Cyclophilin A – Antizyme Fusion as a Potential HIV-1 Restriction Factor

Abstract

During the HIV-1 retroviral life cycle, endogenous cellular proteins serve to both promote and inhibit the retroviral reproductive cycle. Cyclophilin A (CypA) is one such protein that binds the viral capsid. The interaction between CypA and the capsid, especially in the target cell, has been demonstrated to be essential for efficient infection and progression through the HIV-1 reproductive cycle. However, other native proteins inhibit HIV-1 at various stages of the reproductive cycle. For example, TRIM5α catalyzes premature and accelerated capsid uncoating thereby blocking reverse transcription in certain species. Tetherin inhibits budding by tethering the virion to the cell and preventing release. Other proteins exploit a combination of interactions to assist in degradation. TRIMCyp fusions in certain primate species contain a TRIM5α domain fused to a Cyclophilin A domain. The combination results in capsid binding, premature uncoating, and prevention of reverse transcription. Here we attempt to exploit a similar interaction in the creation of a novel HIV-1 restriction factor by fusing CypA to the protein Antizyme-1. Endogenously, Antizyme plays a role in regulating polyamine levels by regulating levels of ornithine decarboxylase (ODC) by mediating ODC degradation via the 26S proteasome. We hypothesized that the combination of the capsid binding CypA domain and the proteasome associated Antizyme domain would result in premature degradation of the viral capsid resulting in reduced viral titer and infectivity. In contrast to our hypothesis, we found that expression of the CypA-Antizyme fusion did not affect viral titer or viral infectivity when expressed in both target and producer cell lines due in part to proteasome mediated degradation of our fusion construct. Despite the negative result, our data suggests future modifications that could be made to our construct to help evade cellular degradation mechanisms and eventually test the full therapeutic potential of the fusion.