Changes in chromatin structure during the aging of cell cultures as revealed by differential scanning calorimetry.
Nuclei from cultured human cells were examined by differential scanning calorimetry. Their melting profiles revealed four structural transitions at 60, 76, 88, and 105 degrees C (transitions I-IV, respectively). In immortalized (i.e., tumor) cell cultures and in normal cell cultures of low passage number, melting profiles were dominated by the 105 degrees C transition (transition IV), but in vitro aging of normal and Werner syndrome cells was associated with a marked decrease in transition IV followed by an increase in transition III at the expense of transition IV. At intermediate times in the aging process, much DNA melted at a temperature range (95-102 degrees C) intermediate between transitions III and IV, and this is consistent with the notion that aging of cell cultures is accompanied by an increase in single-strand character of the DNA. Calorimetric changes were observed in the melting profile of nuclei from UV-irradiated tumor cells that resembled the age-induced intermediate melting of chromatin. It is suggested that aging is accompanied by an increase in single-stranded character of the DNA in chromatin, which lowers its melting temperature, followed by strand breaks in the DNA that destroy its supercoiling potential.
Department of Biochemistry, University of California, Berkeley 94720.
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D002152:Calorimetry, Differential Scanning / Q000379:methods; D002455:Cell Division; D002460:Cell Line; D002467:Cell Nucleus / Q000528:radiation effects / Q000648:ultrastructure; D002843:Chromatin / Q000528:radiation effects / Q000648:ultrastructure*; D004247:DNA / Q000648:ultrastructure; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D009691:Nucleic Acid Denaturation; D014407:Tumor Cells, Cultured / Q000166:cytology; D014466:Ultraviolet Rays; D014898:Werner Syndrome
D002843:Chromatin; D004247:DNA