Telomere Length Is Related to Alternative Splice Patterns of Telomerase in Thyroid Tumors

Abstract

Telomere dysfunction and aberrant telomerase expression play important roles in tumorigenesis. In thyroid tumors, three possibly inhibitory splice variants of the active full-length isoform of human telomerase reverse transcriptase (hTERT) may be expressed. These variants might regulate telomerase activity and telomere length because it is the fraction of the full-length isoform, rather than the total transcript level, that correlates with enzymatic activity. Telomerase reactivation may be critical in the early stages of tumorigenesis, when progressive telomere shortening may be limiting cell viability. The aim of this study was to investigate the relationship between telomere length and hTERT splice variant expression patterns in benign and well-differentiated malignant thyroid tumors. Telomere lengths of 61 thyroid tumors were examined by fluorescence in situ hybridization, comparing tumors with adjacent normal thyroid tissue on the same slide. Expression patterns of hTERT splice variants were evaluated by quantitative and nested RT-PCR. Telomere length was inversely correlated with percentage of full-length hTERT expression rather than with total hTERT expression levels. Short telomeres and high fractions of full-length hTERT transcripts were associated with follicular and papillary thyroid carcinomas, whereas long telomeres and low levels of full-length hTERT were associated with benign thyroid nodules. Intermediate levels of full-length hTERT and telomere length were found in follicular variant of papillary thyroid carcinomas and follicular adenomas.

Characterization of human telomerase reverse transcriptase promoter methylation and transcription factor binding in differentiated thyroid cancer cell lines

“…RNA was reverse transcribed to cDNA using SuperScript III Reverse Transcriptase (ThermoFisher) according to manufacturer instructions. Quantitative PCR was performed as previously described with SYBR Green PCR Master Mix (ThermoFisher), with primers designed to detect the full‐length TERT transcript levels . The expression level of TERT was normalized to GAPDH .…”

“…Quantitative PCR was performed as previously described with SYBR Green PCR Master Mix (ThermoFisher), with primers designed to detect the full-length TERT transcript levels. 43 The expression level of TERT was normalized to GAPDH.…”

Microenvironmental Regulation of Telomerase Isoforms in Human Embryonic Stem Cells

“…The dynamic changes in TERT isoform transcript abundance we observed in hESCs cultured under varying O 2 conditions and in microenvironments that maintain or impede proliferation in the undifferentiated state suggest that either the levels of specific TERT isoforms or the relative proportions of the entire TERT isoform expression profile are important for hESC self-renewal and differentiation. Although the mechanism and function of TERT alternative splicing is presently vague [99], the pattern of TERT splice variants correlates with loss of telomerase activity during development [35] and tumor grade [100], suggesting that differential splicing may be a means of regulating TERT gene expression without altering overall transcription levels under certain microenvironments. Interestingly, TERT appears to be regulated by alternative splicing under hypoxic conditions, involving a switch in the splice pattern in favor of the active full-length isoform in ovarian carcinoma cells [83].…”

Cytokines and STATs in Liver Fibrosis

“…However, the roles of STAT3 in liver fibrogenesis remain largely unknown. Hepatocyte-specific STAT3 knockout mice displays a higher degree of liver fibrosis compared with wild-type mice in various models of liver fibrosis induced by CCl 4 administration (Wang et al, 2011b), feeding with a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet (Plum et al, 2010), feeding with a choline-deficient, ethionine-supplemented (CDE) diet (Kroy et al, 2010), or upon deletion of the multidrug resistance gene 2 (Mair et al, 2010). The obvious mechanism by which hepatocyte STAT3 protects against liver fibrosis is that hepatocyte STAT3 activation prevents hepatocellular damage and subsequently reduces injury-driven liver fibrogenesis.…”