title: MGMT gene silencing by promoter hypermethylation in gastric cancer in a high incidence area.
abstract: OBJECTIVE
  Inactivation of tumor suppressor and DNA repair genes by promoter hypermethylation does commonly occur in human cancers. O(6)-methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme that removes methyl groups as well as larger adducts at the O(6) position of guanine. In the absence of MGMT activity, O(6)-methylguanine mispairs with thymine during DNA replication, resulting in G:C to A:T transitions. Promoter hypermethylation of the MGMT gene has been observed in various cancers, including gastric cancer. Here, we aimed at assessing the promoter hypermethylation, mutation and expression status of the MGMT gene in patients from a geographic region with a high incidence of gastric cancer (Kashmir, North India) and to investigate their association with various clinicopathological characteristics.
  
  
  METHODS
  In this study 82 gastric cancer samples and adjacent normal tissues were included. Mutations in the MGMT gene were detected by single stranded conformational polymorphism (SSCP) analysis and direct sequencing. Methylation-specific polymerase chain reaction (MS-PCR) and Western blot analyses were performed to detect promoter hypermethylation and concomitant (loss of) expression of the MGMT gene.
  
  
  RESULTS
  Promoter hypermethylation of the MGMT gene was found in 52.44% (43 of 82) of the tumor samples and loss of MGMT protein expression was detected in 45.12% (37 of 82) of the tumor samples. Hypermethylation and loss of expression were significantly associated with higher tumor grades (moderately/poorly differentiated) (P < 0.05) and higher tumor stages (III/IV) (P < 0.05). In addition, MGMT hypermethylation and loss of expression were found to be significantly associated with high salt tea consumption (P < 0.05).
  
  
  CONCLUSIONS
  Our results indicate that MGMT promoter hypermethylation and concomitant loss of MGMT protein expression may play an important role in the development of gastric cancer in the Kashmiri population. High salt tea consumption may be a risk factor.
authors.affiliation: Department of Clinical Biochemistry, Sher-I-Kashmir Institute of Medical Sciences, Soura, Srinagar, Kashmir, 190011, India.
authors.forename: Adfar
authors.initials: A
authors.lastname: Yousuf
authors.forename: Mohammad Younis
authors.initials: MY
authors.lastname: Bhat
authors.forename: Arshad A
authors.initials: AA
authors.lastname: Pandith
authors.forename: Dil
authors.initials: D
authors.lastname: Afroze
authors.forename: Nighat P
authors.initials: NP
authors.lastname: Khan
authors.forename: Khursheed
authors.initials: K
authors.lastname: Alam
authors.forename: Parveen
authors.initials: P
authors.lastname: Shah
authors.forename: M Amin
authors.initials: MA
authors.lastname: Shah
authors.forename: Syed
authors.initials: S
authors.lastname: Mudassar
mesh_terms: D019175:DNA Methylation / Q000235:genetics*; D015254:DNA Modification Methylases / Q000235:genetics* / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D020868:Gene Silencing / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007194:India / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D018807:Polymorphism, Single-Stranded Conformational / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D012307:Risk Factors; D013274:Stomach Neoplasms / Q000453:epidemiology / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes