hTERT gene amplification and increased mRNA expression in central nervous system embryonal tumors

Abstract

High-level gains at 5p15, a chromosomal region including the human telomerase catalytic protein subunit (hTERT) gene, have been documented in several medulloblastomas. We therefore analyzed hTERT gene dosage in a group of medulloblastomas and other embryonal brain tumors using differential PCR. Amplification of the hTERT locus was detected in 15 of 36 (42%) tumors examined. To correlate gene amplification with message level, we used real-time quantitative PCR to measure hTERT mRNA in 50 embryonal brain tumors. hTERT mRNA was detected in all but one of these cases, and mRNA level correlated significantly with gene dosage (r = 0.82). Log-rank analysis of survival data revealed a trend toward poor clinical outcomes in patients with medulloblastomas containing high hTERT mRNA levels, but clinical follow-up was relatively short and the association was not statistically significant (P = 0.078). Comparative genomic hybridization was used to further analyze the tumor with the greatest hTERT gene dosage and mRNA level, a recurrent medulloepithelioma. hTERT was amplified in the recurrent tumor but not in the primary lesion, suggesting this locus can be involved in tumor progression. Our data indicate that hTERT gene amplification is relatively common in embryonal brain tumors, and that increased expression of hTERT mRNA may be associated with biologically aggressive tumor behavior.

Figure 1.

hTERT gene amplification detected by differential PCR. In cases 45, 15, and 11, hTERT and 5qSTS sequences are amplified in a roughly 1:1 ratio. In case 50, the hTERT product is 17-fold more abundant, consistent with gene amplification at the locus.

Figure 2.

High hTERT expression is associated with poor clinical outcome. Log-rank analysis of Kaplan-Meier survival curves for patients with above or below median hTERT mRNA level reveals a trend toward better clinical outcomes for patients in the low hTERT group (P = 0.078).

Figure 3.

Chromosomal alterations in a medulloepithelioma detected by CGH. A: Thin vertical lines on the right side of the chromosome ideograms indicate gains; thin lines on the left represent losses. High-level gains are depicted as thick lines. Gains and losses in the primary and recurrent tumors from patient 50 are shown, with alterations in the primary lesion represented using dotted lines, and in the recurrent one using solid lines. B: While the primary tumor shows no gains or losses, the recurrent medulloepithelioma has a high level gain at 5p14-pter and loss of 5q. Each line represents a difference ratio of 0.25.