Unresponsiveness of both non-rearranged and rearranged c- myc to serum stimulation in a mouse plasmacytoma S194

Expression of non-rearranged and rearranged c- myc in a mouse plasmacytoma cell line S194 cultured in different serum concentration or temperature was examined. Exponentially growing S194 cells expressed a high level of rearranged c- myc and a low level of non-rearranged c- myc mRNAs. The levels of the two c- myc mRNAs were nearly the same in the cells in which growth was suppressed by lowering serum concentrations or incubation temperature in culture medium. Furthermore, even when serum-deprived S194 cells resumed growth following serum restimulation, the induction of non-rearranged c- myc mRNA, observed in a mouse T-cell lymphoma cell line BW5147, was not demonstrated. In contrast to the unchanged c- myc expression, the level of N- ras mRNA was related to changes in cell growth rate induced by changes in serum concentration in S194 cells. These results suggest that not only the rearranged c- myc but also the non-rearranged c- myc is unresponsive to serum stimulation and temperature changes, even though cell growth rate is markedly changed.