Telomerase activity in human leukemic cells with or without monosomy 7 or 7q-

Abstract

Background: In bone marrow material from patients with various leukemias we noted that samples with either a deletion on the long arm of one chromosome 7 (7q-) or a monosomy 7 had a higher telomerase activity. Considering that introduction of a chromosome 7 into a cancer cell line had been reported to eliminate telomerase activity, that 7q- is a common negative prognostic finding in cancers, and that the deleted segment (band 7q31) contains an unidentified tumor suppressor gene, we wondered if this gene might be a telomerase inhibitor.

Results: We found no significant difference in telomerase activity between the three groups of patient samples. In contrast to reports on tumor cell lines we observed no amplification of the telomerase genes.

Methods: We analyzed telomerase activity and copy number of the telomerase genes hTERT and hTR in frozen archival bone marrow samples from leukemia patients with a referral diagnosis of AML, and either a monosomy for chromosome 7, a deletion on the long arm of chromosome 7 (7q-), or none of these aberrations. Telomerase activity was measured with a commercially available kit, and the copy number of the telomerase genes was tested by FISH.

Conclusions: We found no evidence of a telomerase inhibitor in band 7q31. The lack of telomerase gene amplification found in cell lines from solid tumors could reflect that this amplification is a property of solid tumors, not of hematological cancers.

Figure 1

CGH analysis of chromosome 7 in the 7q- samples and FISH analysis of the relevant regions on chromosomes 3, 5 and 7. A. CGH analysis of pooled DNA from the 7q- samples hybridized against control DNA from a normal male donor. The CGH profile for chromosome 7 is shown. A deletion is seen in the 7q31 region as indicated on the idiogram. B. Triple color hybridization for 7CEN/D7S522, hTERT, and hTR. 7CEN (orange arrows) and hTR (yellow arrows) appear in green. In the microscope the hTR signal was bright and clearly visible, but in the present representation it appears weak due to the auto exposure in the green channel being governed by the stronger 7CEN signal (compare with panel D). Both D7S522 (orange arrows) and hTERT (red arrows) appear red in this representation. In the microscope, each of the two probes appeared in its recognizable reddish color, but the difference could not be reproduced here. C. Dual color hybridization of hTERT (red) and chromosome 7 probes (green centromere juxtapositioned with red 7S522). While both hTERT loci are labeled, one chromosome 7 has only a centromere signal, and not a 7q31 signal. D. Dual color hybridization of the hTR and hTERT probes showing two signals for each probe. This was the general finding in all 65 samples. In the absence of the green centromere 7 signal the hTR probe is clearly visible after auto exposure.

Figure 2

ELISA readings for telomerase activity in the three categories of patient samples.

Figure 3

Correlation between ELISA readings for telomerase activity and the frequency of 7q31 FISH signals in individual samples from the 7q- patients.