ORGANIZATION AND EXPRESSION OF INTERMEDIATE FILAMENTS IN EPITHELIAL-CELLS EXPRESSING THE HTLV-I TAX PROTEIN

Intermediate filaments (IF) represent major components of the cytoskel etal network. These proteins which are differentially expressed accord ing to the cell type, constitute a dynamic structure which not only co ntributes to the cell architecture but also defines its state of diffe rentiation. Furthermore, numerous observations have shown that the IF network is altered in cells transformed by tumorigenic viruses. We hav e previously demonstrated that HTLV-I (human T-cell leukemia virus typ e I) transformed T cells were characterized by a high level of vimenti n transcripts and that the HTLV-I Tax regulatory protein was able to t ransactivate the vimentin promoter transfected into Jurkat and HeLa ce lls. To enlarge the scope of this study, we investigated the effects o f the Tax protein on the expression and organization of IF of epitheli al cells in which the IF network is composed of vimentin and cytokerat in. To this aim, we have developed a model of epithelial cells (HeLa) stably expressing the tax sequences which were introduced by using ret rovirus-mediated gene transfer. Half of the Tax expressing HeLa clones were loosely adherent to the culture surface and were displaying rema rkable morphological alterations, as ascertained by the presence of ro und-shaped or spindle-shaped cells. In these cells, expression of this viral protein correlated to a pronounced disruption in the distributi on of both the vimentin and the cytokeratin networks, as shown by immu nofluorescence and ultrastructural analysis. Indeed, vimentin filament s appeared to be concentrated in discrete spots throughout the cytopla sm, while the cytokeratin filaments appeared to form a dense ring arou nd the nucleus. More importantly, mRNA and protein analysis indicate a n enhanced expression of the cytokeratin 7 gene. These observations sh owing that the Tax protein is interfering with the cellular architectu re further document the pleiotropic action of this viral regulatory pr otein.