Telomerase Variant A279T Induces Telomere Dysfunction and Inhibits Non-Canonical Telomerase Activity in Esophageal Carcinomas

Abstract

BackgroundAlthough implicated in the pathogenesis of several chronic inflammatory disorders and hematologic malignancies, telomerase mutations have not been thoroughly characterized in human cancers. The present study was performed to examine the frequency and potential clinical relevance of telomerase mutations in esophageal carcinomas.MethodsSequencing techniques were used to evaluate mutational status of telomerase reverse transcriptase (TERT) and telomerase RNA component (TERC) in neoplastic and adjacent normal mucosa from 143 esophageal cancer (EsC) patients. MTS, flow cytometry, time lapse microscopy, and murine xenograft techniques were used to assess proliferation, apoptosis, chemotaxis, and tumorigenicity of EsC cells expressing either wtTERT or TERT variants. Immunoprecipitation, immunoblot, immunofluorescence, promoter-reporter and qRT-PCR techniques were used to evaluate interactions of TERT and several TERT variants with BRG-1 and β-catenin, and to assess expression of cytoskeletal proteins, and cell signaling. Fluorescence in-situ hybridization and spectral karyotyping techniques were used to examine telomere length and chromosomal stability.ResultsSequencing analysis revealed one deletion involving TERC (TERC del 341-360), and two non-synonymous TERT variants [A279T (2 homozygous, 9 heterozygous); A1062T (4 heterozygous)]. The minor allele frequency of the A279T variant was five-fold higher in EsC patients compared to healthy blood donors (p<0.01). Relative to wtTERT, A279T decreased telomere length, destabilized TERT-BRG-1-β-catenin complex, markedly depleted β-catenin, and down-regulated canonical Wnt signaling in cancer cells; these phenomena coincided with decreased proliferation, depletion of additional cytoskeletal proteins, impaired chemotaxis, increased chemosensitivity, and significantly decreased tumorigenicity of EsC cells. A279T expression significantly increased chromosomal aberrations in mouse embryonic fibroblasts (MEFs) following Zeocin™ exposure, as well as Li Fraumeni fibroblasts in the absence of pharmacologically-induced DNA damage.ConclusionsA279T induces telomere dysfunction and inhibits non-canonical telomerase activity in esophageal cancer cells. These findings warrant further analysis of A279T expression in esophageal cancers and premalignant esophageal lesions.

Intraventricular meningiomas frequently harbor NF2 mutations but lack common genetic alterations in TRAF7, AKT1, SMO, KLF4, PIK3CA, and TERT

“…Finally, the TERT A279T mutation was found in our IVM cohort, which deviates from the previously reported TERT mutations in meningiomas (C228T and C250T) [46]. Functional data in esophageal cancer cells overexpressing TERT A279T induced telomere dysfunction but interestingly decreased proliferation of these cells [57]. In one WHO°II and its corresponding recurrent tumor, the already known driver mutation SMARCB1 R377H was detected [6, 52].…”

Characterization of genomic changes in the cervical pre-cancerous lesions and tumors induced by different types of human papillomaviruses

“…This deletion is common in glioblastoma tumors [5], breast cancer [3], lung cancer [20], colorectal cancer [4]. The deleted region contained UBE4B gene which is related with the rapid degradation of the product of tumor suppressor gene p53 [23,25]. Deletion in our case shows the direct link between tumorigenesis and deletion of this gene.…”

“…Despite the damage caused by the oncoviral proteins, CC is a rare complication of the viral infection because most infections are transient and do not evolve into neoplastic lesions. Although 95 % of the patients with precancerous lesions harbor HPV, only a small fraction of the cases eventually progress to invasive cancer [25]. On average, it takes 12-15 years before a persistent HPV infection may, via the premalignant stages of cervical intraepithelial neoplastic lesions (CIN), lead to CC.…”

TERT and TERC mutations detected in cryptic dyskeratosis congenita suppress telomerase activity

“…That finding and our observation that telomerase activity is maintained despite the mutation suggest the TERC c.73G>C mutation is also not causative for DKC. However, it is presumed that the TERT variant, which is located in nonessential linker regions in the N‐terminus of TERT protein, may destabilize interactions of TERT with other telomerase complex proteins and impair chromosomal capping by shelterin proteins . Moreover, the fact that Saos‐2 cells correct telomere length through ALT rather than telomerase activity indicates that telomerase activity does not account entirely for telomere length regulation.…”

“…However, it is presumed that the TERT variant, which is located in nonessential linker regions in the N-terminus of TERT protein, may destabilize interactions of TERT with other telomerase complex proteins and impair chromosomal capping by shelterin proteins. 27,28 Moreover, the fact that Saos-2 cells correct telomere length through ALT rather than telomerase activity indicates that telomerase activity does not account entirely for telomere length regulation. Consequently, it cannot be completely excluded that these gene mutations contribute to the pathogenesis of DKC by impairing a separate telomere regulatory mechanism.…”