[Analysis of c-onc genes in choriocarcinoma cells]

Regulatory or structural alterations of c-onc genes including amplification, rearrangement and point mutation was implicated in the causation of various malignant tumors. However, such changes of molecular levels have not been reported so far in choriocarcinoma cells. In the present study, thus, 5 choriocarcinoma cell lines were analyzed by hybridization using 16 oncogene probes. By Southern blot hybridization of DNA extracted from these cells, 8 fold amplification of c-myc gene and rearrangement of c-fms gene were shown in ENAMI cells, although the role of these alterations remained unknown. Northern blot hybridization performed simultaneously demonstrated multiple expression of c-onc genes. 4 choriocarcinoma cell lines (HCCM, CHl, CCl, ENAMI) expressed at least 11 c-onc genes (H-ras, K-ras, N-ras, c-myc, N-myc, fos, fms, src, yes, erb B and raf); though the degree of expression of H-ras, C-myc, erb B and fms in these cells was either similar or enhanced as compared with normal fibroblast, the expression of two c-onc genes (N-myc and fos) was extremely enhanced. However, expression of K-ras and myb was either low or not detected. The multiple expression of c-onc genes seems to reflect partly on growth advantages of trophoblast. Transfection assay using NIH3T3 cells failed to form any transformed foci. Since choriocarcinoma cells which derived from the transformation of trophoblast of complete mole possess the genetic characteristics identical to the one of cells of complete mole, chromosomal instability was assumed to play a major role for multiple oncogene expression in choriocarcinoma cells.