Distinct profiles of TERT promoter mutations and telomerase expression in head and neck cancer and cervical carcinoma

Abstract

Two recurrent mutations (-124 G > A and -146 G > A) in the core promoter region of the human telomerase reverse transcriptase (TERT) gene create consensus binding sites for ETS transcription factors and cause increased TERT expression in several tumour types. We analyzed TERT promoter mutations and TERT mRNA levels in head and neck cancer, cervical carcinoma and cervical intraepithelial neoplasia (CIN) as well as in C-4I, CaSki, HeLa and SiHa cervical cell lines. Nucleotide sequence analysis of TERT promoter region showed that 33.3% of oral squamous cell carcinoma (SCC) and 16.8% of cervical SCC harboured mutually exclusive G to A transitions at nucleotide position -124 or -146. TERT promoter was mutated at nucleotide -146 (G > A) in SiHa cell line. Other nucleotide changes creating in some cases putative ETS binding sites were more frequent in oral SCC (26.7%) than in cervical carcinoma (4.8%). The frequency of mutations was independent of human papillomavirus (HPV) tumour status in both cervical and oral cancer. Expression of TERT gene was significantly higher in TERT promoter mutated (-124G > A or -146G > A) cervical SCC compared to not mutated SCC irrespective of HPV16 E6 and E7 levels. Such hot spot changes were not detected in oropharyngeal SCC, cervical adenocarcinoma and CIN lesions. Our results suggest that TERT promoter mutations play a relevant role in oral SCC as well as in cervical SCC, besides the already known effect of HPV16 E6 protein on TERT expression.

The Solo Play of TERT Promoter Mutations

“…While these are somatic mutations, a germline mutation at position −57A>C from the TSS has been identified in familial melanomas and showed similar effects [49]. All of these mutations have similar effects, increasing TERT expression~2-6 fold as measured through qRT-PCR, immunohistochemistry, TRAP, or reporter vectors in numerous cancer types, as outlined in Table 1 [37,50,[52][53][54][55][56][57][58][59][60][61][62][63][64][65]. This increased TERT expression maintains self-renewal potential and telomeres in both stem cells and terminally differentiated bladder cells, indicating that these mutations are sufficient to immortalize cells [66,67].…”

“…TERTp mutations were detected in cervical SCC (20.1%, range 4.5-21.8%) and HNSCC (22.5%, range 17-31.7%) [36,37]. These malignancies are often associated with high-risk-HPV16/18 E6 and E7 viral oncoproteins and with APOBEC mutations [125][126][127].…”

“…TERTp mutations have a notably higher prevalence in HPV-negative cervical and oral SCC. This gives distinct patterns of TERT reactivation through mutually exclusive mechanisms [36,37]. In cervical SCC, they are associated with higher TERT levels than HPV16/18-E6-positive tumors and with advanced cervical cancer [36,37].…”

“…This gives distinct patterns of TERT reactivation through mutually exclusive mechanisms [36,37]. In cervical SCC, they are associated with higher TERT levels than HPV16/18-E6-positive tumors and with advanced cervical cancer [36,37]. Broader studies are needed to evaluate the added value of screening for the molecular mechanism underlying TERT reactivation in cervical and oral SCC.…”

“…The TERT promoter (TERTp) contains binding sites for numerous transcriptional activators including Sp-1, c-Myc, Hypoxia Induced Factor (HIF), AP-2, β-catenin, NF-κB, E-twenty-six (Ets)/ternary complex factors (TCF) family members, and transcriptional repressors (Wilms' tumor (WT1), TP53, Nuclear Transcription Factor, X-Box Binding (NFX-1), Mad-1 and CCCTC binding factor (CTCF)) [3,4,9,[17][18][19][20][21]29]. TERT expression can be reactivated reactivated by copy number variants (CNV), TERT or TERTp structural variants, chromosomal rearrangements juxtaposing TERTp to enhancer elements, cellular and viral oncogenes such as Hepatitis B virus (HBV) X protein (HBx) or high-risk Human papillomavirus (HPV) 16 and HPV18 E6 oncoprotein, and, last but not least, mutations within TERTp (31% of TERT-expressing cancers) ( Figure 1A) [10,[30][31][32][33][34][35][36][37][38] (reviewed in [3,4,9,[18][19][20]39]). Increased TERTp methylation is typically recorded in >50% of TERT-expressing tumors and cell lines [10,[40][41][42][43][44][45][46][47].…”