Inhibition of Human Endogenous Retrovirus-K10 Protease in Cell-free and Cell-based Assays

Abstract

A full-length and C-terminally truncated version of human endogenous retrovirus (HERV)-K10 protease were expressed in Escherichia coli and purified to homogeneity. Both versions of the protease efficiently processed HERV-K10 Gag polyprotein substrate. HERV-K10 Gag was also cleaved by human immunodeficiency virus, type 1 (HIV-1) protease, although at different sites. To identify compounds that could inhibit protein processing dependent on the HERV-K10 protease, a series of cyclic ureas that had previously been shown to inhibit HIV-1 protease was tested. Several symmetric bisamides acted as very potent inhibitors of both the truncated and full-length form of HERV-K10 protease, in subnanomolar or nanomolar range, respectively. One of the cyclic ureas, SD146, can inhibit the processing of in vitro translated HERV-K10 Gag polyprotein substrate by HERV-K10 protease. In addition, in virus-like particles isolated from the teratocarcinoma cell line NCCIT, there is significant accumulation of Gag and Gag-Pol precursors upon treatment with SD146, suggesting the compound efficiently blocks HERV-K Gag processing in cells. This is the first report of an inhibitor able to block cell-associated processing of Gag polypeptides of an endogenous retrovirus.

Human Endogenous Retrovirus K Gag Coassembles with HIV-1 Gag and Reduces the Release Efficiency and Infectivity of HIV-1

“…A previous report showed that HIV-1 protease is capable of cleaving HERV-K Gag in vitro (33). Therefore, if HERV-K Gag coassembles with HIV-1 virion components, HIV-1 protease is likely to cleave the HERV-K Gag in the same virion.…”

Human Endogenous Retrovirus Type K (HERV-K) Particles Package and Transmit HERV-K–Related Sequences

“…While no single human endogenous retrovirus sequence thus far identified in the genome encodes a complete infectious virus, the diverse HK2 loci in the human genome retain coding capacity for every functional retroviral protein (4,10,(28)(29)(30): the Gag protein, necessary for particle formation and release (31)(32)(33)(34)(35); the Pro protein, necessary for cleavage and maturation of viral proteins (35)(36)(37); the Pol protein, necessary for RNA-dependent DNA replication and integration (38)(39)(40)(41)(42); the accessory protein Rec, which exports unspliced viral RNA from the nucleus to the cytoplasm (43,44); and functional Env proteins (45). Recombination or trans-complementation between these proviruses could lead to the formation of viruses that would be able to package and transmit HK2 sequences (9,(46)(47)(48), as seen with endogenous retroviruses in mice (49)(50)(51).…”

ALSUntangled 45: Antiretrovirals

“…Additionally, the specific ARV used would need to have activity against the retrovirus targeted and the retrovirus would need to be actively producing infectious viral particles. If targeting HERV type K would be beneficial in PALS, which is still unknown, then a reasonable regimen might consist of two NRTIs and one INSTI given the data above (38)(39)(40)(41). The cost of the specific ARV regimen would depend on the drug(s) selected.…”

“…The current evidence, taken from in vitro studies, suggests that HERV type K is susceptible to most members of a class of ARVs called nucleoside reverse transcriptase inhibitors (NRTIs; 38,39), but is relatively resistant to ARVs from the class protease inhibitors (PIs; [38][39][40][41]. Evidence for in vitro efficacy of non-nucleoside reverse transcriptase inhibitors (NNRTIs) and integrase inhibitors (INSTIs) is mixed (38,39).…”