Expression of Telomeres in Astrocytoma WHO Grade 2 to 4: TERRA Level Correlates with Telomere Length, Telomerase Activity, and Advanced Clinical Grade

Abstract

Cancer cells bypass replicative senescence, the major barrier to tumor progression, by using telomerase or alternative lengthening of telomeres (ALT) as telomere maintenance mechanisms (TMMs). Correlation between ALT and patient survival was demonstrated for high-grade astrocytomas. Transcription from subtelomeres produces telomeric repeat-containing RNA (TERRA), a natural inhibitor of telomerase activity (TA). This led us to evaluate correlations of TERRA and TMM with tumor grade and outcome in astrocytoma patients. SYBR Green real-time reverse transcription-polymerase chain reaction assays for quantitation of total and chromosome 2p and 18p specific TERRA levels were developed. Tumor samples from 46 patients with astrocytoma grade 2 to 4, tissue controls, and cell lines were assessed. TMMs were evaluated by measuring TA and by detecting long telomeres due to ALT. In glioblastoma multiforme (GBM) grade 4, total TERRA levels were similar to cell lines but 14-, 31-, and 313-fold lower compared with grade 3, grade 2, and nonmalignant tissue, respectively. Total TERRA levels differed from chromosomal levels. Low 2p TERRA levels correlated with dense promoter methylation of subtelomeric CpG islands, indicating that TERRA expression in gliomas may be chromosome specific and epigenetically regulated. Total TERRA levels correlated with diagnosis, with low or absent TA and the presence of ALT, and were tentatively associated with favorable patient prognosis in our cohort (P = .06). TA and short telomeres identified a subset of GBM with a median survival of only 14.8 months. TERRA and TA may be prognostic in astrocytic tumors.

Formation of telomeric repeat-containing RNA (TERRA) foci in highly proliferating mouse cerebellar neuronal progenitors and medulloblastoma

“…Our results are different from several previous reports that described either a decrease in TERRA expression between normal and colon cancer (Schoeftner and Blasco, 2008), diminished TERRA in advanced astrocytoma (Sampl et al, 2012) or a lack of expression in cancer cell lines (Ng et al, 2009;Zhang et al, 2009). The differences may reside in the use of tumor tissue compared to cancer cell lines (Ng et al, 2009;Zhang et al, 2009) (Schoeftner and Blasco, 2008;Sampl et al, 2012)].…”

Telomere Maintenance Mechanisms: Prognostic and Therapeutic Implications for the Pathologist and Oncologist

“…Thus, a loss of methylation and increased TERRA transcripts promote recombination. High concentrations of TERRA expression were found in tumors with long telomere lengths that lacked telomerase activeity [57]. These results are consistent with increased TERRA levels (determined by a Q-PCR based method described earlier) being a marker of ALTTMM [57].…”

“…As suggested by the findings of Sampl et al (2012), in an analysis of a smaller glioblastoma cohort (28 cases), the survival of individuals based on a single TMM assays did not result in a correlation with survival [57]. However, analysis of survival based on a combination of assays (TERRA levels, telomere length by Q-PCR and telomerase activity by TRAP) was associated with a trend for survival.…”

“…TERRA assay: The telomeric repeat-containing RNA (TERRA) assay is a relatively new assay that may prove valuable for accessing whether a tumor is telomerase positive [57]. TERRAs are noncoding transcripts containing telomere repeats that occur as a result of transcription at subtelomeric regions [58,59].…”

“…TERRA may inhibit telomerase activity [59,63]. A recent study demonstrated that TERRA is inversely proportional to telomerase activity [57]. TERRA transcript levels are quantified by PCR based methods, with low concentrations consistent with TelTMM.…”