Analysis of Functional Conservation in the Surface and Transmembrane Glycoprotein Subunits of Human T-Cell Leukemia Virus Type 1 (HTLV-1) and HTLV-2

Abstract

Human T-cell leukemia virus types 1 and 2 (HTLV-1 and HTLV-2) are closely related retroviruses with nucleotide sequences that are 65% identical. To determine whether their envelope glycoproteins function similarly and to define the molecular determinants of HTLV-2 envelope-mediated functions, we have used pseudotyped viruses and have introduced mutations into regions of the HTLV-2 glycoproteins homologous to those known to be important for HTLV-1 glycoprotein functions. The envelopes of the two viruses could be exchanged with no loss of infectivity, suggesting that the glycoproteins function in broadly similar ways. However, comparative analysis of the HTLV-1 and HTLV-2 glycoproteins showed subtle differences in the structure-function relationships of the two surface glycoprotein (SU) subunits, even though they recognize the same receptor. Indeed, mutations introduced at equivalent positions in the two SU glycoproteins resulted in different phenotypes in the two viruses. The scenario is the opposite for the transmembrane glycoprotein (TM) subunits, in which the functional domains of the two viruses are strictly conserved, confirming the involvement of the TM ectodomain in postfusion events required for full infectivity of the HTLVs. Thus, although they recognize the same receptor, the HTLV-1 and HTLV-2 SU subunits have slightly different ways of transducing the conformational information that primes a common fusion mechanism effected by similar TM subunits.

Early Assembly Step of a Retroviral Envelope Glycoprotein: Analysis Using a Dominant Negative Assay

“…The HTLV envelope expression vectors used in this study are the previously described plasmids CMV-ENV-1 ( Delamarre et al, 1997 ) and CMV-ENV-2 ( Rosenberg et al, 1998 ), which contain the respective HTLV-1 and HTLV-2 sequences corresponding to the env , tax , and rex genes, under the control of the simian cytomegalovirus (CMV) promoter. The CMV-ENVΔPvuII and CMV-ENVΔPmaCI constructs were used as the respective negative controls ( Delamarre et al, 1997 ; Rosenberg et al, 1998 ). The mutated constructs coding for HTLV-1 glycoproteins with single amino acid substitutions were described elsewhere ( Delamarre et al, 1997 ; Rosenberg et al, 1997 ).…”

“…Oligonucleotide-directed mutagenesis of the sequence encoding the SU portion of the HTLV-2 envelope protein was performed as described elsewhere ( Rosenberg et al, 1998 ). The constructs coding for HTLV-1 envelope proteins with truncations or deletions were generated using standard cloning techniques.…”

“…The quantitative assays used to evaluate syncytium formation elicited by the HTLV-1, HTLV-2, or HIV-1 envelopes have been described elsewhere ( Dragic et al, 1992 ; Delamarre et al, 1997 ; Rosenberg et al, 1998 ). In all these assays, the HIV-1 LTR-driven expression of β-galactosidase is transactivated by the Tat protein upon fusion of envelope-expressing cells with receptor-bearing indicator cells.…”

“…1 d (HTLV-2) or 2 d (HTLV-1) after transfection, 5 × 10 5 HeLa-Tat cells were added as indicator cells. After a 24-h coculture, the amount of β-galactosidase was evaluated by a chemiluminescence assay for detection of the activity of this enzyme in cell lysates (Galacto-Light; Tropix) with a luminometer (Lumat LB 9501; Berthold) ( Delamarre et al, 1997 ; Rosenberg et al, 1998 ). To assess the effect of the HTLV-1 glycoprotein mutants on syncytium formation induced by the wt HIV-1 envelope, the mutated HTLV-1 envelope constructs (2.25 μg) and the pMA243 plasmid (5 ng) were cotransfected into COS-1 cells seeded at 3 × 10 5 cells per 60-mm–diameter dish the previous day ( Cullen, 1987 ).…”

Molecular Study of HBZ and gp21 Human T Cell Leukemia Virus Type 1 Proteins Isolated from Different Clinical Profile Infected Individuals

“…5 Through characterization of neutralizing antibodies, peptides, and env mutants, it was possible to show that the gp21 harbors motifs that direct Env trafficking, membrane targeting, and virion incorporation. 6 More recently, the HTLV-1 bZIP factor gene (HBZ), which is encoded in the minus strand of the HTLV-1 genome, has been shown to be consistently expressed in adult T cell leukemia (ATL) cells and to be indispensable for the growth, survival, and proliferation of these cells. 7 As HBZ mRNA expression in TSP/HAM patients is well correlated with disease severity, it can play a critical role in disease development.…”