Basis for the differential action of aminonucleoside on normal and transformed human fibroblasts

Acid-soluble extracts of normal human fibroblasts (IMR 90 cells) exposed to [³H]aminonucleoside of puromycin ([³H]AMS) contained larger amounts of unchanged AMS than did similar extracts of their transformed counterparts (AG 2804 cells). The radioactive compounds present in IMR 90 cells were further analyzed by sequential high-voltage paper electrophoresis, enzyme digestion, and paper chromatography. In addition to unchanged [³H]AMS, only [³H]adenosine, [³H]inosine, and [³H]adenosine monophosphate could be detected, apparently derived from [³H]adenosine present in the [³H]AMS samples added to the cultures. Consistent with the absence of metabolism of AMS in IMR 90 cells was the failure to find AMS derivatives in the RNA or DNA of these cells. The content of ribonucleoside triphosphates (rNTPs) in acid-soluble extracts of IMR 90 cells was significantly reduced by AMS treatment, and nuclei or broken cell preparations obtained from AMS-treated IMR 90 cells incorporated [³H]UTP into macromolecules at approximately control rates, when supplemented with rNTPs. These findings indicated that the reduced level of rNTPs may be responsible for the AMS-induced inhibition of RNA synthesis in normal cells.