Human T-lymphotropic Virus, Type 1, Tax Protein Triggers Microtubule Reorientation in the Virological Synapse

Mohamed Nejmeddine,Amanda L Barnard,Yuetsu Tanaka,Graham P Taylor,Charles R.M Bangham

doi:10.1074/jbc.m502639200

Mohamed Nejmeddine, Amanda L Barnard + Show 3 more

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https://doi.org/10.1074/jbc.m502639200

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Abstract

We showed recently that the human T-lymphotropic virus, type 1 (HTLV-1), spreads directly from cell to cell via a virological synapse. The HTLV-1 virological synapse resembles the immunological synapse; each is a specialized contact between a lymphocyte and another cell that contains organized protein microdomains, and each involves repolarization of the T-cell microtubule cytoskeleton. However, formation of the virological synapse is not triggered by T-cell receptor-mediated antigen recognition. On the basis of our previous data, we postulated that formation of the viral synapse was triggered by a conjunction of two signals, one from HTLV-1 infection of the T-cell and one from cell-cell contact. We have recently identified ICAM-1 engagement as a cell-contact signal that causes the microtubule polarization associated with the virological synapse. Here we used confocal microscopy of T-lymphocytes naturally infected with HTLV-1 or transfected with individual HTLV-1 genes to investigate the role of the viral transcriptional transactivator protein Tax. Polarization of the microtubules was induced by cell-cell contact or by cross-linking T-cell surface molecules with monoclonal antibodies adsorbed to latex beads. We show that Tax, which is mainly found in the nucleus, is also present at two specific extranuclear sites as follows: around the microtubule organizing center in association with the cis-Golgi and in the cell-cell contact region. We show that expression of Tax provides an intracellular signal that synergizes with ICAM-1 engagement to cause the T-cell microtubule polarization observed at the virological synapse.

Highlights

We showed recently that the human T-lymphotropic virus, type 1 (HTLV-1), spreads directly from cell to cell via a virological synapse
In Naturally Infected T Cells, a Substantial Fraction of HTLV-1 Tax Protein Was Extranuclear and Colocalized with the microtubule-organizing center (MTOC)—In isolated T-cells from HTLV-1-infected subjects, Tax protein was mostly expressed in the nucleus of CD4ϩinfected T-cells (Fig. 1A)
The superposition of Tax protein staining in green (Fig. 1A) and microtubule network staining in red (Fig. 1B) showed that the extranuclear fraction of Tax protein lay adjacent to the MTOC in infected T-cells (Fig. 1C)

Summary

Introduction

We showed recently that the human T-lymphotropic virus, type 1 (HTLV-1), spreads directly from cell to cell via a virological synapse. Inhibition of Cdc prevents the following: (i) the reorientation of the MTOC in T-cells in response to an antigen-presenting cell [8]; (ii) the directional movement of macrophages toward a chemotactic signal [9]; (iii) the directional movement and the reorientation of the Golgi of fibroblasts in an in vitro wound assay [10]; and (iv) polarized basolateral secretion/endocytosis in the epithelial cell line (Madin-Darby canine kidney cells) [11]. By having established the effect of cell contact on the orientation of the HTLV-1-infected MTOC of the T-cell and the distribution of the HTLV-1 Gag protein [1], we wished to study the intracellular distribution of the HTLV-1 transcriptional activator protein (Tax) and its possible role in the formation of the virological synapse. It has been well phosphate-buffered saline; DAPI, 4Ј,6-diamidino-2-phenyindole; MES, 2-(N-morpholino)ethanesulfonic acid; PKC, protein kinase C; CREB, cAMP-response element-binding protein; TRITC, tetramethylrhodamine isothiocyanate

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