Loss of 5'-Methylthioadenosine Phosphorylase (MTAP) is Frequent in High-Grade Gliomas; Nevertheless, it is Not Associated with Higher Tumor Aggressiveness.

Matias Melendez,Chris Jones,Maria Luisa Corcoll Spina,Marcela Nunes Rosa,Isabela Werneck da Cunha,Glaucia Noeli Maroso Hajj,Weder Pereira de Menezes,Carlos Clara,Rui Manuel Reis,Viviane Aline Oliveira Silva,Luciane Sussuchi da Silva,Izabela Natália Faria Gomes,Gisele Caravina Almeida,Adriana Cruvinel Carloni,Lucas Tadeu Bidinotto,Ana Laura Vieira Alves

doi:10.3390/cells9020492

Abstract

The 5’-methylthioadenosine phosphorylase (MTAP) gene is located in the chromosomal region 9p21. MTAP deletion is a frequent event in a wide variety of human cancers; however, its biological role in tumorigenesis remains unclear. The purpose of this study was to characterize the MTAP expression profile in a series of gliomas and to associate it with patients’ clinicopathological features. Moreover, we sought to evaluate, through glioma gene-edited cell lines, the biological impact of MTAP in gliomas. MTAP expression was evaluated in 507 glioma patients by immunohistochemistry (IHC), and the expression levels were associated with patients’ clinicopathological features. Furthermore, an in silico study was undertaken using genomic databases totalizing 350 samples. In glioma cell lines, MTAP was edited, and following MTAP overexpression and knockout (KO), a transcriptome analysis was performed by NanoString Pan-Cancer Pathways panel. Moreover, MTAP’s role in glioma cell proliferation, migration, and invasion was evaluated. Homozygous deletion of 9p21 locus was associated with a reduction of MTAP mRNA expression in the TCGA (The Cancer Genome Atlas) - glioblastoma dataset (p < 0.01). In addition, the loss of MTAP expression was markedly high in high-grade gliomas (46.6% of cases) determined by IHC and Western blotting (40% of evaluated cell lines). Reduced MTAP expression was associated with a better prognostic in the adult glioblastoma dataset (p < 0.001). Nine genes associated with five pathways were differentially expressed in MTAP-knockout (KO) cells, with six upregulated and three downregulated in MTAP. Analysis of cell proliferation, migration, and invasion did not show any significant differences between MTAP gene-edited and control cells. Our results integrating data from patients as well as in silico and in vitro models provide evidence towards the lack of strong biological importance of MTAP in gliomas. Despite the frequent loss of MTAP, it seems not to have a clinical impact in survival and does not act as a canonic tumor suppressor gene in gliomas.

Highlights

Gliomas represent the most common group of primary central nervous system (CNS) tumors [1].According to the World Health Organization (WHO), these tumors can be categorized in low-grade gliomas (LGG, WHO grades I and II) and high-grade gliomas (HGG, WHO grades III and IV) according to their histological and molecular features [2,3]
In order to understand the molecular mechanism underlying methylthioadenosine phosphorylase (MTAP) expression, we investigated the impact of copy number alteration (CNA) of 9p21 locus on MTAP mRNA expression levels in a The Cancer Genome Atlas (TCGA)-GBM dataset (n = 350)
Since MTAP regulation can occur by epigenetic mechanisms [27], we evaluated the association of MTAP mRNA expression and the methylation status in 283 samples from the TCGA-GBM dataset (Figure 1B)

Summary

Introduction

According to the World Health Organization (WHO), these tumors can be categorized in low-grade gliomas (LGG, WHO grades I and II) and high-grade gliomas (HGG, WHO grades III and IV) according to their histological and molecular features [2,3]. >90%), previously known as primary (de novo) GBM and exhibiting a short clinical history, and GBM IDH-mutant, called secondary GBM, which results from the malignant progression from lower-grade gliomas of diffuse (WHO grade II) or anaplastic (WHO grade III) astrocytomas [6,8] and is related to point mutations in IDH1/2 genes. In 2014, the International Society of Neuropathology recommended the support of molecular analysis for determining brain tumor entities [9] and, in 2016, the World Health Organization proposed the use of molecular features, including IDH mutation to GBM, in addition to histologic features in the tumor entities [3]. TERT promoter mutations have been found to be markedly high in primary GBMs

Objectives

Methods

Results

Conclusion