Persistent activation of NF-kappa B by the tax transforming protein involves chronic phosphorylation of IkappaB kinase subunits IKKbeta and IKKgamma.
The Tax transforming protein encoded by human T-cell leukemia virus type 1 (HTLV1) persistently activates transcription factor NF-kappaB and deregulates the expression of downstream genes that mediate cell cycle entry. We recently found that Tax binds to and chronically stimulates the catalytic function of IkappaB kinase (IKK), a cellular enzyme complex that phosphorylates and inactivates the IkappaB inhibitory subunit of NF-kappaB. We now demonstrate that the IKKbeta catalytic subunit and IKKgamma regulatory subunit of IKK are chronically phosphorylated in HTLV1-infected and Tax-transfected cells. Alanine substitutions at Ser-177 and Ser-181 in the T loop of IKKbeta protect both of these IKK subunits from Tax-directed phosphorylation and prevent the induction of IkappaB kinase activity. Each of these inhibitory effects is recapitulated in Tax transfectants expressing the bacterial protein YopJ, a potent in vivo agonist of T loop phosphorylation. Moreover, ectopically expressed forms of IKKbeta that contain glutamic acid substitutions at Ser-177 and Ser-181 have the capacity to phosphorylate a recombinant IKKgamma substrate in vitro. We conclude that Tax-induced phosphorylation of IKKbeta is required for IKKbeta activation, phosphoryl group transfer to IKKgamma, and acquisition of the deregulated IKK phenotype.
Carter
R S
RS
Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232-0295, USA.
Geyer
B C
BC
Xie
M
M
Acevedo-Suárez
C A
CA
Ballard
D W
DW
D001426:Bacterial Proteins / Q000378:metabolism; D020134:Catalytic Domain; D002453:Cell Cycle; D016356:Gene Products, tax / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051550:I-kappa B Kinase; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D001426:Bacterial Proteins; D016356:Gene Products, tax; D016328:NF-kappa B; D011994:Recombinant Proteins; C109227:YopP protein, Yersinia; D017346:Protein Serine-Threonine Kinases; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; C496565:IKBKE protein, human