Basic Science Award

As an obligatory intracellular parasite with limited genome size, retroviruses interact with both supportive and inhibitory host factors to complete their life cycle. Inhibitory factors could, in principle, intervene against the virus at every step of replication and are collectively called host restriction factors. Preliminary data indicated that human Piwil2 inhibited HIV replication at the step of HIV protein synthesis. Our objective is to understand the anti-HIV mechanism of Piwil2 and evaluate its physiological roles in cells or tissues with high levels of Piwil2. We will use different types of cells with either over-expressing or knockdown Piwil2 and measure their performance in HIV infection using pseudotyped HIV. Codon optimized GFP construct will be applied to test if Piwil2-related inhibition of protein synthesis is HIV-specific. The anti-HIV mechanism of Piwil2 is likely due to its interaction with tRNAs rather than piRNAs. Initial investigation will use electrophoretic mobility shift assays with tRNA as probe to see if Piwil2 binds to tRNA. Deep sequencing of RNAs bound to Piwil2 and small RNA array will be exploited to uncover associated RNA species that may be important in HIV inhibition. Then, the effect of Piwil2 on HIV replication will be evaluated in Piwil2-knockdown Jurkat and primary T cells. Further experiment aims to assess how Piwil2 responds to T cell activation and IFN stimuli. The length of this study is one year. Since levels of Piwil2 are also high in teratocarcinomas and embryonic tissues, Piwil2 could also inhibit maternal-fetal transmission of HIV. Our results could also reveal how Piwil2 renders tumor cells more anaplastic and metastatic.