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Quantitative relationship between functionally active telomerase and major telomerase components (hTERT and hTR) in acute leukaemia cells.

Ohyashiki JH, Hisatomi H, Nagao K, Honda S, Takaku T, Zhang Y, Sashida G, Ohyashiki K - Br. J. Cancer (2005)

Bottom Line: We therefore developed a rapid and sensitive method to quantify hTERT and its splicing variants as well as the hTR by a Taqman real-time reverse transcriptase-polymerase chain reaction to determine whether their altered expression may contribute to telomere attrition in vivo or not.In spite of high copy numbers of full-length hTERT mRNA, telomerase activity was low in some cases correlating with low copy numbers of hTR, raising the possibility that alteration of the hTR : hTERT ratio may affect functionally active telomerase activity in vivo.The spliced nonactive hTERT mRNA tends to be lower in patients with high telomerase activity, suggesting that this epiphenomenon may play some role in telomerase regulation.

View Article: PubMed Central - PubMed

Affiliation: Intractable Immune System Diseases Research Center, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku, Tokyo 160-0023, Japan. junko@hh.iij4u.or.jp

ABSTRACT
Functionally active telomerase is affected at various steps including transcriptional and post-transcriptional levels of major telomerase components (hTR and human telomerase reverse transcriptase (hTERT)). We therefore developed a rapid and sensitive method to quantify hTERT and its splicing variants as well as the hTR by a Taqman real-time reverse transcriptase-polymerase chain reaction to determine whether their altered expression may contribute to telomere attrition in vivo or not. Fresh leukaemia cells obtained from 38 consecutive patients were used in this study. The enzymatic level of telomerase activity measured by TRAP assay was generally associated with the copy numbers of full-length hTERT+alpha+beta mRNA (P=0.0024), but did not correlate with hTR expression (P=0.6753). In spite of high copy numbers of full-length hTERT mRNA, telomerase activity was low in some cases correlating with low copy numbers of hTR, raising the possibility that alteration of the hTR : hTERT ratio may affect functionally active telomerase activity in vivo. The spliced nonactive hTERT mRNA tends to be lower in patients with high telomerase activity, suggesting that this epiphenomenon may play some role in telomerase regulation. An understanding of the complexities of telomerase gene regulation in biologically heterogeneous leukaemia cells may offer new therapeutic approaches to the treatment of acute leukaemia.

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The quantitative relationship between functionally active telomerase activity and its components. Shapes of three elements (full-length hTERT, hTR and relative telomerase activity) are different in patients with low telomerase activity despite high full-length hTERT expression (A–C) and that in a patient with high telomerase activity (D).
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fig5: The quantitative relationship between functionally active telomerase activity and its components. Shapes of three elements (full-length hTERT, hTR and relative telomerase activity) are different in patients with low telomerase activity despite high full-length hTERT expression (A–C) and that in a patient with high telomerase activity (D).

Mentions: To address the question as to why some patients show low telomerase activity despite high hTERT+α+β expression, we next compared the ratio of hTR and hTERT. The Group-L patients showed significantly lower copy numbers of hTR (P=0.0284), and the hTR/hTERT ratio was significantly lower than those in Group-H patients (P=0.0094) (Figure 4). This indicates the possibility that the combination of full-length hTERT and hTR is necessary to create a functionally active telomerase activity in leukaemia cells in vivo. The quantitative relationships between functionally active telomerase activity and its components are shown in Figure 5. There was an obvious difference between patients with low telomerase activity, despite high full-length hTERT expression (UPN41, 40 and 44, Figure 5A–C, respectively) and patients with high telomerase activity (UPN15, Figure 5D). We next analysed the mutation of the hTR gene in three patients showing a marked discrepancy between hTERT+α+β expression and telomerase activity, in order to determine whether this phenomenon is related to mutation of hTR. No case showed mutation of hTR gene within the limit of our primers. This indicates that the discrepancy between expression of full-length hTERT and functionally active telomerase activity is possibly due to the quantity of hTR but not to the gene structure of hTR.


Quantitative relationship between functionally active telomerase and major telomerase components (hTERT and hTR) in acute leukaemia cells.

Ohyashiki JH, Hisatomi H, Nagao K, Honda S, Takaku T, Zhang Y, Sashida G, Ohyashiki K - Br. J. Cancer (2005)

The quantitative relationship between functionally active telomerase activity and its components. Shapes of three elements (full-length hTERT, hTR and relative telomerase activity) are different in patients with low telomerase activity despite high full-length hTERT expression (A–C) and that in a patient with high telomerase activity (D).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2361762&req=5

fig5: The quantitative relationship between functionally active telomerase activity and its components. Shapes of three elements (full-length hTERT, hTR and relative telomerase activity) are different in patients with low telomerase activity despite high full-length hTERT expression (A–C) and that in a patient with high telomerase activity (D).
Mentions: To address the question as to why some patients show low telomerase activity despite high hTERT+α+β expression, we next compared the ratio of hTR and hTERT. The Group-L patients showed significantly lower copy numbers of hTR (P=0.0284), and the hTR/hTERT ratio was significantly lower than those in Group-H patients (P=0.0094) (Figure 4). This indicates the possibility that the combination of full-length hTERT and hTR is necessary to create a functionally active telomerase activity in leukaemia cells in vivo. The quantitative relationships between functionally active telomerase activity and its components are shown in Figure 5. There was an obvious difference between patients with low telomerase activity, despite high full-length hTERT expression (UPN41, 40 and 44, Figure 5A–C, respectively) and patients with high telomerase activity (UPN15, Figure 5D). We next analysed the mutation of the hTR gene in three patients showing a marked discrepancy between hTERT+α+β expression and telomerase activity, in order to determine whether this phenomenon is related to mutation of hTR. No case showed mutation of hTR gene within the limit of our primers. This indicates that the discrepancy between expression of full-length hTERT and functionally active telomerase activity is possibly due to the quantity of hTR but not to the gene structure of hTR.

Bottom Line: We therefore developed a rapid and sensitive method to quantify hTERT and its splicing variants as well as the hTR by a Taqman real-time reverse transcriptase-polymerase chain reaction to determine whether their altered expression may contribute to telomere attrition in vivo or not.In spite of high copy numbers of full-length hTERT mRNA, telomerase activity was low in some cases correlating with low copy numbers of hTR, raising the possibility that alteration of the hTR : hTERT ratio may affect functionally active telomerase activity in vivo.The spliced nonactive hTERT mRNA tends to be lower in patients with high telomerase activity, suggesting that this epiphenomenon may play some role in telomerase regulation.

View Article: PubMed Central - PubMed

Affiliation: Intractable Immune System Diseases Research Center, Tokyo Medical University, 6-7-1, Nishishinjuku, Shinjuku, Tokyo 160-0023, Japan. junko@hh.iij4u.or.jp

ABSTRACT
Functionally active telomerase is affected at various steps including transcriptional and post-transcriptional levels of major telomerase components (hTR and human telomerase reverse transcriptase (hTERT)). We therefore developed a rapid and sensitive method to quantify hTERT and its splicing variants as well as the hTR by a Taqman real-time reverse transcriptase-polymerase chain reaction to determine whether their altered expression may contribute to telomere attrition in vivo or not. Fresh leukaemia cells obtained from 38 consecutive patients were used in this study. The enzymatic level of telomerase activity measured by TRAP assay was generally associated with the copy numbers of full-length hTERT+alpha+beta mRNA (P=0.0024), but did not correlate with hTR expression (P=0.6753). In spite of high copy numbers of full-length hTERT mRNA, telomerase activity was low in some cases correlating with low copy numbers of hTR, raising the possibility that alteration of the hTR : hTERT ratio may affect functionally active telomerase activity in vivo. The spliced nonactive hTERT mRNA tends to be lower in patients with high telomerase activity, suggesting that this epiphenomenon may play some role in telomerase regulation. An understanding of the complexities of telomerase gene regulation in biologically heterogeneous leukaemia cells may offer new therapeutic approaches to the treatment of acute leukaemia.

Show MeSH
Related in: MedlinePlus