Intron 4\u20135 hTERT DNA Hypermethylation in Merkel Cell Carcinoma: Frequency, Association with Other Clinico-pathological Features and Prognostic Relevance

Costantino Ricci,Francesca Ambrosi,Mauro Giulio Papotti,Luca Morandi,Alberto Righi,Stefano La Rosa,Francesca Maletta,Silvia Uccella,Angelo Gianluca Corradini,Dino Gibertoni,Sofia Asioli,Fausto Sessa,Claudio Agostinelli,Silvia Asioli

doi:10.1007/s12022-021-09669-y

Abstract

Merkel cell carcinoma (MCC) is an aggressive skin tumor with neuroendocrine differentiation, mainly affecting elderly population or immunocompromised individuals. As methylation of the human telomerase reverse transcriptase (mhTERT) has been shown to be a prognostic factor in different tumors, we investigated its role in MCC, in particular in intron 4–5 where rs10069690 has been mapped and recognized as a cancer susceptibility locus. DNA methylation analysis of hTERT gene was assessed retrospectively in a cohort of 69 MCC patients from the University of Bologna, University of Turin and University of Insubria. Overall mortality was evaluated with Kaplan-Meier curves and multivariable Royston-Parmar models. High levels of mhTERT (mhTERThigh) (HR = 2.500, p = 0.015) and p63 (HR = 2.659, p = 0.016) were the only two clinico-pathological features significantly associated with a higher overall mortality at the multivariate analysis. We did not find different levels of mhTERT between MCPyV (+) and (−) cases (21 vs 14, p = 0.554); furthermore, mhTERThigh was strongly associated with older age (80.5 vs 72 years, p = 0.026), no angioinvasion (40.7% vs 71.0%, p = 0.015), lower Ki67 (50 vs 70%, p = 0.005), and PD-L1 expressions in both tumor (0 vs 3%, p = 0.021) and immune cells (0 vs 10%, p = 0.002). mhTERT is a frequently involved epigenetic mechanism and a relevant prognostic factor in MCC. In addition, it belongs to the shared oncogenic pathways of MCC (MCPyV and UV-radiations) and it could be crucial, together with other epigenetic and genetic mechanisms as gene amplification, in determining the final levels of hTERT mRNA and telomerase activity in these patients.

Highlights

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor, predominantly affecting elderly population or immunocompromised individuals [1, 2]
Three main findings emerge from this study on methylation of the human telomerase reverse transcriptase (mhTERT) in MCC: 1. mhTERT is an epigenetic mechanism frequently activated in MCC, in particular in a locus mapped on intron 4–5 around the single-nucleotide polymorphism (SNP) variant rs10069690, which was previously described as correlated with several cancer types by genome-wide association studies [18]; Fig. 2 Kaplan-Meier survival curve shows a higher mortality in mhTERThigh group, with the curves diverging about 12 months after the surgery
2. mhTERT is an epigenetic mechanism involved in both MCPyV (+) and (−) MCC, but had a different distribution when compared with specific clinical-pathological features; 3. mhTERThigh was related to a higher mortality risk when adjusted for the main clinico-pathological features

Summary

Introduction

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor, predominantly affecting elderly population or immunocompromised individuals [1, 2]. Several authors investigated the most commonly altered genes and genetic pathways (TP53, RB1, PIK3CA, KIT, PDGFRA, PDCD1, chromosomal abnormalities, miRNAs, and many others) in MCC [5,6,7,8,9,10,11,12] They found that a number of oncogenes and tumor-suppressor genes, even if not mutated, are abnormally up- or down-regulated in MCC, through different epigenetic mechanisms [5,6,7,8,9,10,11,12]. Xie H. et al showed that there is a widespread hTERT mRNA expression in MCC and that higher hTERT mRNA levels are associated with a significantly shorter overall survival [9] They only investigated hTERT promoter mutations and amplifications and, as clarified by the same authors, the complex genetic and epigenetic regulation system of hTERT expression in MCC is still largely unknown [9]. Since mhTERT could be a relevant epigenetic mechanism in hTERT expression and an independent prognostic factor in several tumors, we investigated whether mhTERT is associated with overall mortality and with the most relevant clinical-pathological features in a series of MCC patients [9, 13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]

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Results

Discussion

Conclusion