Several oncogenes isolated by the NIH/3T3 transformation assay, i.e., dbl, dbs, lbc, lfc, lsc, net, ost and tim, contain a Dbl homology (DH) and a pleckstrin-homology (PH) domain and act as GEFs (guanine nucleotide exchange factors) for Rho-like GTPases. In a search for genes with oncogenic potential in DNA from the monocytic leukaemia cell line U937, we identified an amino-terminal truncated form of gef-h1, a gene encoding a GEF for RhoA. These data support the idea that a systematic search for mutations and/or deletions of GEFs in human cancer is promising.

By means of the tumorigenicity assay applying DNA from a patient with a gastric carcinoma (MA) we have already reported the identification of the putative oncogene myeov. In addition we have shown its involvement in t(11;14)positive multiple myelomas and amplifications of breast tumours and esophageal carcinomas. The failure of myeov cDNA to induce tumour formation in NIH/3T3 cells prompted us to analyze the human sequences present in our MA-T1a1 tertiary transfectants. Sequence analysis revealed the presence of the human oncogene hst (fgf4) at a distance of ~9kb from the myeov gene in our MA-T1a1 tertiary transfectants. Both myeov and hst (fgf4) are normally situated ~475-kb apart at band 11q13, a region that is frequently amplified and overexpressed in various tumours. Southern and Northern blot analyses confirmed our sequence data and showed rearrangement of hst sequences during the transfection process and its expression in our MA-T1a1 tertiary transfectants.