Modulation of the activity of methyl binding domain protein 4 (MBD4/MED1) while processing iododeoxyuridine generated DNA mispairs

Abstract

DNA glycosylases function to remove endogenous and exogenous base damage

and thus contribute to the maintenance of genomic integrity. This function gains clinical

relevance when base mispairs introduced by chemotherapy or radiosensitizing drugs

become their substrate. This report describes the action of DNA glycosylases on the

mispairs generated by iododeoxyuridine (IUdR) – a radiosensitizer. A non-radioactive

fluorescent dye-based in vitro glycosylase assay was employed to quantitatively measure

the enzymatic activities of functionally related DNA glycosylases on IUdR generated

mispairs including G:IU and A:IU. Thymine DNA glycosylase (TDG) and methyl

binding domain protein 4 (MBD4/MED1) are found to act on G:IU (but not A:IU)

mispairs and are functionally complementary to each other. However, uracil DNA

glycosylase (UDG) does not show any activity on these mispairs. The methyl binding

domain of MBD4/MED1 was found to specifically inhibit the activity of MBD4/MED1

as well as the glycosylase domain, when the G:IU mispairs were located in a methylated

CpG context. However, inhibition of TDG activity on methylated G:IU mispairs by the

methyl binding domain was not observed.

This article is referred to by:

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