Requirement of nef for HIV-1 infectivity is biased by the expression levels of Env in the virus-producing cells and CD4 in the target cells

The nef gene of human immunodeficiency virus type 1 (HIV-1) encodes a 27 to 34 kDa myristoylated protein, which enhances viral infectivity in a single-round infection assay. The level of Nef enhancement of HIV-1 infectivity depends on the viral strains, on the target cells, and on the cells used for propagating the viruses. In this study, we aimed at clarifying the molecular basis of these differences in the requirement for Nef. We found that the requirement for Nef was increased when we decreased the quantity of Env protein in the virus-producing cells or the quantity of CD4 in the target cells. Both the wild-type and Nef-defective HIV-1 viruses were propagated in 293T cells, which did not express any CD4; therefore, Nef-induced CD4 down-regulation did not explain this phenomenon. Moreover, we did not observe any increase in the viral entry or fusion activity of gp120env in the wild-type HIV-1 compared to that in the Nef-defective HIV-1. Thus, we propose that Env on the virion and CD4 on the target cells have inhibitory effects on the post-entry step of the HIV-1 replication cycle, and that Nef functions to counteract this negative effect.

Establishment of a MAGI-derived indicator cell line that detects the Nef enhancement of HIV-1 infectivity with high sensitivity

The Nef protein of the simian and human immunodeficiency viruses (SIV and HIV) is regarded as one of the critical determinants of the pathogenicity of HIV-1 in vivo. The positive effect of Nef on viral replication is examined most easily in vitro by the use of indicator cells such as HeLa-CD4-LTR-beta-gal cells (MAGI) or MAGIC5 cells, which are MAGI-derived, CCR5-expressing cells. However, Nef increases the infectivity of many HIV-1 strains no more than 10-fold in these indicator cells. It was noted that MAGI cells expressing a lower level of CD4 enabled us to discriminate more clearly between wild-type and Nef-defective virions. A MAGIC5-derived cell line, MAGNEF, which stably expressed a low level of CD4, was established. The infectivity of the Nef-defective HIV-1 NL4-3 strain was consistently less than one-twentieth of that of the wild type in MAGNEF cells. By using MAGNEF cells, it was shown that Nef enhanced the infectivity of a subtype C HIV-1, Indie-C1 strain, although the effect of Nef on Indie-C1 was significantly less than that on the subtype B strains NL4-3 and SF2. These results validate the versatility of MAGNEF cells for use in the simple and sensitive assay for the level of Nef dependence of various HIV-1 isolates.

Infectious DNA clone of HIV type 1 A/G recombinant (CRF02_AG) replicable in peripheral blood mononuclear cells

We constructed an infectious DNA clone of the HIV-1 A/G recombinant 97GH-AG2, which was isolated in Ghana in 1997 and was classified originally as subtype A. By phylogenetic and recombination breakpoint analyses, p97GH-AG2 was grouped in the circulating form of A/G recombinants (CRF02_AG) and was found to contain the least amount of subtype G-derived region among the known CRF02_AG HIV-1 DNAs. This result suggests that CRF02_AG may be a predominant form in Ghana. Virions produced by transfection of p97GH-AG2 into 293T cells grew in phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMCs). 97GH-AG2 also replicated efficiently in CCR5-expressing HeLa cells, MAGIC5, but only weakly in the parent MAGI cells, indicating that 97GH-AG2 uses mostly CCR5 as a coreceptor. Isolation of the first HIV-1 (CRF02_AG) DNA clone that replicates in PBMCs will accelerate the molecular analysis of this subtype.

Antimutagenicity of Tochu tea (an aqueous extract of Eucommia ulmoides leaves): 2. Suppressing effect of Tochu tea on the urine mutagenicity after ingestion of raw fish and cooked beef

The effect of Tochu tea, which is an aqueous extract of Eucommia ulmoides leaves and a popular-beverage in Japan, on the urine mutagenicity before and after ingestion of raw fish and cooked beef was studied using Salmonella typhimurium YG1024. Urines were collected from seven healthy, non-smoking Japanese women before and after ingestion of raw fish and cooked beef. In experiment 1,3 were in a control group and 4 were in a Tochu tea-drinking group (2000 ml per day). The mutagenicity of urine from the Tochu tea-drinking group was much lower. In experiment 2 the 7 women switched groups; the tea-drinking group became the control group, and the control group became the Tochu tea-drinking group. Again, the mutagenicity of urine collected from the Tochu tea-drinking group was much lower. These results suggest that the decrease in the mutagenicity of the urine from the Tochu tea-drinking group was due to the intake of Tochu tea, but not to individual differences. Thus, the ingestion of Tochu tea may reduce human exposure to dietary mutagens.