A high rate of polymerization during synthesis of mouse mammary tumor virus DNA alleviates hypermutation by APOBEC3 proteins

Publikationen als Autor:in / Herausgeber:in der Vetmeduni

Indik, Stanislav

Abstrakt

Retroviruses have evolved multiple means to counteract host restriction factors such as single-stranded DNA-specific deoxycytidine deaminases (APOBEC3s, A3s). These include exclusion of A3s from virions by an A3-unreactive nucleocapsid or expression of an A3-neutralizing protein (Vif, Bet). However, a number of retroviruses package A3s and do not encode apparent vif- or bet-like genes, yet they replicate in the presence of A3s. The mode by which they overcome deleterious restriction remains largely unknown. Here we show that the prototypic betaretrovirus, mouse mammary tumor virus (MMTV), packages similar amounts of A3s as HIV-1Vif, yet its proviruses carry a significantly lower level of A3-mediated deamination events than the lentivirus. The G-to-A mutation rate increases when the kinetics of reverse transcription is reduced by introducing a mutation (F120L) to the DNA polymerase domain of the MMTV reverse transcriptase (RT). A similar A3-sensitizing effect was observed when the exposure time of single-stranded DNA intermediates to A3s during reverse transcription was lengthened by reducing the dNTP concentration or by adding suboptimal concentrations of an RT inhibitor to infected cells. Thus, the MMTV RT has evolved to impede access of A3s to transiently exposed minus DNA strands during reverse transcription, thereby alleviating inhibition by A3 family members. A similar mechanism may be used by other retroviruses and retrotransposons to reduce deleterious effects of A3 proteins. Author summary Retroviruses have evolved multiple means for evading host restriction factors such as APOBEC3 proteins that lethally deaminate the intermediate product of reverse transcription reaction-single-stranded cDNA. Mouse mammary tumor virus (MMTV), although it does not encode an APOBEC3-neutralizing gene product and packages APOBEC3 proteins into the cores of virions, evades accumulation of the APOBEC3-mediated G-to-A mutations. Here, we show that a point mutation in the DNA polymerase domain of MMTV reverse transcriptase (F120L), which reduced the rate of DNA synthesis, increased APOBEC3-mediated mutation levels and, in turn, sensitivity to inhibition by APOBEC3 proteins. A similar APOBEC3 sensitizing effect was detected for cell culture conditions that slow down the rate of reverse transcription reaction such as decreased dNTP levels within target cells or the presence of sub-optimal, non-lethal concentrations of reverse transcriptase inhibitors. Thus, our results support the concept that MMTV has evolved reverse transcriptase to catalyze virus DNA synthesis with a rate that alleviates APOBEC3-mediated hypermutation of the virus replication intermediates. A similar mechanism may be used by other reverse transcriptase-containing viral pathogens to escape APOBEC3 innate immunity factors.

Dokumententyp

Originalarbeit

Open Access Type

Gold

DOI

10.1371/journal.ppat.1007533

PubMed ID

MEDLINE:30768644