The human APOBEC3G (A3G) protein activity obstructs retrovirus infection by inducing mutations of guanosines to adenosines (G → A) in the viral DNA. These G → A mutations may disrupt the reading frames of the viral genes. It has been observed that A3G polymorphisms can affect the degree of G → A mutations and the disease progression. For example, one study showed that the nonsynonymous substitution H186R was linked to AIDS progression in African Americans. Other studies, however, found no association between A3G polymorphisms and progression to AIDS in Europeans or in Asians. The genetic structure of a host population likely affects the dynamics of HIV-1 infection. The AIDS infection in Brazil is unique because of the high incidence of isolates with an unusual motif (GWGR) at the V3 region of the env gene. Since the Brazilian population is a mix of Portuguese, native Amerindians, and Africans we aimed to explore the influence of A3G polymorphisms in HIV-1 infection in this heterogeneous host population. We analyzed seven loci polymorphisms of A3G in 400 HIV-1-infected individuals naive to drug therapy. Our findings indicated no significant influence of A3G polymorphisms on disease status. The exception was the SNP -571 (rs5757463) in which heterozygous individuals (C/G) and homozygous individuals (G/G) presented lower CD4(+) T cell counts compared to homozygous (C/C) individuals (Mann-Whitney test p-value = 0.0076). Furthermore, the loci diversity of A3G in Brazilians was similar to that of Europeans. Consequently, if there is any host factor that could be used to explain the peculiar subtype B HIV-1 infection in Brazil it is not associated with the innate immunity of the A3G gene.

BackgroundThe human APOBEC3G (A3G) protein activity is associated with innate immunity against HIV-1 by inducing high rates of guanosines to adenosines (G-to-A) mutations (viz., hypermutation) in the viral DNA. If hypermutation is not enough to disrupt the reading frames of viral genes, it may likely increase the HIV-1 diversity. To counteract host innate immunity HIV-1 encodes the Vif protein that binds A3G protein and form complexes to be degraded by cellular proteolysis.MethodsHere we studied the pattern of substitutions in the vif gene and its association with clinical status of HIV-1 infected individuals. To perform the study, unique vif gene sequences were generated from 400 antiretroviral-naïve individuals.ResultsThe codon pairs: 78–154, 85–154, 101–157, 105–157, and 105–176 of vif gene were associated with CD4+ T cell count lower than 500 cells per mm3. Some of these codons were located in the 81LGQGVSIEW89 region and within the BC-Box. We also identified codons under positive selection clustered in the N-terminal region of Vif protein, between 21WKSLVK26 and 40YRHHY44 regions (i.e., 31, 33, 37, 39), within the BC-Box (i.e., 155, 159) and the Cullin5-Box (i.e., 168) of vif gene. All these regions are involved in the Vif-induced degradation of A3G/F complexes and the N-terminal of Vif protein binds to viral and cellular RNA.ConclusionsAdaptive evolution of vif gene was mostly to optimize viral RNA binding and A3G/F recognition. Additionally, since there is not a fully resolved structure of the Vif protein, codon pairs associated with CD4+ T cell count may elucidate key regions that interact with host cell factors. Here we identified and discriminated codons under positive selection and codons under functional constraint in the vif gene of HIV-1.

Hypermutation alludes to an excessive number of specific guanine-to-adenine (G- >A) substitutions in proviral DNA and this phenomenon is attributed to the catalytic activity of cellular APOBECs. Population studies relating hypermutation and the progression of infection by human immunodeficiency virus type 1 (HIV-1) have been performed to elucidate the effect of hypermutation on the natural course of HIV-1 infection. However, the many different approaches employed to assess hypermutation in nucleotide sequences render the comparison of results difficult. This study selected 157 treatment-naive patients and sought to correlate the hypermutation level of the proviral sequences in clinical samples with demographic variables, HIV-1 RNA viral load, and the level of CD4(+) T cells. Nested touchdown polymerase chain reaction (PCR) was performed with specific primers to detect hypermutation in the region of HIV-1 integrase, and the amplified sequences were run in agarose gels with HA-Yellow. The analysis of gel migration patterns using the k-means clustering method was validated by its agreement with the results obtained with the software Hypermut. Hypermutation was found in 31.2% of the investigated samples, and a correlation was observed between higher hypermutation levels and higher viral load levels. These findings suggest a high frequency of hypermutation detection in a Brazilian cohort, which can reflect a particular characteristic of this population, but also can result from the method approach by aiming at hypermutation-sensitive sites. Furthermore, we found that hypermutation events are pervasive during HIV-1 infection as a consequence of high viral replication, reflecting its role during disease progression.

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