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Tumor‐associated mutations in O 6 ‐methylguanine DNA‐methyltransferase (MGMT) reduce DNA repair functionality
Author(s) -
Lamb Kristy L.,
Liu Yanfeng,
Ishiguro Kimiko,
Kwon Youngho,
Paquet Nicolas,
Sartorelli Alan C.,
Sung Patrick,
Rockwell Sara,
Sweasy Joann B.
Publication year - 2014
Publication title -
molecular carcinogenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.254
H-Index - 97
eISSN - 1098-2744
pISSN - 0899-1987
DOI - 10.1002/mc.21964
Subject(s) - biology , methyltransferase , o 6 methylguanine dna methyltransferase , guanine , dna repair , dna damage , dna , dna methyltransferase , cancer research , mutation , microbiology and biotechnology , biochemistry , methylation , gene , nucleotide
MGMT is the primary vehicle for cellular removal of alkyl lesions from the O‐6 position of guanine and the O‐4 position of thymine. While key to the maintenance of genomic integrity, MGMT also removes damage induced by alkylating chemotherapies, inhibiting the efficacy of cancer treatment. Germline variants of human MGMT are well‐characterized, but somatic variants found in tumors were, prior to this work, uncharacterized. We found that MGMT G132R, from a human esophageal tumor, and MGMT G156C, from a human colorectal cancer cell line, are unable to rescue methyltransferase‐deficient Escherichia coli as well as wild type (WT) human MGMT after treatment with a methylating agent. Using pre‐steady state kinetics, we biochemically characterized these variants as having a reduced rate constant. G132R binds DNA containing an O 6 ‐methylguanine lesion half as tightly as WT MGMT, while G156C has a 40‐fold decrease in binding affinity for the same damaged DNA versus WT. Mammalian cells expressing either G132R or G156C are more sensitive to methylating agents than mammalian cells expressing WT MGMT. G132R is slightly resistant to O 6 ‐benzylguanine, an inhibitor of MGMT in clinical trials, while G156C is almost completely resistant to this inhibitor. The impared functionality of expressed variants G132R and G156C suggests that the presence of somatic variants of MGMT in a tumor could impact chemotherapeutic outcomes. © 2012 Wiley Periodicals, Inc.