CLONING AND IDENTIFICATION OF GENES DIFFERENTIALLY EXPRESSED IN METASTATIC AND NONMETASTATIC RAT RHABDOMYOSARCOMA CELL-LINES

The objective of this study was to identify genes involved in invasion and metastasis using a rat rhabdomyosarcoma model (SMF-A and RMS-B ce ll lines), The SMF-A cell line was established from a metastatic nodul e of an induced rhabdomyosarcoma in syngeneic F344 rats, Two cell line s with defined metastatic potentials, SMF-Ai and SMF-Da, were cloned f rom the SMF-A line. The cell lime SMF-Ai is tumorigenic, highly invasi ve and highly metastatic. On the other hand, the revertant line SMF-Da is less tumorigenic, non-invasive and non-metastatic. We have isolate d from a SMF-Ai cDNA library eight cDNA clones which are differentiall y expressed by the metastatic SMF-Ai and the non-metastatic SMF-Da cel l line using Northern blot analysis. Five of these clones, smf-4, smf- 6, smf-41, smf-42 and smf-44, are overexpressed in the SMF-Da cell lin e and have homology with beta-2-microglobulin, lactate dehydrogenase, ribosomal protein L38, ribosomal protein S4 and acidic ribosomal phosp hoprotein P1, respectively. The three other clones, smf-7, smf-40 and smf-61, are overexpressed in SMF-Ai. Clones smf-40 and smf-61 show sig nificant homology with the human TB3-1 gene and the human fus gene res pectively, The clone smf-7 has no significant homology with known sequ ences, We also analyzed the expression of these clones in other rat rh abdomyosarcoma cell lines (RMS-B and their clones) and in tumors obtai ned by injection of these cell lines into rats or nude mice. Smf-61 an d smf-7 were the only clones with a differential expression pattern as sociated with the invasive or metastatic potential of all cell lines e xamined. A preliminary study of the expression of smf-7 and smf-61 in other cancer cell lines also showed mRNA expression in two human rhabd omyosarcomas and a human epidermoid carcinoma suggesting the existence of genes homologous to smf-7 and smf-61 clones in human cancers. Our findings suggest an association between the expression of smf-7 and sm f-61 and invasive or metastatic potential of rhabdomyosarcoma cells.