APOBEC3F Can Inhibit the Accumulation of HIV-1 Reverse Transcription Products in the Absence of Hypermutation

Abstract

APOBEC3F (apolipoprotein B mRNA-editing enzyme catalytic polypeptide 1-like protein 3F) is a cytidine deaminase that, like APOBEC3G, is able to restrict the replication of HIV-1/delta vif. Initial studies revealed high numbers of mutations in the cDNA of viruses produced in the presence of these proteins, suggesting that cytidine deamination underpinned the inhibition of infection. However, we have recently shown that catalytically inactive APOBEC3G proteins, derived through mutation of the C-terminal cytidine deaminase motif, still exert a substantial antiviral effect. Here, we have generated a panel of APOBEC3F mutant proteins and show that the C-terminal cytidine deaminase motif is essential for catalytic activity and that catalytic activity is not necessary for the antiviral effect of APOBEC3F. Furthermore, we demonstrate that the antiviral activities of wild-type and catalytically inactive APOBEC3F and APOBEC3G proteins correspond well with reductions in the accumulation of viral reverse transcription products. Additional comparisons between APOBEC3F and APOBEC3G suggest that the loss of deaminase activity is more detrimental to APOBEC3G function than to APOBEC3F function, as reflected by perturbations to the suppression of reverse transcript accumulation as well as antiviral activity. Taken together, these data suggest that both APOBEC3F and APOBEC3G are able to function as antiviral factors in the absence of cytidine deamination, that this editing-independent activity is an important aspect of APOBEC protein-mediated antiviral phenotypes, but that APOBEC3F may be a better model in which to study it.

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

“…In our own study, comparable inhibition of HIV-1 infectivity by wt and deaminase-defective APO3G required higher levels of the enzymatically inactive protein, leading us to conclude that wt APO3G had stronger antiviral potential than its deaminasedefective counterpart (30). Similar conclusions were drawn by Holmes et al (12). The requirement for high levels of virusassociated deaminase-defective APO3G for virus inhibition is reminiscent of one of our previous studies, in which we noted that the HIV-1 Vif protein, when packaged at supraphysiological levels into HIV-1 virions, had strong antiviral activity (2).…”

“…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).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).…”

Murine leukemia virus glycosylated Gag blocks apolipoprotein B editing complex 3 and cytosolic sensor access to the reverse transcription complex

“…The packaged APOBEC3 proteins inhibit infection in target cells by deaminating deoxycytidine residues on the DNA minus strand during reverse transcription, inducing hypermutation in newly synthesized HIV-1 DNA. APOBEC3 proteins also inhibit replication by cytidine deaminase-independent mechanism(s), such as blocking reverse transcription (18)(19)(20)(21). Vif binds several APOBEC3 proteins and targets them for ubiquitinylation and degradation in the proteasome in virus producer cells, thereby blocking the antiviral activity (22).…”

Restriction of Equine Infectious Anemia Virus by Equine APOBEC3 Cytidine Deaminases

“…Incorporated A3G specifically deaminates cytosine residues to uracil in growing singlestranded DNA during reverse transcription, leading to HIV genome degradation or hypermutation (5,25,39,48,49,98). More recent studies indicate that deaminase-independent mechanisms might also be involved in antiviral activity of A3 (4,27,28,30,54,61). The amount of encapsidated A3G in wild-type (wt) HIV-1 virions is dramatically reduced by a Vifdependent degradation via the ubiquitination-proteasome pathway (50,79,94,95).…”