Targeting telomerase in hematologic malignancy

DKC1 is a transcriptional target of GATA1 and drives upregulation of telomerase activity in normal human erythroblasts

Telomerase is a ribonucleoprotein complex that maintains the length and integrity of telomeres, and thereby enables cellular proliferation. Understanding the regulation of telomerase in hematopoietic cells is relevant to the pathogenesis of leukemia, in which telomerase is constitutively activated, as well as bone marrow failure syndromes that feature telomerase insufficiency. Past studies showing high levels of telomerase in human erythroblasts and a prevalence of anemia in disorders of telomerase insufficiency provide the rationale for investigating telomerase regulation in erythroid cells. Here it is shown for the first time that the telomerase RNA-binding protein dyskerin (encoded by DKC1) is dramatically upregulated as human hematopoietic stem and progenitor cells commit to the erythroid lineage, driving an increase in telomerase activity in the presence of limiting amounts of TERT mRNA. It is also shown that upregulation of DKC1 was necessary for expansion of glycophorin A⁺ erythroblasts and sufficient to extend telomeres in erythroleukemia cells. Chromatin immunoprecipitation and reporter assays implicated GATA1-mediated transcriptional regulation of DKC1 in the modulation of telomerase in erythroid lineage cells. Together these results describe a novel mechanism of telomerase regulation in erythroid cells which contrasts with mechanisms centered on transcriptional regulation of TERT that are known to operate in other cell types. This is the first study to reveal a biological context in which telomerase is upregulated by DKC1 and to implicate GATA1 in telomerase regulation. The results from this study are relevant to hematopoietic disorders involving DKC1 mutations, GATA1 deregulation and/or telomerase insufficiency.

New prospects for targeting telomerase beyond the telomere

Telomerase activity is responsible for the maintenance of chromosome end structures (telomeres) and cancer cell immortality in most human malignancies, making telomerase an attractive therapeutic target. The rationale for targeting components of the telomerase holoenzyme has been strengthened by accumulating evidence indicating that these molecules have extra-telomeric functions in tumour cell survival and proliferation. This Review discusses current knowledge of the biogenesis, structure and multiple functions of telomerase-associated molecules intertwined with recent advances in drug discovery approaches. We also describe the fertile ground available for the pursuit of next-generation small-molecule inhibitors of telomerase.

Identification of small molecule inhibitors of telomerase activity through transcriptional regulation of hTERT and calcium induction pathway in human lung adenocarcinoma A549 cells

High telomerase activity (TA) is detected in most cancer cells; and thus, TA inhibition by drug or dietary food components is a new strategy for cancer prevention. In this report, we examined the effects of fourteen natural or synthetic compounds on TA in human lung adenocarcinoma A549 cells. The results demonstrated that some of the tested compounds inhibited TA, being 2'-hydroxy-2,3,4',6'-tetramethoxychalcone (HTMC) was the most potent among tested. In A549 cells, HTMC also inhibited the cell proliferation, decreased the expression of human telomerase reverse transcriptase (hTERT) and sequentially reduced the hTERT promoter. In soft agar assay HTMC treatment reduced the colony formation of A549 cells. Cellular fractionation and immunofluorescence assay demonstrated that there was no translocation of hTERT from nuclei to cytoplasm. Further studies revealed that the release of Ca(2+) was the underlying mechanism of suppressed TA and hTERT transcription in A549 cells exposed to HTMC. These in vitro data support the development of HTMC as a therapeutic agent for cancer complications.