Cytidine Deaminases APOBEC3G and APOBEC3F Interact with Human Immunodeficiency Virus Type 1 Integrase and Inhibit Proviral DNA Formation

Abstract

APOBEC3G (A3G) is a single-stranded DNA cytidine deaminase that targets retroviral minus-strand DNA and has potent antiviral activity against diverse retroviruses. However, the mechanisms of A3G antiviral functions are incompletely understood. Here we demonstrate that A3G, A3F, and, to a lesser extent, the noncatalytic A3GC291S block human immunodeficiency virus type 1 (HIV-1) replication by interfering with proviral DNA formation. In HIV-1 virions, A3G interacted with HIV-1 integrase and nucleocapsid, key viral factors for reverse transcription and integration. Unlike A3G, the weak antiviral A3C cytidine deaminase did not interact with either of these factors and did not affect viral reverse transcription or proviral DNA formation. Thus, multiple steps of the HIV-1 replication cycle, most noticeably the formation of proviral DNA, are inhibited by both cytidine deamination-dependent and -independent mechanisms.

Enzymatically Active APOBEC3G Is Required for Efficient Inhibition of Human Immunodeficiency Virus Type 1

“…Some of these effects do not require catalytically active APO3G (19,22), and several reports suggested that deaminase-defective APO3G and APO3F have antiviral activity when transiently coexpressed with HIV-1 in 293T cells (3,12,28,35). Our own data concerning the antiviral properties of the deaminase-defective APO3G C288S/C291A mutant supported these conclusions (30).…”

“…On the other hand, the single-round infectivity assay used in our studies is relatively insensitive to such APO3G-induced mutations since it requires only the production of functional Tat protein (31). Thus, the cytidine deaminase-induced loss of viral infectivity is more likely explained by effects on DNA stability or other effects such as the reported inhibition of tRNA-primed reverse transcription (9), inhibition of plus-strand transfer (26), or inhibition of integration (22,26).…”

“…In the absence of Vif, APO3G is efficiently packaged into HIV virions and inhibits virus replication. A number of studies reported that the presence of APO3G in the virus can result in hypermutation of the viral minus-strand cDNA during reverse transcription (11,18,23,24,42,45), inhibition of reverse transcription (9), tRNA annealing or tRNA processing (10, 26), DNA strand transfer (19, 26), or integration (22, 26).Some of these effects do not require catalytically active APO3G (19,22), and several reports suggested that deaminase-defective APO3G and APO3F have antiviral activity when transiently coexpressed with HIV-1 in 293T cells (3,12,28,35). Our own data concerning the antiviral properties of the deaminase-defective APO3G C288S/C291A mutant supported these conclusions (30).…”

“…In the absence of Vif, APO3G is efficiently packaged into HIV virions and inhibits virus replication. A number of studies reported that the presence of APO3G in the virus can result in hypermutation of the viral minus-strand cDNA during reverse transcription (11,18,23,24,42,45), inhibition of reverse transcription (9), tRNA annealing or tRNA processing (10,26), DNA strand transfer (19,26), or integration (22,26).…”

Restriction of Equine Infectious Anemia Virus by Equine APOBEC3 Cytidine Deaminases

“…Because of the difficulties in detecting eqA3-derived cytidine deamination in EIAV genomes, we studied the relevance of the zinc coordination domain for the antiviral activity. It has been reported that cytidine deamination is largely dispensable for the inhibition HIV-1 ⌬vif by human A3F and A3G (4,30,46,61). But controversially, several groups have reported a significant drop in inhibition observed when active-site mutants of human A3G were analyzed (8,9,22,23,56,75).…”