Changes in gene expression following neoplastic transformation of rat myogenic cells

Two malignant sublines, M4 and RMS4 , were previously derived from the recloned L6 line of rat myogenic cells. Comparative studies in tissue culture and inoculation into suckling rats indicated that M4 cells and RMS4 cells may be considered as low-malignant and high-malignant cells, respectively, while L6 cells are not malignant. In the present work, we used extracts from L6 cells, M4 cells, and RMS4 cells collected during the period of exponential growth, to compare their polyadenylic acid-containing messenger RNA (mRNA) populations and the corresponding cell-free translation products. Analysis of the hybridization kinetics between radioactive complementary DNA and homologous or heterologous cellular RNAs indicated that L6 cells contained about 28,000 distinct polyadenylic acid-containing mRNA sequences of 1.8 kilobases each, of which 2,000 to 2,500 and 4,000 to 5,000 were missing (or at least were very infrequent) in M4 cells and RMS4 cells, respectively. Using a minor fraction of the RMS4 cell complementary DNAs, partially purified through repeated complementary DNA-RNA hybridization cycles, it was further shown that RMS4 cells contained at least 700 to 800 distinct mRNA species, mainly belonging to the class of low abundance, which appeared to be absent in L6 cells. Most of these mRNA species were also found with a lower frequency in M4 cells. Bidimensional analysis of the cell-free translation products directed by polyadenylic acid-containing mRNA revealed some remarkable differences, in particular the synthesis in a RMS4 cell extract of at least three major polypeptides, possibly related either to the neoplastic process itself or to the stage of malignant transformation.