Tel (ETV6) is an ETS transcription factor that is found fused to a variety of tyrosine kinases and transcription factors in lymphoid and myeloid leukemias and in fibrosarcoma and mesoblastic nephroma. It contains two functional domains, a pointed (PNT) protein interaction domain and a DNA binding domain (DBD).

Retroviral transduction of a wild-type Tel cDNA into a clonal subline of NIH3T3 fibroblasts resulted in a reproducible, striking morphological change: at confluency, the cells reorganized into a specific ‘bridge-like’ pattern over the entire surface of the culture dish, and started migrating, thereby leaving circular holes in the monolayer. Thereafter cellular cord formation became apparent. This morphological change is most reminiscent to that of endothelial cells that differentiate into tubes in vitro. This effect may relate to the role of Tel in angiogenesis: a Tel knockout study showed that early in development Tel is required for the maintenance of the cell layer surrounding the endothelial cells in the yolk sac. Electron microscopic examination of the fibroblastic cellular cords revealed that they did not contain a lumen. Retroviral transduction of endothelial cells did induce aggregation of the cells but not cellular cord or tube formation. We inhibited the Tel-induced morphological change in the fibroblasts by coating the culture dishes with high but not low concentrations of fibronectin and collagen IV. Transduction of the fibroblasts with deletion mutants or point mutants of Tel, or with MN1-Tel and VP16-Tel, showed that both the pointed domain and the DNA binding domain of Tel are required to induce the morphological change. MN1-Tel and VP16-Tel as well as the ETS transcription factors Fli1 and Ets1, both expressed in endothelial cells, did not result in this morphological change. These results strongly suggest that native Tel, and probably target genes of Tel are causally involved in the induction of this phenotypic change.

We therefore searched for differentially expressed genes in Tel- versus vector-transduced fibroblasts using DNA filter arrays and antibody-based techniques. Thus far, 4 differentially expressed genes have been found that might relate to the observed phenotype. Expression differences were found to be consistent (present in at least 3 independent experiments), but low (1.5- to 3-fold different). More putative Tel target genes that function in ECM-build-up, cell adhesion and proteolysis are under investigation.