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.
Highlights
The human genome contains a large number of endogenous retroviral sequences that are virtually all highly defective because of multiple termination codons, deletions or the lack of a 5Ј long terminal repeat [1, 2]
The phenotype of human teratocarcinoma-derived retrovirus particles has been correlated with complex mRNA expression of human endogenous retroviruses (HERVs)-K sequences in those cells, reminiscent of the mRNA expression pattern observed after exogenous retrovirus infection with, for example, lenti- or spumavirus strains [8, 9]
Expression and Purification of HERV-K10 Proteases.—Two versions of HERV-K10 protease were expressed in E. coli
Summary
The human genome contains a large number of endogenous retroviral sequences that are virtually all highly defective because of multiple termination codons, deletions or the lack of a 5Ј long terminal repeat [1, 2]. HERV type K represents the biologically most active form of a variety of retroviral elements present in the human genome [1, 5]. Humans harbor several dozen proviral copies of HERV type K per haploid genome [4, 6, 7], some of which code for the characteristic retroviral proteins Gag, Pol, and Env [8, 9], recent studies raised a suggestion that no complete proviral copy of HERV-K exists [10, 11]; the issue remains to be clarified. HERV-K elements exhibit restricted cell type expression, observed mainly in germ cell tumors (including testicular teratocarcinoma cell lines) and their testicular precursor lesions [8, 12, 13]. The phenotype of human teratocarcinoma-derived retrovirus particles has been correlated with complex mRNA expression of HERV-K sequences in those cells, reminiscent of the mRNA expression pattern observed after exogenous retrovirus infection with, for example, lenti- or spumavirus strains [8, 9]
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