Telomere reduction in hematologic cells.

The broken ends of chromosomes are unstable, and tandem fusion of telomeres has been observed in some tumors. Using Southern blot analysis, we report here telomeric DNA changes in hematologic cells. There was some variation in the length of the telomeric DNA in normal peripheral blood mononuclear cells obtained from four different individuals, ranging from 10 to 12 kilobases (kb), but there was little difference in signal strength. In two cell lines tested, HL-60 and K562, there was a telomeric sequence reduction of 2-4 kb and there was also a diminution of signal intensity. Reduction of the telomeric DNA array was also observed in two leukemic cases tested. The peak telomere length of the leukemic cells was 5 and 4 kb before and 10 and 7 kb after treatment, respectively, and in one case there was also a reduction in copy numbers of about 50%. Since no remarkable changes were detected in the Alu and alphoid sequences in either normal or leukemic cells, it appeared that the DNA change was specific to telomeric regions. Assessment of telomeric DNA changes may aid in determining the biological significance of leukemic cells.