Immunology Letters, 31 (1991) 11 - 14 Elsevier IMLET 01705

Identification of immunoglobulin recombination elements in human immunodeficiency virus type 1 envelope gene V. Veljkovi6 and R. Metla~ Laboratory of Multidisciplinary Research, Boris Kidri6 Institute, Belgrade, Yugoslavia (Received 28 December 1990; revision received 23 July 1991; accepted 25 July 1991)

1. Summary

Recently, it has been recognised that the amino acid motif VQL(N/V)ES is shared between the second conserved domain of human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gpl20) and the first framework (FWl) of human IgG heavy chain variable region (subgroup III) (VHIII). We have found that nucleotide sequence corresponding to this motif contains some recombination elements characteristic for the genes of human Ig heavy-chain variable region. The possible role of the Ig recombination elements in HIV-1 envelope gene variability, AIDS pathogenesis and vaccine design is discussed. 2. Introduction

The HIV-1 gpl20 represents the main antigen important for protection against the virus or infected cells, by both humoral and cell-mediated response. In spite of considerable sequence divergence among different HIV-1 isolates, the gpl20 molecules have retained their binding tropism for the CD4 receptor, as well as the ability to induce cytopathic effects in vitro (for review, see [1]). In the neutralisation of virus by antibodies, several epitopes of gpl20 may be involved, among which the epitopes belonging to the conserved doKey words: Human immunodeficiency virus; Immunoglobulin; Recombination element

Correspondence to: V. Veljkovi~, Laboratory for Multidisciplinary Research 180/2, Boris Kidri~ Institute, P.O. Box 522, 11001 Belgrade, Yugoslavia~

mains of the molecule are of interest. One such epitope was identified in the C-terminus of the second conserved domain (C2) of HIV-1 gpl20 (amino acids 254- 274) [2]. Unfortunately, in sera of infected individuals, the antibodies which bind to this epitope are not detected, even though it is immunogenic in heterologous systems [2]. For further vaccine design strategy, it is very important to answer the question why this epitope remains immunologically "silent" in humans. While investigating this region, we have recently identified the sequence motif common to HIV-1 gpl20 and some human proteins, most of which participate in the immune response and represent the members of the Ig gene superfamily [3]. Taking into account the possible role of this sequence motif in gpl20/CD4 recognition [4], as well as its high T cell reactivity [5], we suggest that this motif prevents activation of the neutralising epitope [3] situated within the C2 domain [2]. 3. Results and Discussion

The studies presented in this paper were designed to clarify the possible role of the amino acid motif VQL(N/V)ES, shared between the C2 domain of HIV-1 gpl20 and the FWl region of the human Vr~III, in viral life cycle and pathogenesis. Recently it has been reported that the nucleotide sequence GCTGGTGG, encoding the amino acids 2 - 3 (QLV) of this motif in VHIII, represents the Chi promoter, which has been shown to enhance generalised recombination in prokaryotes [6]. It is assumed that the role of Chi at this position in the Ig gene is to promote preferentially VHIII gene expres-

0165-2478 / 91 / $ 3.50 © 1991 Elsevier Science Publishers B.V. All rights reserved

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sion during the foetal B cell development [6]. On the other hand, the complete Chi octamer can be formed from the short sequences AGCT, T G G G and A G C T G G G G , identified in the switch DNA (S-DNA) recombination [7]. The DNA sequence encoding the peptide VQLNES within the second conserved domain of HIV-1 gpl20 contains a region with a large degree of homology to the Chi and S-DNA sequences (Fig. lb). It is important to note that this region of HIV-1 gpl20 gene is conserved among all HIV-1 isolates analysed. The gp 120 genes of certain HIV- 1 isolates (i.e., BH8) in this domain show a higher degree of sequence similarity (Fig. lc). Downstream from the putative Chi sequence in BH8 gpl20 gene, a heptamer sequence, CAGTCTG, has been located. Six of the seven bases match the consensus recombination signal C A C T G T G already found to be involved in V-(D)J recombination of the Ig gene (reviewed in [8] and [9]). A similar sequence exists at the same position in the gpl20 gene of all HIV-1 isolates. It has been a.

HIV-1

isolate

V

ARV-2

L

O

(0/E~

N

S

G T A C A G C T G A A T G A A T C T G

ItTLV-IIIB(BHIO) , LAVB~Iu

. . . . . . . . . . . . . . . . . . . .

BH8

HTLV- I I IRF (HAT3)

C C . . . . . . G - C C - C

. . . . . . . . . . . . .

. . . .

C

. . . . .

WMJI

. . . . .

NY5

. . . . . . . . . . . .

Z3

. . . . . . . .

CD-451

. . . . . . . . . . . .

CONSENSUS

G T A C A G C T G A A ' ' S ' T C T G

b.

E

. . . . . . . . . . . . .

< ......

T

A

. . . . . .

. . . . .

G A - -

G T A

FW1. . . . . .

-

. . . .

>

4

VH(III) gene

(cons.)

HIV-1 g p 1 2 0 g e n e

(cons.)

22

G T G C AG__CT G G _ T G_G A G T C T G

11

iiliil

iili

G T A C A G C T G A A • " • • T C T G

c. Vxlii gpl20(BHS)

G

T G

II

C_A

G_ C _ T . . ~

lilllll

G_ T

G

G

A

I

G

T

C

T

G

ilil

G T A C A G C T G G A C C A C T C T G

Fig. I. Homology between nucleotide sequences coding peptide VQL(N/V)ES in VHIII and HIV-I gpl20. The dash ( - ) below a nucleotide position denotes the Chi elements.

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speculated that genes other than Ig or T cell receptors containing this recombination signal could be the targets for the V-(D)-J recombinase system, as has been demonstrated for the haematopoietic transcription factor gene in acute lymphoblastic leukaemia [10, 11]. Within the VHIII gene, 260 nucleotides downstream from the Chi sequence, the second IgH specific recombination signal, TACTGTG, has been located [6]. The HIV-1 gpl20 gene, downstream of the Chi-like sequence at a similar distance ( 2 6 0 - 2 7 0 nucleotides, depending on the HIV-1 isolate), incorporates the homologous sequence TACTGTA [12], which represents a putative recombination signal. This sequence is conserved in all HIV-1 isolates. The nucleotide sequence between these two putative recombinant signals encodes the third hypervariable domain (V3), representing the dominant but strain-specific neutralising epitope of HIV-I gpl20 [13] (Fig. 2). This structural organisation suggests that this functionally important region of HIV-1 gpl20 gene may be involved in homologous recombination. As can be seen from Fig. 3, the consensus amino acid sequences of the V3 domain from 222 HIV-1 isolates [14] and the C-terminal region of VHIII (FW1, CDR1 and part of FW2) [15] also showed an unexpected degree of homology, although both consensus sequences involve hypervariable regions. According to the homology presented here between HIV-1 gpl20 and human VHIII, observed at the protein and DNA level, the following conclusions can be drawn. (i) The sequence homology between HIV-1 gpl20 and human Ig genes indicates the acquisition of host genes by the virus. This possible step in HIV-1 evolution represents the potential base for the escape mutant generation. (ii) The Chi sequence in HIV-1 gpl20 gene may be involved in the promotion of chromosomal rearrangement and the formation of aberrant immunoglobulins leading to inadequate humoral and cell-mediated immune response. The process of such abnormal recombination may also increase the frequency of B cell malignancies, which are observed in HIVinfected individuals. Recent results strongly confirm this possibility [16]. (iii) The vaccine based on the V3 loop of HIV-1 gpl20 (the main antigenic component in current approaches in anti-HIV vaccine design [17]) should be re-examined, because

V III II

FW1

CDR1

CDR2

FW2

I

FW3

I

/ r

260 bp . . . . . . . . .

It

II I I I I I I I gp120

>TACTGTG

I IIII

IIIIII

GTACAGCTC.~ACCACTCTG