title: Linking ATM Promoter Methylation to Cell Cycle Protein Expression in Brain Tumor Patients: Cellular Molecular Triangle Correlation in ATM Territory.
abstract: Ataxia telangiectasia mutated (ATM) is a key gene in DNA double-strand break (DSB), and therefore, most of its disabling genetic alterations play an important initiative role in many types of cancer. However, the exact role of ATM gene and its epigenetic alterations, especially promoter methylation in different grades of brain tumors, remains elusive. The current study was conducted to query possible correlations among methylation statue of ATM gene, ATM/ retinoblastoma (RB) protein expression, D1853N ATM polymorphism, telomere length (TL), and clinicopathological characteristics of various types of brain tumors. Isolated DNA from 30 fresh tissues was extracted from different types of brain tumors and two brain tissues from deceased normal healthy individuals. DNAs were treated with bisulfate sodium using DNA modification kit (Qiagen). Methylation-specific polymerase chain reaction (MSP-PCR) was implicated to determine the methylation status of treated DNA templates confirmed by promoter sequencing. Besides, the ATM and RB protein levels were determined by immunofluorescence (IF) assay using monoclonal mouse antihuman against ATM, P53, and RB proteins. To achieve an interactive correlation, the methylation data were statistically analyzed by considering TL and D1853N ATM polymorphism. More than 73% of the brain tumors were methylated in ATM gene promoter. There was strong correlation between ATM promoter methylation and its protein expression (p < 0.001). As a triangle, meaningful correlation was also found between methylated ATM promoter and ATM protein expression with D1853N ATM polymorphism (p = 0.01). ATM protein expression was not in line with RB protein expression while it was found to be significantly correlated with ATM promoter methylation (p = 0.01). There was significant correlation between TL neither with ATM promoter methylation nor with ATM protein expression nor with D1853N polymorphism. However, TL has shown strong correlation with patient's age and tumor grade (p = 0.01). Given the important role of cell cycle checkpoint proteins as well as RB and ATM in TL and cancer evolution, further assessment is warranted to shed more light on the pathway linking the telomere instability to tumor progression. High ATM methylation rate in brain tumor patients could open a new avenue toward early screening and cancer therapy.
authors.affiliation: Department of Medical Genetics, Tehran University of Medical Sciences, School of Medicine, Keshavarz Boulevard, Pour Sina Street, Tehran, Iran, mehdipor@tums.ac.ir.
authors.forename: P
authors.initials: P
authors.lastname: Mehdipour
authors.forename: F
authors.initials: F
authors.lastname: Karami
authors.forename: Firouzeh
authors.initials: F
authors.lastname: Javan
authors.forename: M
authors.initials: M
authors.lastname: Mehrazin
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D064007:Ataxia Telangiectasia Mutated Proteins / Q000235:genetics*; D001932:Brain Neoplasms / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D019394:Ki-67 Antigen / Q000378:metabolism; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011401:Promoter Regions, Genetic; D016160:Retinoblastoma Protein / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D059505:Telomere Homeostasis / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D019394:Ki-67 Antigen; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D064007:Ataxia Telangiectasia Mutated Proteins