Telomerase reverse transcriptase promotes cancer cell proliferation by augmenting tRNA expression
Ekta Khattar, … , Yuin Han Loh, Vinay Tergaonkar
Ekta Khattar, … , Yuin Han Loh, Vinay Tergaonkar
Published September 19, 2016
Citation Information: J Clin Invest. 2016;126(10):4045-4060. https://doi.org/10.1172/JCI86042.
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Research Article Oncology

Telomerase reverse transcriptase promotes cancer cell proliferation by augmenting tRNA expression

Abstract

Transcriptional reactivation of telomerase reverse transcriptase (TERT) reconstitutes telomerase activity in the majority of human cancers. Here, we found that ectopic TERT expression increases cell proliferation, while acute reductions in TERT levels lead to a dramatic loss of proliferation without any change in telomere length, suggesting that the effects of TERT could be telomere independent. We observed that TERT determines the growth rate of cancer cells by directly regulating global protein synthesis independently of its catalytic activity. Genome-wide TERT binding across 5 cancer cell lines and 2 embryonic stem cell lines revealed that endogenous TERT, driven by mutant promoters or oncogenes, directly associates with the RNA polymerase III (pol III) subunit RPC32 and enhances its recruitment to chromatin, resulting in increased RNA pol III occupancy and tRNA expression in cancers. TERT-deficient mice displayed marked delays in polyomavirus middle T oncogene–induced (PyMT-induced) mammary tumorigenesis, increased survival, and reductions in tRNA levels. Ectopic expression of either RPC32 or TERT restored tRNA levels and proliferation defects in TERT-depleted cells. Finally, we determined that levels of TERT and tRNA correlated in breast and liver cancer samples. Together, these data suggest the existence of a unifying mechanism by which TERT enhances translation in cells to regulate cancer cell proliferation.

Authors

Ekta Khattar, Pavanish Kumar, Chia Yi Liu, Semih Can Akıncılar, Anandhkumar Raju, Manikandan Lakshmanan, Julien Jean Pierre Maury, Yu Qiang, Shang Li, Ern Yu Tan, Kam M. Hui, Ming Shi, Yuin Han Loh, Vinay Tergaonkar

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Figure 7

RPC32 and TERT can rescue cell proliferation upon TERT depletion.

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RPC32 and TERT can rescue cell proliferation upon TERT depletion. (A) A ...
(A) A cell proliferation assay was performed in BLM C250T, BLM WT, and BLM WT cells infected with RPC32-expressing vector. Graph shows fluorescence intensity measured using an Alamar Blue viability assay. n = 3. (B) A cell proliferation assay was performed in BLM C250T, BLM WT, and BLM WT cells infected with TERT or TERT DN or with TERT 601-1132 or TERT 346-925 constructs. n = 3. (C) BLM WT cells were infected with vector or TERT or with TERT DN or RPC32 and expanded along with BLM C250T cells infected with vector. Following infection, the cells were xenografted s.c. into NOD/SCID mice and allowed to form tumors. After 15 days, tumors were harvested and analyzed. Figure shows images of 3 independent tumors of each cell type; the number of tumors obtained is indicated. (D) Weights of tumors produced in C. (E) RNA was extracted from tumors obtained from C. Graph shows the relative expression of pre–tRNA-Leu normalized against actin levels in tumors. All error bars indicate the mean ± SEM. **P < 0.001 and #P > 0.05, by 1-way ANOVA with Tukey’s multiple comparisons test.