Activation of NF-κB by the Human T Cell Leukemia Virus Type I Tax Oncoprotein Is Associated with Ubiquitin-dependent Relocalization of IκB Kinase

Abstract

Human T cell leukemia virus type 1 (HTLV-1) is the etiological agent of adult T cell leukemia. HTLV-1 encodes a trans-activating protein, Tax, which is largely responsible for the oncogenic properties of the virus. Tax promotes T cell transformation by deregulating the activity of various cellular factors, including the transcription factor NF-B. Tax activates the I B kinase (IKK) via physical interaction with the regulatory subunit, IKK␥, although it is unknown precisely how Tax activates the IKK complex. Here we show that Tax modulates the cellular localization of the IKK complex. The IKKs relocalize from a broad distribution in the cytoplasm to concentrated perinuclear "hot spots" in both HTLV-1-transformed lines and in Tax-expressing Jurkat cells. Relocalization of IKK is not observed with Tax mutants unable to activate NF-B, suggesting that only activated forms of IKK are relocalized. However, relocalization of IKK is strictly dependent on Tax expression because it does not occur in ATL cell lines that lack Tax expression or in Jurkat cells treated with phorbol 12-myristate 13-acetate and ionomycin. Furthermore, IKK␥ is required for redistribution because cells lacking IKK␥ were unable to relocalize IKK␣ upon expression of Tax. We also find that Tax ubiquitination likely regulates IKK relocalization because mutation of three critical lysine residues in Tax renders it unable to relocalize IKK and activate the canonical and noncanonical NF-B pathways. Finally, we have observed that the perinuclear IKK in Tax-expressing cells colocalizes with the Golgi, and disruption of Golgi with either nocodazole or brefeldin A leads to a redistribution of IKK to the cytoplasm. Together, these results demonstrate that Tax induces relocalization of the IKK complex in a ubiquitin-dependent manner, and dynamic changes in the subcellular localization of the IKK complex may be critical for Tax function.The human T cell leukemia virus type I (HTLV-1) 3 is associated with adult T cell leukemia (ATL), an aggressive malignancy of CD4 ϩ T cells, and a neuroinflammatory disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis (1). The HTLV-1 genome encodes a regulatory protein Tax in the pX region that plays a central role in HTLV-1-associated disease (2). Tax acts as a trans-activating protein that is critical for the expression of viral genes and also deregulates the expression of cellular genes. Tax regulates the expression of cellular genes by modulating signaling pathways such as NF-B, AP-1, CREB, and nuclear factor of activated T cells (3). Tax activation of NF-B is required for immortalization of T lymphocytes (4). Further, pharmacologic inhibition of NF-B leads to apoptosis of HTLV-1 transformed T cell lines and ATL cells (5).NF-B represents a family of transcription factors that regulate a wide variety of genes controlling cell survival, development, differentiation, and activation. NF-B family members include RelA (p65), c-Rel, RelB, p50, and p52, all of which contain a 300-amino acid Rel homology domain th...

Ubiquitylated Tax targets and binds the IKK signalosome at the centrosome

“…CREB activation is required for MTOC/Tax orientation to the cell-cell contact region, but not for Tax/MTOC association (Nejmeddine et al, 2005). That the Tax mutant M47 recruited IKK to the centrosome demonstrates that Tax-induced CREB Harhaj et al (2007), recently reported an association between perinuclear IKK and Tax that colocalize to the Golgi, we documented using complementary approaches that Tax/IKK complexes are associated with the centrosome rather than the Golgi apparatus. Our findings that Tax/IKK interaction occurs in the centrosome, unravel a new function for this cellular organelle.…”

An RNA Interference Screen Identifies the Deubiquitinase STAMBPL1 as a Critical Regulator of Human T-Cell Leukemia Virus Type 1 Tax Nuclear Export and NF-κB Activation

“…The regulation of Tax subcellular localization and trafficking to different compartments in the cell therefore impinges on the function of Tax (4,38). Recent studies have shown that posttranslational modifications of Tax regulate its function by governing its subcellular localization, stability, and protein-protein interactions (6,20,32). Tax is modified by a number of distinct posttranslational modifications, including ubiquitination, small ubiquitin (Ub)-like modifier sumoylation, phosphorylation, and acetylation (3,6,11,26,27,41), all of which regulate Tax function.…”

Suppression of HTLV-1 replication by Tax-mediated rerouting of the p13 viral protein to nuclear speckles

“…Tax has been shown to be both mono-and polyubiquitinated. 36,44,[52][53][54][55] Ubiquitination of Tax is important for both activation of the canonical and noncanonical NF-B pathway and localization to the cytoplasm. 44 Conversely, Tax is also sumoylated, which directs its nuclear localization and is important for both NF-B activation and HTLV-1 LTR activity.…”

“…36,53 In the cytoplasm, Tax also concentrates in perinuclear speckles that localize near the centrosome, the microtubule-organizing center, and the cis-Golgi. 54,56,57 Recently, K63-polyubiquitinated Tax was shown to recruit inhibitor B kinase complex to this perinuclear compartment, supporting a model in which Tax activates inhibitor B kinase in a centrosome-dependent manner. 56 However, preliminary data suggest that Tax itself may not need to be ubiquitinated to stabilize the p13 protein.…”