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Purpose/Method.Transfection experiments have been used to identify activated oncogenes in a wide variety of tumour types. Here we describe the use of transfection experiments utilizing DNA from a human pleomorphic liposarcoma to identify a novel gene, designatedlipwhich maps to chromosome 19.Results. lipwas expressed in all sarcoma cell lines examined and a wide variety of normal tissues. Sequencing of cDNAs prepared from transcripts of the normallipgene indicates thatlipis predicted to encode a 966 amino acid protein with a region of homology to proteins such asvav, dbl, lbcandect-2which act as GDP–GTP exchange factors for the RAS superfamily of small GTP-binding proteins, and the N-terminal 830 amino acids are identical to the recently identified gene p115-RhoGEF, an exchange factor for RHOA. In transfectants,liphas undergone a rearrangement which results in C-terminal truncation of the predicted LIP protein. However, we failed to detect this alteration in the primary liposarcoma used in the original transfection experiments, or in other sarcoma specimens examined.Discussion.When considered together, these observations suggest that transforminglipsequences represent an alternatively spliced form of p115-RhoGEF that is activated for transformation by C-terminal truncation during transfection, and is not widely involved in sarcoma development.

Purpose. Amplification of genetic sequences on chromosome 12q13 is frequently found in soft tissue tumours. However, for theMDM2gene, over-expression of the MDM2 protein has not always been shown to accompany gene amplification, raising the possibility that amplification of genetic sequences targets alternative genes on chromosome 12q13 for over-expression. To investigate this discrepancy, we have examined 129 soft tissue tumours for amplification of theMDM2gene using Southern analysis, and 39 of these tumours were also examined by immunohistochemical staining for MDM2 over-expression.Results. Gene amplification was identified in 14/114 (12.3%) of the malignant tumours, but was not identified in any of the benign tumours; 21/39 (54%) of the malignant tumours also demonstrated MDM2 over-expression. Within this group theMDM2gene was over-expressed in every tumour in which the gene amplification was found, and over-expression in the absence of gene amplification was also found in an additional 10 tumours.Discussion. These data demonstrate a clear correlation between the presence ofMDM2amplification and MDM2 over-expression, and provide persuasive evidence therefore that the amplification of genetic sequences on chromosome 12q13 in soft tissue sarcomas targets theMDM2gene for over-expression. These data also indicate that alternative mechanisms may contribute to MDM2 over-expression within some tumours.