; Humans; Sarcoma, Kaposi; Inflammation; K13; Mice, Knockout; TNF Receptor-Associated Factor 6; Ubiquitin; C700 - Molecular biology; Q; R; Intracellular Signaling Peptides and Proteins; NF-kappa B; C540 - Virology; biophysics & biochemistry; Fibroblasts; Embryo, Mammalian; MAP Kinase Kinase Kinases; I-kappa B Kinase; 3. Good health; Multiprotein Complexes; Chronic Disease; Herpesvirus 8, Human; Medicine; Research Article

Kaposi's sarcoma associated herpesvirus encoded viral FLICE inhibitory protein (vFLIP) K13 activates the NF-κB pathway by binding to the NEMO/IKKγ subunit of the IκB kinase (IKK) complex. However, it has remained enigmatic how K13-NEMO interaction results in the activation of the IKK complex. Recent studies have implicated TRAF6, TAK1 and linear ubiquitin chains assembled by a linear ubiquitin chain assembly complex (LUBAC) consisting of HOIL-1, HOIP and SHARPIN in IKK activation by proinflammatory cytokines.Here we demonstrate that K13-induced NF-κB DNA binding and transcriptional activities are not impaired in cells derived from mice with targeted disruption of TRAF6, TAK1 and HOIL-1 genes and in cells derived from mice with chronic proliferative dermatitis (cpdm), which have mutation in the Sharpin gene (Sharpin(cpdm/cpdm)). Furthermore, reconstitution of NEMO-deficient murine embryonic fibroblast cells with NEMO mutants that are incapable of binding to linear ubiquitin chains supported K13-induced NF-κB activity. K13-induced NF-κB activity was not blocked by CYLD, a deubiquitylating enzyme that can cleave linear and Lys63-linked ubiquitin chains. On the other hand, NEMO was required for interaction of K13 with IKK1/IKKα and IKK2/IKKβ, which resulted in their activation by "T Loop" phosphorylation.Our results demonstrate that K13 activates the NF-κB pathway by binding to NEMO which results in the recruitment of IKK1/IKKα and IKK2/IKKβ and their subsequent activation by phosphorylation. Thus, K13 activates NF-κB via a mechanism distinct from that utilized by inflammatory cytokines. These results have important implications for the development of therapeutic agents targeting K13-induced NF-κB for the treatment of KSHV-associated malignancies.