[ret gene from a human stomach cancer].

DNAs from 15 samples of primary stomach cancer were transfected into NIH3T3 cells. Five stomach cancer DNAs (ST1, ST3, ST6, ST7, and ST15) showed transforming activity. These transformations were caused by human cancer DNAs since human Alu repetitive sequences were detected in transformant DNAs. DNAs from transformants were screened with 22 oncogene probes available, including Ha-ras, Ki-ras, and N-ras. However, these probes did not hybridize with any human DNA in transformants. A transforming gene was cloned from an ST6-derived transformant, which turned out to be hst oncogene. By use of a probe derived from the cloned hst gene, it was shown that additional two transformants (ST7- and ST15-derived) also harboured human hst. Here I report molecular cloning of another transforming gene from an ST1-derived transformant. The transforming gene was cloned by cosmid rescue method being tagged with pSV2-gpt. The normal counterpart of the transforming gene was also cloned from a genomic phage library of human placenta DNA. Surprisingly, the transforming gene was not colinear with the placenta DNA, but was generated by the recombination of two separate genes. Comparison of the restriction maps of these genes with those of reported oncogenes showed that 3'-half of the cloned transforming gene was colinear with the 3'-half of the ret oncogene, which encodes tyrosine kinase domain. It was suggested that this gene was activated by DNA rearrangement upon transfection, placing a transcriptionally active promoter on upstream of the kinase domain. Among 4 primary transformants derived from ST1 two did not have human ret oncogene, indicating that other transforming genes were involved in these transformation events.