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Molecular characterization of the protein-protein interaction between HTLV-1 Tax and GSK-3ß




Wang, Guoliang, author
Nyborg, Jennifer, advisor
Bamburg, James R., committee member
Quackenbush, Sandra L., committee member
Laybourn, Paul J., committee member

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The human T-cell leukemia virus type 1 (HTLV-1) encodes a viral oncoprotein termed Tax, which plays a major role in transforming HTLV-1- infected cells. Tax is a potent transcriptional activator that stimulates HTLV-1 viral and cellular gene transcription. In addition, Tax disrupts a number of cell signaling pathways involved in cell growth and survival. Glycogen synthase kinase-33 (GSK-33) is a ubiquitously expressed serine/threonine kinase present in all eukaryotic cells, which functions as a critical regulator of a wide range of cell signaling pathways. As GSK-33 is constitutively active in resting cells, it is primarily regulated through inhibition. Ser-9 phosphorylation is inhibitory to the kinase activity of GSK-33. Deregulation of GSK-33 has been linked to many human diseases such as Alzheimer’s disease and cancers. It has been reported in Aida Ulloa’s thesis that Tax inhibits GSK-33 kinase activity toward both primed and non-primed substrates through direct association. To delineate the protein-protein interaction between Tax and GSK-33, we compared the amino acid sequence of Tax with a well-characterized short peptide deriving from the GSK-33 interacting domain (GID) of Axin, and found that Tax contains a notable amino acid sequence homology to Axin GID. The region spanning Tax amino acids 185 - 205 has 24% sequence identity and 19% similarity with Axin GID. We named this region the putative Tax GID. We characterized the putative Tax GID biochemically, and discovered that a longer peptide (Tax aa. 138 - 205) of the putative Tax GID strongly inhibits GSK-3(3 kinase activity in vitro. Bioinformatics computation was used to predict the secondary structure of the Tax GID, which was further used in our docking test to identify a potential binding interface in GSK-3p. This was tested by GST pulldown and Co-IP assays using point and deletion mutants. In addition, the effects of Tax-GSK-3(3 interaction on the downstream (3-catenin and NFAT pathways were characterized by luciferase reporter assays. However, unexpectedly, we observed that Tax expression has little effects on p-catenin and NFAT transcriptional activation.


Covers not scanned.
Print version deaccessioned 2022.

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HTLV-I (Virus)
Protein-protein interactions
Glycogen synthase kinase-3


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