Inhibition of human immunodeficiency virus type 1 infection of human CD4+ T cells by microbial HSP70 and the peptide epitope 407-426

Abstract

Human immunodeficiency virus type 1 (HIV-1) virions contain heat shock proteins (HSP), but these proteins have received limited attention. The objectives of this study were to establish if the microbial 70-kDa HSP exerts an inhibitory effect on the HIV-1 infection of human CD4+ T cells, to identify an inhibitory peptide epitope within the sequence of HSP70, and to evaluate the kinetic features of any inhibitory activity. The results of these studies suggest that microbial HSP70 exerts dose-dependent inhibition on CCR5 (R5) strains of clades B, C, and D of HIV-1 infecting human CD4+ T cells. The site of the HIV-1-inhibitory function was identified within the C-terminal peptide binding domain of HSP70, and the function is expressed by the peptide epitope comprising amino acids 407 to 426. The mechanism of inhibition of HIV-1 infectivity by HSP70 is blocking of the CCR5 coreceptors directly and indirectly by inducing CC chemokines and APOBEC3G. The inhibitory effect of HSP70, its C-terminal fragment, or peptide 407-426 may make HSP70 useful as a microbicidal agent. A potentiating noncognate inhibition of HIV-1 infectivity by combined treatment with HSP70 and monoclonal or polyclonal antibody to CCR5 was demonstrated. This novel strategy may be utilized in therapeutic immunization against HIV-1 infection.

FIG. 1.

Dose-dependent inhibition of HIV-1. (A) Inhibition of the R5 (BaL) strain by HSP70 and p359-609 and the X4 (LAI) strain by HSP70. (B) Inhibition of the R5 and X4 strains by human HSP70 compared with that by microbial HSP70 (n, 3 or more experiments).

FIG. 2.

Effect of HSP70 (n = 6) and its C-terminal (aa 359 to 609; n = 5), N-terminal (aa 1 to 358; n = 3), and peptide binding (aa 359 to 494; n = 4) fragments on HIV-1. Shown are the levels of infectivity of HIV-1 R5 (BaL) (A) and HIV-1 X4 (LAI) (B) for CD4⁺ T cells separated from primary PBMC. Reverse transcriptase activity was measured and is expressed as counts per minute. *, P < 0.05. +, present; −, absent.

FIG. 3.

Effects of sequential treatment from 0 to 24 h with HSP70 (n = 7) and its C-terminal fragment (aa 359 to 609; n = 5). Shown are the levels of infectivity of HIV-1 R5 (BaL) (A) and HIV-1 X4 (LAI) (B) for CD4⁺ T cells separated from primary PBMC. *, P < 0.05. Reverse transcriptase was assayed on day 7, and reverse transcriptase activity is expressed as counts per minute.

FIG. 4.

Dose-dependent inhibition of the R5 strains of HIV-1 (BaL) in CD4⁺ T cells by p407-426 compared with inhibition by p457-496 (n = 3), p359-609 (n = 3), p359-609 from which aa 407 to 426 were deleted (Δ407-426; n = 2), and the control p367-386.

FIG. 5.

Inhibition of HIV-1. (A) Dose-dependent inhibition of the infectivity of the R5 strains of HIV-1 (BaL) for human CD4⁺ T cells (PM1 cell line) by HSP70 (20 μg/ml) and mAb to CCR5 alone and in combination. (B) Inhibition of R5 (BaL) and X4 (group O clinical isolate) strains of HIV-1 with HSP70 and polyclonal CCR5 antibodies alone and in combination. Ab, antibody.