title: A biochemical analysis linking APOBEC3A to disparate HIV-1 restriction and skin cancer.
abstract: Human deoxycytidine deaminase APOBEC3A (Apo3A) acts as an HIV-1 restriction factor in cells of myeloid lineage yet functions separately as a potent mutator for genomic DNA. Apo3A activity and C motif deamination specificity exhibit a striking dependence on pH that reflects these two distinct biological processes. Upon infection of macrophages, HIV-1 induces the formation of autophagosomes, and requires autophagosomes for replication, whereas inhibiting lysosomal fusion indicative of late stage autophagy. Here we show that Apo3A has optimal activity and a strict 5'-YYCR motif specificity in the pH 5.8-6.1 range, characteristic of enclosed autophagosomal membrane compartments, and reflective of the mutation pattern of HIV-1. In contrast to the high activity and narrow specificity of Apo3A at acid pH, a 13-30-fold reduction in specific activity is accompanied by relaxed C deamination specificity at pH 7.4-8. Notably, Apo3A is also expressed in keratinocytes, and is up-regulated in skin lesions. At pH 7.9, we show that Apo3A generates transcription-dependent CC → TT tandem mutations on the non-transcribed strand, a hallmark signature of skin cancer. The biochemical data taken in conjunction with the biological up-regulation of Apo3A in skin lesions suggests that enzyme-catalyzed deaminations at adjacent C sites followed by normal replication generating CC → TT mutations provides an alternative molecular basis for the initiation events in skin cancer in contrast to well established pathways in which CC dimers formed in response to UV radiation either undergo nonenzymatic spontaneous deaminations or aberrant replication.
authors: From the Departments of Biological Sciences and Chemistry, Molecular and Computational Biology Section, University of Southern California, Los Angeles, California 90089-2910.
authors: Phuong
authors: P
authors: Pham
authors: Alice
authors: A
authors: Landolph
authors: Carlos
authors: C
authors: Mendez
authors: Nancy
authors: N
authors: Li
authors: Myron F
authors: MF
authors: Goodman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016880:Anisotropy; D001483:Base Sequence; D003564:Cytidine Deaminase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005470:Fluorometry; D015497:HIV-1 / Q000235:genetics / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015603:Keratinocytes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism / Q000821:virology; D009154:Mutation; D059372:Nucleotide Motifs / Q000235:genetics; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D061987:Sf9 Cells; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D015854:Up-Regulation
chemical_list: D004277:DNA, Single-Stranded; D011506:Proteins; C121399:APOBEC3A protein, human; D003564:Cytidine Deaminase
keywords: APOBEC; DNA Damage; Deoxycytidine Deaminase; HIV-1; Mutagenesis; Myeloid Cell; Nucleic Acid Enzymology; Skin Cancer
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