Differente Patterns of Telomerase Reverse Transcriptase (hTERT) mRNA Variant Expression Profiles in Patients with Myelodysplastic Syndromes (MDS) and Acute Myelogenous Leukemia (AML)

BACKGROUND: Alternative splicing of hTERT mRNA contributes to the regulation of telomerase activity in normal and neoplastic cells. The deleted variant A (Adel), lacking 36nts in the beginning of exon 6, blocks telomerase activity while the B deleted variant (Bdel), lacking exons 7 and 8, exhibits no action in terms of telomerase activation. The expression of hTERT mRNA has been investigated in myeloid malignancies with controversial results. The expression of hTERT mRNA variants has not been explored in MDS patients.

AIM: To investigate the expression of hTERT mRNA variant transcripts A+B+ (contained in the full-length product), Adel and Bdel in the bone marrow of MDS and AML untreated patients.

METHODS: Bone marrow aspirates from 27 patients with refractory anaemia or refractory cytopenia with multilineage dysplasia (RA or RCMD, defined as group A), 13 patients with refractory anaemia with excess of blasts (RAEB1 or RAEB2, defined as group B) and 17 AML patients (defined as group C) were studied. Relative expression of the above transcripts was assessed on total RNA with reverse transcription followed by real-time polymerase chain reaction (PCR). The data obtained were analyzed by using Pearson chi-square and Kruskal Wallis statistics. All individuals signed informed consent before sampling.

RESULTS: hTERT mRNA was detected in 10, 4 and 3 patients of groups A, B and C respectively. The full length product (A+B+) was detected in groups A, B and C (2/27, 4/13, 3/17 respectively) (p_A/B=0.053). Adel isoform was detected in groups A (7/27) and B (3/13) but not in group C (0/17) (p_A/C=0.022). Bdel isoform was observed in group A (3/27), B (3/13) and C (2/17). Co-expression of isoforms was observed in 2 patients of A group (Adel/Bdel, Adel/A+B+), 4 patients of group B (1 Adel/A+B+, 1 Bdel/A+B+, 2 Adel/Bdel/A+B+) and two patients of group C (Bdel/A+B+). Relative expression levels of Adel, Bdel, and A+B+ transcripts were not significantly different among patient groups.

CONCLUSIONS: Alternatively spliced hTERT variants either lack a critical reverse-transcriptase motif or produce a non-functional reverse-transcriptase. Therefore, cells may control telomerase activity by switching their hTERT mRNA variant expression profile. Our results indicate that aberrations in hTERT variant profiles, especially regarding the Adel isoform, may be implicated in the pathogenesis and progression of MDS. The increased incidence of Adel positivity among RA or RCMD patients may be connected with a decline in telomerase activity and therefore contribute to the establishment of chromosomal abnormalities. This observation underlines the need to distinguish between the different hTERT mRNA variants when investigating hTERT expression in MDS patients.