Regulation of the expression of the human vimentin gene: application to cellular immortalization

Vimentin is an intermediate filament protein mainly specific of the mesoderm in vivo. In vitro vimentin synthesis is characteristic of proliferating cells, regardless of their embryonal origin, and is switched off upon differentiation of certain precursor cells. Vimentin gene expression is upregulated in some metastatic tumour cells, appearing as a marker of oncogenic progression. The vimentin network has been suggested to participate in several steps of viral infections. The promoter of the vimentin gene is comprised of multiple elements responsible for its complex transcriptional regulation. Among them, an NF-kappa B- and two AP1-binding sites mediate growth factor responsiveness. Two negative elements are present, one of which is deregulated by the HTLV-1 activator protein Tax. Transcription factor PEA3, encoded by a member of the ets oncogene family, activates the vimentin promoter in mammary tumour cells. In vitro, 878 base pairs of the vimentin 5'-regulatory region are sufficient to give high levels of transcription. These sequences were coupled to the SV40 large T antigen-encoding gene to achieve immortalization of new cell lines, either by transfection of primary cultures, or by derivation of cell explants from transgenic mice expressing the vimentin-SV40 construct. This allowed us, for instance, to immortalize endothelial, myogenic or renal epithelial cells, otherwise difficult to maintain in culture without loss of their differentiated phenotypes.