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研究発表を行った学会；
・Cold Spring Harbor Laboratory (Retroviruses)
　２０１１年５月２３日〜２８日（New York, USA）

タイトル；COASSEMBLY OF HERV-K GAG WITH HIV-1 GAG.

発表者；門出　和精　氏
　　　（熊本大学　大学院生命科学研究部　感染防御学分野）
Abstract；
Human endogenous retrovirus (HERV) sequence comprises approximately 8% of human DNA. Although almost all HERV genomes seem to lack the intact open reading frames (ORFs) and are therefore likely defective in replication, some of them such as HERV-K113, which is known to have complete ORFs for all viral proteins, could be expressed as a fully functional virus. Previously, it was reported that HIV-1 infection enhances the HERV-K expression. Thus, it is possible that overexpression of HERV-K Gag driven by HIV-1 infection might compete or cooperate with HIV-1 Gag during assembly and release of infectious virions.
In this study, we confirmed that transcription of HERV-K mRNA is up to 10 fold enhanced by HIV-1 infection in Jurkat T cells. However such induction was not seen in HeLa cells. To investigate whether the HIV-1 Gag assembly and release is affected by overexpression of HERV-K Gag, we examined the HIV-1 assembly in HeLa cells cotransfected with both HIV-1 molecular clone pNL4-3 and CMV-promoter-driven HERV-KCON (a kind gift from Dr. Bieniasz). The release efficiency of HIV-1 Gag was 2 fold reduced upon overexpression of HERV-KCON Gag. Interestingly, HERV-KCON Gag colocalized with HIV-1 Gag at the plasma membrane. Furthermore, HERV-KCON Gag was copackaged with HIV-1 Gag into the virions and was processed by HIV-1 protease in virions. In addition, our preliminary coimmunoprecipitation data showed that HIV-1 Gag precursor protein binds to HERV-KCON Gag precursor protein.
Both membrane binding and RNA are important for Gag multimerization and thus could facilitate co-assembly of different retroviral Gag proteins. Indeed, when nonmyristoylated HERV-KCON Gag was coexpressed with HIV-1 Gag, HIV-1 Gag did not rescue the membrane binding of nonmyristoylated HERV-KCON Gag. This result indicates that the membrane binding of HERV-KCON Gag is essential for copackaging of HIV-1 Gag and HERV-K Gag into virions. To investigate whether NC-RNA interaction is important for Gag heteromultimerization at the plasma membrane, we analyzed the behavior of HERV-K Gag/delNC in HIV-1-expressing cells. We found that HERV-K Gag NC domain was required for colocalization, copackaging and interaction between HERV-KCON Gag and HIV-1 Gag. These results support that HIV-1 Gag heteromultimerizes with HERV-K Gag at the plasma membrane presumably through NC-RNA interaction. Intriguingly, overexpression of HERV-K Gag reduced not only HIV-1 release efficiency but also HIV-1 infectivity. Altogether, these results suggest that HERV-K Gag modulates the HIV-1 assembly and infectivity in human cells that express HERV-K.