Jpn. J. Infect. Dis., 52 (6), 251-252, 1999

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Laboratory and Epidemiology Communications

Integrase of Human Endogenous Retrovirus K-10 Supports the Replication of Replication-Incompetent Int- Human Immunodeficiency Virus Type 1 Mutant

Toshihiko Ogata, Nobuo Okui, Ryuta Sakuma, Noriko Kobayashi and Yoshihiro Kitamura*

Division of Molecular Genetics, National Institute of Infectious Diseases, Gakuen 4-7-1, Musashimurayama-shi, Tokyo 208-0011

Communicated by Hiroshi Yoshikura

(Accepted January 6, 1999)

The integration of proviral DNA is an essential step for retroviral replication and is mediated by a viral integrase (IN). In general, IN utilizes, as a donor substrate, long terminal repeats (LTR) of homologous origin but not of heterologous origin (1). However, in vitro studies suggested that human endogenous retrovirus (HERV) K-10 IN could utilize not only the homologous LTR but also human immunodeficiency virus type 1 (HIV-1) LTR as a substrate (4). This report demonstrates that Int-negative HIV-1 mutant replicated in cells simultaneously expressing HERV IN. This suggests that the HERV IN could utilize LTR of HIV-1, which is only distantly related to HERV (2).

Vpr-PC (protease cleavage sequence)-IN fusion protein has been shown to be incorporated into virions and cleaved into VprPC and IN during virion maturation (5,9). Therefore, we constructed a vector which expressed VprPC fused to IN of HERV (pC-VprPC/HERVIN) (Fig. 1). To determine whether HERV IN protein could be incorporated into HIV-1 virions, we transfected 293T cells (3) with pC-VprPC/IN together with pHQHY, an HIV-1 clone encoding non-functional mutated IN, which had base substitutions in the 12th and 16th histidine residues (6). Immunoblot analysis (Fig. 2) revealed the presence of HERV IN in HIVHQHY virions released from the transfected 293T cells, suggesting that HERV IN was actually incorporated into HIV-1 virions. Similarly, we prepared HIVHQHY virions that incorporated the intact IN of HIV-1LAI as a positive control and those which incorporated non-functional HERV IN, HIVIN(HHCCHERV) (amino acid residues 17-39 of HIV IN were replaced with 23 amino acid residues, VNAAGLKNKFDVTWKQAKDIVQH) as a negative control.

We compared infectivities of the virions incorporating various INs in MAGIC cells (7,8). The inocula contained the same amount of p24. The virions that incorporated the intact HERV IN actually produced blue colonies, and their estimated infectivity was about 3.7% of the infectivity of the virions incorporating the intact HIV-1 IN (Table). As the in vitro integration activity of HERV IN was about 10-30% of HIV-1 IN when HIV-1 LTR was used as a donor substrate (4), the value of 3.7% may be reasonable. Virions incorporating HIVINHHCCHERV showed no detectable infectivity. These experiments suggest that HERV IN mediated the integration reaction of HIV-1 LTR in vivo.

The above experiments may raise the possibility of an interaction between human endogenous retrovirus and HIV-1 during the replication process. In light of this, the development of integrase negative HIV mutant should be performed with caution.

We thank Dr. M. Tatsumi for MAGIC cells, and Drs. T. Kanda and K. Yoshiike for their encouragement. The work was supported by a grant from the Ministry of Education, Science, Sports and Culture of Japan.

REFERENCES

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* Corresponding author: Fax: +81-42-567-5632, E-mail:yochan@nih.go.jp


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