SMYD3 interacts with HTLV-1 Tax and regulates subcellular localization of Tax.
HTLV-1 Tax deregulates signal transduction pathways, transcription of genes, and cell cycle regulation of host cells, which is mainly mediated by its protein-protein interactions with host cellular factors. We previously reported an interaction of Tax with a histone methyltransferase (HMTase), SUV39H1. As the interaction was mediated by the SUV39H1 SET domain that is shared among HMTases, we examined the possibility of Tax interaction with another HMTase, SMYD3, which methylates histone H3 lysine 4 and activates transcription of genes, and studied the functional effects. Expression of endogenous SMYD3 in T cell lines and primary T cells was confirmed by immunoblotting analysis. Co-immuno-precipitaion assays and in vitro pull-down assay indicated interaction between Tax and SMYD3. The interaction was largely dependent on the C-terminal 180 amino acids of SMYD3, whereas the interacting domain of Tax was not clearly defined, although the N-terminal 108 amino acids were dispensable for the interaction. In the cotransfected cells, colocalization of Tax and SMYD3 was indicated in the cytoplasm or nuclei. Studies using mutants of Tax and SMYD3 suggested that SMYD3 dominates the subcellular localization of Tax. Reporter gene assays showed that nuclear factor-κB activation promoted by cytoplasmic Tax was enhanced by the presence of SMYD3, and attenuated by shRNA-mediated knockdown of SMYD3, suggesting an increased level of Tax localization in the cytoplasm by SMYD3. Our study revealed for the first time Tax-SMYD3 direct interaction, as well as apparent tethering of Tax by SMYD3, influencing the subcellular localization of Tax. Results suggested that SMYD3-mediated nucleocytoplasmic shuttling of Tax provides one base for the pleiotropic effects of Tax, which are mediated by the interaction of cellular proteins localized in the cytoplasm or nucleus.
Department of Medical Genome Sciences, Laboratory of Tumor Cell Biology, Graduate School of Frontier Sciences, The University of Tokyo, Minato-ku, Tokyo, Japan.
Keiyu
K
Yamamoto
Takaomi
T
Ishida
Kazumi
K
Nakano
Makoto
M
Yamagishi
Tadanori
T
Yamochi
Yuetsu
Y
Tanaka
Yoichi
Y
Furukawa
Yusuke
Y
Nakamura
Toshiki
T
Watanabe
D021581:Active Transport, Cell Nucleus; D002478:Cells, Cultured; D016356:Gene Products, tax / Q000032:analysis / Q000502:physiology*; D011495:Histone-Lysine N-Methyltransferase / Q000032:analysis / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism; D017434:Protein Structure, Tertiary
D016356:Gene Products, tax; D016328:NF-kappa B; C514970:tax protein, Human T-lymphotrophic virus 1; D011495:Histone-Lysine N-Methyltransferase; C506278:SMYD3 protein, human