The human T-cell leukemia virus type-1 Tax protein regulates the activity of the IkappaB kinase complex

• Published in: The Journal of biological chemistry Vol. 274; no. 48; pp. 34417 - 34424
• Main Authors: Li, X H, Murphy, K M, Palka, K T, Surabhi, R M, Gaynor, R B
• Format: Journal Article
• Language: English
• Published: United States 26.11.1999
• Subjects: Animals; Blotting, Western; Cadmium - pharmacology; Cell Extracts - chemistry; Chromatography - methods; COS Cells; Cyclin-Dependent Kinase-Activating Kinase; Cyclin-Dependent Kinases; Electrophoresis, Polyacrylamide Gel; Enzyme Activation - drug effects; Gene Expression; Gene Products, tax - genetics; Gene Products, tax - physiology; Human T-lymphotropic virus 1; Humans; I-kappa B Kinase; I-kappa B Proteins - metabolism; Jurkat Cells; MAP Kinase Kinase Kinase 1; MAP Kinase Kinase Kinases - metabolism; NF-kappa B - metabolism; NF-kappaB-Inducing Kinase; Protein Serine-Threonine Kinases - chemistry; Protein Serine-Threonine Kinases - metabolism; T-Lymphocytes - enzymology; T-Lymphocytes - virology; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha - pharmacology
• ISSN: 0021-9258; 1083-351X

Two cytokine-inducible kinases, IKKalpha and IKKbeta, are components of a 700-kDa kinase complex that specifically phosphorylates IkappaB. Phosphorylation of IkappaB by IKK leads to its ubiquitination and subsequent degradation, resulting in the nuclear translocation of NF-kappaB. The oncogenic protein Tax, encoded by human T-cell leukemia virus type-1 (HTLV-1), stimulates IKK activity to result in constitutive nuclear levels of NF-kappaB. In an attempt to gain insights into the mechanism by which Tax mediates constitutive activation of the NF-kappaB pathway, we analyzed the chromatographic distribution of IKK proteins using cellular extracts prepared from three T lymphocytes either lacking or containing Tax. IKK kinase activity and the distribution of proteins in the IKK complex were characterized. In extracts prepared from cells containing Tax, the activity of both IKKalpha and IKKbeta present in the 700-kDa IKK complex were increased. Surprisingly, cell lines expressing Tax also contained an additional peak of IKKbeta, but not IKKalpha activity, that migrated at 300 kDa rather than at 700 kDa. We noted that extracts containing Tax had extremely low levels of IkappaBbeta, but not IkappaBalpha, and contained predominantly a truncated form of the MAP3K MEKK1. These results suggest that Tax may target several components of the NF-kappaB pathway leading to constitutive activation of this important regulator of cellular gene expression.