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Journal of Virology, May 2008, p. 4343-4353, Vol. 82, No. 9
0022-538X/08/$08.00+0     doi:10.1128/JVI.02054-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

XBP-1, a Novel Human T-Lymphotropic Virus Type 1 (HTLV-1) Tax Binding Protein, Activates HTLV-1 Basal and Tax-Activated Transcription{triangledown}

Sebastian C. Y. Ku,1 Jialing Lee,1 Joanne Lau,1 Meera Gurumurthy,1 Raymond Ng,1 Siew Hui Lwa,1 Joseph Lee,1 Zachary Klase,2 Fatah Kashanchi,2 and Sheng-Hao Chao1*

Expression Engineering Group, Bioprocessing Technology Institute, 20 Biopolis Way, #06-01 Centros, Singapore 138668, Singapore,1 Department of Biochemistry and Molecular Biology, George Washington University School of Medicine, Washington, DC 200372

Received 17 September 2007/ Accepted 11 February 2008

X-box binding protein 1 (XBP-1), a basic leucine zipper transcription factor, plays a key role in the cellular unfolded protein response (UPR). There are two XBP-1 isoforms in cells, spliced XBP-1S and unspliced XBP-1U. XBP-1U has been shown to bind to the 21-bp Tax-responsive element of the human T-lymphotropic virus type 1 (HTLV-1) long terminal repeat (LTR) in vitro and transactivate HTLV-1 transcription. Here we identify XBP-1S as a transcription activator of HTLV-1. Compared to XBP-1U, XBP-1S demonstrates stronger activating effects on both basal and Tax-activated HTLV-1 transcription in cells. Our results show that both XBP-1S and XBP-1U interact with Tax and bind to the HTLV-1 LTR in vivo. In addition, elevated mRNA levels of the gene for XBP-1 and several UPR genes were detected in the HTLV-1-infected C10/MJ and MT2 T-cell lines, suggesting that HTLV-1 infection may trigger the UPR in host cells. We also identify Tax as a positive regulator of the expression of the gene for XBP-1. Activation of the UPR by tunicamycin showed no effect on the HTLV-1 LTR, suggesting that HTLV-1 transcription is specifically regulated by XBP-1. Collectively, our study demonstrates a novel host-virus interaction between a cellular factor XBP-1 and transcriptional regulation of HTLV-1.

* Corresponding author. Mailing address: Expression Engineering Group, Bioprocessing Technology Institute, 20 Biopolis Way, #06-01 Centros, Singapore 138668, Singapore. Phone: (65) 6478-8899. Fax: (65) 6478-9561. E-mail: jimmy_chao{at}bti.a-star.edu.sg

{triangledown} Published ahead of print on 20 February 2008.

Journal of Virology, May 2008, p. 4343-4353, Vol. 82, No. 9
0022-538X/08/$08.00+0     doi:10.1128/JVI.02054-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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