Functional Studies On A Potential HIV Fusion Inhibitor

The HIV-1envelope glycoprotein gp41plays a crucial role in the retroviral fusionprocess, and it is a very important target for membrane fusion inhibitor. Gp41can alsoregulate some cellular functions by interacting with host proteins. In the previous study,we screened human bone marrow cDNA library by a yeast-two-hybrid system, andidentified POB1as a potential binding protein to gp41. Considering the finding thatPOB1could inhibit the HIV-1mediated membrane fusion, we investigated the functionof POB1as being a potential membrane fusion inhibitor. The results showed that POB1exhibited inhibitory activity against HIV-1infection.We used a variety of biochemical techniques to verify the binding capacitybetween HIV-1gp41and POB1. The experimental results showed that the C-terminalhelical region (C60) of POB1bound strongly to the gp41six-helix bundle (6-HB), or tobe more precise, the N-terminal heptad repeat (NHR) of gp41. C60exhibited inhibitoryactivity against the HIV-1Env-mediated syncytium formation and virus infection, andthe half maximal inhibitory concentration (IC50) values were in the micromolar range.Unlike traditional membrane fusion inhibitors, C60did not block the gp416-HBformation, which implied that the inhibition mechanism of C60might not be the sameas other fusion inhibitors. The differences between these two inhibition mechanismsneed to be further explained and the further study on the mechanisms will be helpful toimprove our understanding of the viral membrane fusion process.It was reported that POB1was involved in the EGF/insulin-induced endocyticpathway. We cloned a new POB1homology, POB1(1-460), and HIV-1gp41could stillbe able to interact with POB1(1-460) in293T cells. We also observed significantenhancement of EGF internalization in A431cells and CHO cells expressing gp41, andthe uptake of HIV-1virions in the CD4-negative A431cells was also increased, whichmight help more HIV-1virions to enter into target cells to establish effective infection.HIV-1gp41could play a role in EGF signaling and recruit proteins in the endocyticpathway, such as POB1, epsin, to activate the process of endocytosis. The hypothesisneeds further experiments to confirm.