Methylcytosine and normal cytosine deamination by the foreign DNA restriction enzyme APOBEC3A.
Multiple studies have indicated that the TET oxidases and, more controversially, the activation-induced cytidine deaminase/APOBEC deaminases have the capacity to convert genomic DNA 5-methylcytosine (MeC) into altered nucleobases that provoke excision repair and culminate in the replacement of the original MeC with a normal cytosine (C). We show that human APOBEC3A (A3A) efficiently deaminates both MeC to thymine (T) and normal C to uracil (U) in single-stranded DNA substrates. In comparison, the related enzyme APOBEC3G (A3G) has undetectable MeC to T activity and 10-fold less C to U activity. Upon 100-fold induction of endogenous A3A by interferon, the MeC status of bulk chromosomal DNA is unaltered, whereas both MeC and C nucleobases in transfected plasmid DNA substrates are highly susceptible to editing. Knockdown experiments show that endogenous A3A is the source of both of these cellular DNA deaminase activities. This is the first evidence for nonchromosomal DNA MeC to T editing in human cells. These biochemical and cellular data combine to suggest a model in which the expanded substrate versatility of A3A may be an evolutionary adaptation that occurred to fortify its innate immune function in foreign DNA clearance by myeloid lineage cell types.
Department of Biochemistry, Molecular Biology and Biophysics, Institute for Molecular Virology, and Center for Genome Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Michael A
MA
Carpenter
Ming
M
Li
Anurag
A
Rathore
Lela
L
Lackey
Emily K
EK
Law
Allison M
AM
Land
Brandon
B
Leonard
Shivender M D
SM
Shandilya
Markus-Frederik
MF
Bohn
Celia A
CA
Schiffer
William L
WL
Brown
Reuben S
RS
Harris
D044503:5-Methylcytosine / Q000276:immunology / Q000378:metabolism*; D003564:Cytidine Deaminase / Q000276:immunology / Q000378:metabolism*; D004247:DNA / Q000276:immunology / Q000378:metabolism*; D003641:Deamination; D004790:Enzyme Induction / Q000187:drug effects / Q000276:immunology; D057809:HEK293 Cells; D006801:Humans; D007113:Immunity, Innate; D007372:Interferons / Q000276:immunology / Q000494:pharmacology; D010957:Plasmids / Q000276:immunology / Q000494:pharmacology; D011506:Proteins / Q000276:immunology / Q000378:metabolism*; D013941:Thymine / Q000276:immunology / Q000378:metabolism; D014498:Uracil / Q000276:immunology / Q000378:metabolism
D011506:Proteins; D014498:Uracil; D044503:5-Methylcytosine; D004247:DNA; D007372:Interferons; C121399:APOBEC3A protein, human; D003564:Cytidine Deaminase; D013941:Thymine