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.

Aberrant gene-specific DNA methylation signature analysis in cervical cancer

“…57 ATM protein belongs to PI3/PI4-kinase family and is an important cell cycle-checkpoint kinase reported as hypermethylated in human colorectal cancer cell lines, oral SCCs, breast cancers, and brain tumors. [58][59][60][61] In addition to this, methylation of ATM promoter is correlated with radiosensitivity in colorectal cancers. 59 FGF18 is a fibroblast growth factor family member possessing cell survival and mitogenic activities and is involved in cell growth, morphogenesis, tumor growth, and invasion by regulation of actin cytoskeleton, PI3K, and fibroblast growth factor receptor (FGFR) signaling.…”

ATM in breast and brain tumors: a comprehensive review

“…Furthermore, metastatic progression has been classified as a stepwise molecular alteration process of cancer development which requires three hits, D1853N, IVS38-63T>A, and IVS38-30A>G, occurring sequentially in astrocytes 152 ( Figure 4 ). In addition, Mehdipour et al 67 found a triangular correlation between methylation of the ATM promoter and protein expression of ATM with the D1853N variant. Evaluation of the D1853N variant alongside other alterations in patients with breast cancer, particularly those with breast to brain metastases, could lead to development of appropriate clinical management approaches.…”

“…These observations are comparable with the high expression levels of p53 and ATM proteins in healthy individuals. Interestingly, low levels of ATM protein expression, together with clones of cells with low levels of Rb protein, indicate a harmonic expression pattern in astrocytoma tumors 67 . …”

“…The methylation pattern of the ATM promoter has been investigated in a few studies of different types of brain tumors 177,178 . For example, Mehdipour et al 67 found that more than 73% of brain tumors exhibit methylation of the ATM promoter. A strong correlation between ATM promoter methylation and its protein expression has also been established.…”

Ability to downregulate the level of cyclin-dependent kinase inhibitor p27Kip1 after DNA damage is retained in chronic lymphocytic leukemia cells with functional ATM/p53 signaling pathway

“…Interestingly, four samples with wt ATM allele had either none (P12, P13, P16) or borderline (P15) levels of p53-Ser15 phosphorylation after IR, suggesting defective ATM/p53 pathway. Whether this apparent nonfunctionality of ATM in wt/del ATM samples is due to an involvement of other factors impacting on the expression and activity of ATM [12] or due to a possible epigenetic silencing of ATM expression known in various types of cancer [13] remains to be determined.…”