title: APOBEC3B and APOBEC3F inhibit L1 retrotransposition by a DNA deamination-independent mechanism.
abstract: The most common transposable genetic element in humans, long interspersed element 1 (L1), constitutes about 20% of the genome. The activity of L1 and related transposons such as Alu elements causes disease and contributes to speciation. Little is known about the cellular mechanisms that control their spread. We show that expression of human APOBEC3B or APOBEC3F decreased the rate of L1 retrotransposition by 5-10-fold. Expression of two related proteins, APOBEC3D or APOBEC3G, had little effect. The mechanism of L1 inhibition did not correlate with an obvious subcellular protein distribution as APOBEC3B appeared predominantly nuclear and APOBEC3F was mostly cytosolic. Two lines of evidence indicated that these APOBEC3 proteins use a deamination-independent mechanism to inhibit L1. First, a catalytically inactive APOBEC3B mutant maintained L1 inhibition activity. Second, cDNA strand-specific C --> T hypermutations were not detected among L1 elements that had replicated in the presence of APOBEC3B or APOBEC3F. In addition, lower levels of retrotransposed L1 DNA accumulated in the presence of APOBEC3B and APOBEC3F. Together, these data combined to suggest a model in which APOBEC3B or APOBEC3F provide a preintegration barrier to L1 retrotransposition. A particularly high level of APOBEC3F protein in human testes and an inverse correlation between L1 activity and APOBEC3 gene number suggest the relevance of this mechanism to mammals.
authors.affiliation: Department of Biochemistry, Molecular Biology and Biophysics, The Institute for Molecular Virology and The Beckman Center for Transposon Research, the University of Minnesota, Minneapolis, Minnesota 55455.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Stenglein
authors.affiliation: Department of Biochemistry, Molecular Biology and Biophysics, The Institute for Molecular Virology and The Beckman Center for Transposon Research, the University of Minnesota, Minneapolis, Minnesota 55455. Electronic address: rsh@umn.edu.
authors.forename: Reuben S
authors.initials: RS
authors.lastname: Harris
mesh_terms: D020087:Alu Elements / Q000235:genetics; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003564:Cytidine Deaminase / Q000378:metabolism* / Q000502:physiology; D043525:Cytosine Deaminase / Q000378:metabolism / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D004252:DNA Mutational Analysis / Q000379:methods; D018076:DNA, Complementary / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D020084:Long Interspersed Nucleotide Elements; D015778:Minor Histocompatibility Antigens; D009154:Mutation
chemical_list: D018076:DNA, Complementary; D015778:Minor Histocompatibility Antigens; C492906:APOBEC3F protein, human; D043525:Cytosine Deaminase; C495794:APOBEC3B protein, human; C578087:APOBEC3D protein, human; D003564:Cytidine Deaminase