To understand the role of TGFalpha in transformation, the human TGFalpha gene was placed under the control of a retroviral LTR and the mouse metallothionine promoter. Transfection of recombinant plasmids onto NIH/3T3 cells did not result in the formation of foci. However, transfected cells were shown to secrete large amounts of TGFalpha into the medium, to grow to high saturation density, and to have down-regulated receptors to EGF. DNA synthesis by TGFalpha cell lines was inhibited by anti-human TGFalpha monoclonal antibodies, suggesting potential ways to inhibit tumor growth in vivo. Comparison of TGFalpha sublines with cells transfected by a recombitant v-erbB plasmid showed v-erbB cell lines grow better in agar and produced tumors in nude mice faster than did TGFalpha cell lines. A recombinant murine retroviral vector containing the human TGFalpha gene was constructed in order to further study the effect of TGFalpha in vitro and in vivo. A retroviral construct containing the TGFalpha gene and a selectable marker, the bacterial Tn5 gene, was transfected into psi-2 cells. NIH/3T3 cells infected by high titer recombitant virus produced by psi-2 cells were found to secrete TGFalpha into the medium. The effect of TGFalpha viral infection in BALB/MK cells and in nude mice is currently being investigated.
