Research Summaries

Bindong Liu
Assistant Professor

There are three major focuses of research in our laboratory. The first one is to understand the interaction between HIV-1 and host defense systems against HIV-1 replication. One system of defense involves a family of 10 proteins called APOBECs. APOBECs have cytidine deaminase activity, and three of the ten, APOBEC3G, 3F and 3DE, have strong anti-HIV activities. Despite this natural anti-HIV component of the immune system, infection and progression to AIDS are not stopped. We are interested in understanding the mechanism by which HIV-1 overcomes APOBEC

We have found that HIV encodes a small protein, termed Vif (viral infectious factor), to overcome the APOBECs’ antiviral activities by inducing their degradation through the proteosomal pathway. We also found that Cullin 5, a human ubiquitin E3 ligase, was hijacked by HIV Vif to induce APOBEC degradation. In this process, HIV Vif acts as an adaptor protein linking between Cul5 and APOBEC. We are particularly interested in the molecular interaction between Vif and APOBEC. We are going to identify the interaction domain between Vif and APOBEC, and study the molecular composition of their interaction.

To achieve this goal, we have identified a vif mutant which does not interact with Cullin 5. We will use this vif mutant as bait to co-immunoprecipitate APOBEC and identify the composition of this complex. We will also try to establish a Cullin 5 knockout cell-line to further study the function of the SCF Cullin 5-Vif complex in HIV-1 replication. We have reached the last step of construction of the targeting vector. Once the targeting vector is ready, we will transfect it into several cell lines, such as H9 and THP-1, to generate the knockout cell-line.

Meanwhile, we are also interested in looking for novel cellular factors that restrict HIV-1 replication. We recently identified a protein that shows the capability to restrict HIV-1 replication. In our preliminary study, this protein blocks viral replication at the viral protein translation or post-translation level while having no effect on CMV promoter-driven HIV-1 Gag expression. We will explore the mechanism in more detail. A better understanding of the interaction between host defense systems and HIV-1 replication will lead to the development of new targets for HIV medications.

More and more in vitro evidence has suggested that Apobec 3G is a potent host restriction factor against HIV-1 replication. It is uncertain whether Apobec 3G also influences HIV transmission and disease progression. HIV and AIDS disproportionately affect African Americans at a rate that is 10 times greater than the U.S. White population. Since 1996, more AIDS cases have occurred among African Americans than any other U.S racial/ethnic population. A recent study reported that one codon-changing variant, H186R in exon 4 of Apobec 3G, was polymorphic in African Americans. For African Americans, the variant allele 186R was strongly associated with a decline in CD4 T cells and was also associated with accelerated progression to AIDS-defining conditions. Our second focus is to determine whether this variation of Apobec 3G will influence HIV transmission and disease progression. We will be interested to look at the relationship between the variation of Apobec 3G and HIV transmission and disease progression among different racial groups through the study of Apobec 3G genetic variation and expression levels. It will assist in determining how to improve or develop new prevention or therapeutic approaches specific to ethnic and minority populations. We have established a real-time PCR system to measure the APOBEC expression level. Once the cohort is ready, we will evaluate the clinical samples.

Our third focus is to establish a robust viral culture system to replicate our candidate virus for HIV gene therapy. The candidate virus is a human non-pathogenic virus. It shares the same transmission pathway with HIV and specifically replicates in CD4+ T cell. These unique features render this virus a potential vector to deliver anti-HIV genes to CD4+ T cells, which are HIV’s natural target. However, the usage of the virus as a vector has been restricted by the lack of an efficient cell culture system, but we have successfully established a tissue culture system for long-term viral replication. This genetically engineered virus not only replicates in tissue culture but also has a high-level of expression for foreign genes, moving us closer to developing a vector for the purpose of HIV gene therapy.