Expression cDNA cloning of a novel oncogene with sequence similarity to regulators of small GTP-binding proteins.

We generated a cDNA expression library from a human mammary epithelial cell line for detection of novel oncogenes by focus formation assay in NIH3T3 cells. A morphologically unique focus was identified and the transforming plasmid was isolated. The transforming gene, designated TIM, encoded a predicted protein species of 60 kDa containing a Dbl-Homology (DH) motif. This motif is also present in other growth regulatory molecules including Bcr, Cdc24, Vav, Ras-grf, and Ect2 which have been implicated as regulators of small GTP-binding proteins. NIH3T3 cells transfected with TIM expression plasmid showed altered growth properties in vitro and were tumorigenic when injected into nude mice. The 6.5 kilobasepair (kb) transcript of the TIM gene was mainly expressed in kidney, liver, pancreas, lung, and placenta. By analysing a panel of human-hamster somatic cell hybrids, we localized the TIM gene to human chromosome 7.