γ-ray-induced transcription and apoptosis-associated loss of 28S rRNA in interphase human lymphocytes

The authors show that in parallel to chromatin DNA cleavage, ribosomal RNA is lost in γ-ray-mediated apoptotic human lymphocytes, and demonstrate that 28S rRNA gene transcription is induced early (15 min) after irradiation, followed by selective disappearance in apoptotic cells only. The fact that newly synthesized rRNA turns over at the same rate in irradiated and untreated cell fractions, suggests the observed loss of 28S rRNA in the apoptotic cell fraction at the ribosome level is due to degradation occurring at a late stage of the apoptotic death process. Results suggest that, in addition to first-stage apoptosis-associated rDNA gene activation, cellular self-destruction at late stages is associated with processes occurring simultaneously at the ribosome level involving an endogenous RNase-like activity, and at the chromatin level involving DNA-nuclease activity. (author)