Details
| Original language | English |
|---|---|
| Pages (from-to) | 1110-1118 |
| Number of pages | 9 |
| Journal | CARCINOGENESIS |
| Volume | 42 |
| Issue number | 8 |
| Early online date | 11 Jun 2021 |
| Publication status | Published - 1 Aug 2021 |
| Externally published | Yes |
Abstract
The protein O6-methylguanine-DNA methyltransferase (MGMT) is able to repair the mutagenic O6-methylguanine (O6-MeG) adduct back to guanine. In this context, it may protect against colorectal cancer formation associated with N-nitroso compounds. Such compounds may be endogenously formed by nitrosylation of amino acids, which can give rise to mutagenic O6-MeG and O6-carboxymethylguanine (O6-CMG) adducts. It is well established that O6-MeG is repaired by MGMT. However, up to now, whether O6-CMG is repaired by this enzyme remains unresolved. Therefore, the aim of the present study was to analyze the fate of both types of O6-guanine adducts in the presence and absence of MGMT activity. To this end, MGMT activity was efficiently blocked by its chemical inhibitor O6-benzylguanine in human colon epithelial cells (HCECs). Exposure of cells to azaserine (AZA) caused significantly higher levels of both O6-MeG and O6-CMG adducts in MGMT-inhibited cells, with O6-CMG as the more abundant DNA lesion. Interestingly, MGMT inhibition did not result in higher levels of AZA-induced DNA strand breaks in spite of elevated DNA adduct levels. In contrast, MGMT inhibition significantly increased DNA strand break formation after exposure to temozolomide (TMZ), a drug that exclusively generates O6-MeG adducts. In line with this finding, the viability of the cells was moderately reduced by TMZ upon MGMT inhibition, whereas no clear effect was observed in cells treated with AZA. In conclusion, our study clearly shows that O6-CMG is repaired by MGMT in HCEC, thereby suggesting that MGMT might play an important role as a tumor suppressor in diet-mediated colorectal cancer.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Cancer Research
Sustainable Development Goals
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In: CARCINOGENESIS, Vol. 42, No. 8, 01.08.2021, p. 1110-1118.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Repair of O6-carboxymethylguanine adducts by O6-methylguanine-DNA methyltransferase in human colon epithelial cells
AU - Kostka, Tina
AU - Empl, Michael T
AU - Seiwert, Nina
AU - Geisen, Susanne M
AU - Hoffmann, Pascal
AU - Adam, Janine
AU - Seeger, Bettina
AU - Shay, Jerry W
AU - Christmann, Markus
AU - Sturla, Shana J
AU - Fahrer, Jörg
AU - Steinberg, Pablo
PY - 2021/8/1
Y1 - 2021/8/1
N2 - The protein O6-methylguanine-DNA methyltransferase (MGMT) is able to repair the mutagenic O6-methylguanine (O6-MeG) adduct back to guanine. In this context, it may protect against colorectal cancer formation associated with N-nitroso compounds. Such compounds may be endogenously formed by nitrosylation of amino acids, which can give rise to mutagenic O6-MeG and O6-carboxymethylguanine (O6-CMG) adducts. It is well established that O6-MeG is repaired by MGMT. However, up to now, whether O6-CMG is repaired by this enzyme remains unresolved. Therefore, the aim of the present study was to analyze the fate of both types of O6-guanine adducts in the presence and absence of MGMT activity. To this end, MGMT activity was efficiently blocked by its chemical inhibitor O6-benzylguanine in human colon epithelial cells (HCECs). Exposure of cells to azaserine (AZA) caused significantly higher levels of both O6-MeG and O6-CMG adducts in MGMT-inhibited cells, with O6-CMG as the more abundant DNA lesion. Interestingly, MGMT inhibition did not result in higher levels of AZA-induced DNA strand breaks in spite of elevated DNA adduct levels. In contrast, MGMT inhibition significantly increased DNA strand break formation after exposure to temozolomide (TMZ), a drug that exclusively generates O6-MeG adducts. In line with this finding, the viability of the cells was moderately reduced by TMZ upon MGMT inhibition, whereas no clear effect was observed in cells treated with AZA. In conclusion, our study clearly shows that O6-CMG is repaired by MGMT in HCEC, thereby suggesting that MGMT might play an important role as a tumor suppressor in diet-mediated colorectal cancer.
AB - The protein O6-methylguanine-DNA methyltransferase (MGMT) is able to repair the mutagenic O6-methylguanine (O6-MeG) adduct back to guanine. In this context, it may protect against colorectal cancer formation associated with N-nitroso compounds. Such compounds may be endogenously formed by nitrosylation of amino acids, which can give rise to mutagenic O6-MeG and O6-carboxymethylguanine (O6-CMG) adducts. It is well established that O6-MeG is repaired by MGMT. However, up to now, whether O6-CMG is repaired by this enzyme remains unresolved. Therefore, the aim of the present study was to analyze the fate of both types of O6-guanine adducts in the presence and absence of MGMT activity. To this end, MGMT activity was efficiently blocked by its chemical inhibitor O6-benzylguanine in human colon epithelial cells (HCECs). Exposure of cells to azaserine (AZA) caused significantly higher levels of both O6-MeG and O6-CMG adducts in MGMT-inhibited cells, with O6-CMG as the more abundant DNA lesion. Interestingly, MGMT inhibition did not result in higher levels of AZA-induced DNA strand breaks in spite of elevated DNA adduct levels. In contrast, MGMT inhibition significantly increased DNA strand break formation after exposure to temozolomide (TMZ), a drug that exclusively generates O6-MeG adducts. In line with this finding, the viability of the cells was moderately reduced by TMZ upon MGMT inhibition, whereas no clear effect was observed in cells treated with AZA. In conclusion, our study clearly shows that O6-CMG is repaired by MGMT in HCEC, thereby suggesting that MGMT might play an important role as a tumor suppressor in diet-mediated colorectal cancer.
UR - http://www.scopus.com/inward/record.url?scp=85114339000&partnerID=8YFLogxK
U2 - 10.1093/carcin/bgab049
DO - 10.1093/carcin/bgab049
M3 - Article
C2 - 34115837
VL - 42
SP - 1110
EP - 1118
JO - CARCINOGENESIS
JF - CARCINOGENESIS
SN - 0143-3334
IS - 8
ER -