Similar Regulation of Cell Surface Human T-Cell Leukemia Virus Type 1 (HTLV-1) Surface Binding Proteins in Cells Highly and Poorly Transduced by HTLV-1-Pseudotyped Virions

Abstract

Little is known about the requirements for human T-cell leukemia virus type 1 (HTLV-1) entry, including the identity of the cellular receptor(s).Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus which is the etiological agent of a severe lymphocyte neoplasia called adult T-cell leukemia/lymphoma (ATL) (53, 77) and a progressive neurological disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis (19,48). The virus is endemic in southern Japan, the Caribbean basin, Central and South America, and portions of West Africa. HTLV-1 and the closely related human T-cell leukemia virus type 2 (HTLV-2) are uncommon in the general populations of the United States and Europe. However, one recent study revealed that HTLV is prevalent in the United States among paid blood donors, African-American health care clinic patients, Amerindians, intravenous drug users, and patients with other-than-low-grade non-Hodgkin's lymphoma (52).ATL is a malignancy of CD4 ϩ T cells. It has been generally believed that the majority of the cells infected by HTLV-1 in vivo are CD4 ϩ T cells (30, 54). However, HTLV-1 can infect all subsets of human lymphocytes in vitro, and recent studies indicate that both CD4 ϩ and CD8 ϩ T cells serve as viral reservoirs in HTLV-1-associated myelopathy/tropical spastic paraparesis patients (42). Although capable of infecting a number of different cell types, HTLV-1 is poorly infectious in both primary cells and established cell lines in vitro.As for all retroviruses, entry of HTLV-1 into target cells is mediated by the envelope glycoproteins (Env), a surface glycoprotein (SU), and a transmembrane glycoprotein (TM). The HTLV-1 Env proteins are initially synthesized as precursor proteins, which are subsequently glycosylated and cleaved in the Golgi apparatus by a furin-like cellular protease to yield the SU (gp46) and the TM (gp21) glycoproteins. Following cleavage, the SU and the TM remain associated with each other through noncovalent interactions (51). As for other retroviruses, it is believed that the HTLV-1 SU glycoprotein specifically binds to a cellular receptor, inducing a conformational change in the SU-TM complex. This change activates a fusion domain within TM, allowing fusion of the viral and cellular membranes (5,9,10,37,51,55,56). Recent work using HTLV/ murine leukemia virus (MLV) envelope chimeras strongly suggests that the region of SU that interacts with the receptor is located within the N-terminal two-thirds of the protein (29). For HTLV-1, both SU and TM appear to play an additional role in a postfusion event critical for infectivity (11,28).The cellular receptor(s) for HTLV-1 have not yet been identified. Based on results from receptor interference assays, HTLV-1 is believed to share a common receptor with HTLV-2 and other primate T-cell leukemia/lymphoma viruses (64, 55). The gene encoding the receptor was mapped to chromosome 17 and further localized to 17q23. 2-25.3 (18, 35, 55), although later studies have questioned this assignment (27,47,67).A number of diffe...

Induction of Human T Cell Leukemia Virus Type I Receptors on Quiescent Naive T Lymphocytes by TGF-β

“…For each well in a six-well plate, 0.5 ml (5 ϫ 10 5 cells) were added along with 1 ml of viral supernatant, and cells were transduced using a modification of the spin infection method as described previously (20). The amount of viral particles present in each sample were quantified using a gag p24 ELISA (Zeptometrix).…”

“…The plasmids encoding HTLV-I Env (CMV-ENV-LTR) and the G protein of vesicular stomatitis virus (VSV)-G have been previously described (20). The plasmid encoding HTLV-II Env (CMV-ENV-LTR-II) was constructed as follows: a full-length clone of HTLV-II (pH6neo; gift of P. Green, Ohio State University, Columbus, OH) (48, 49) was digested with SphI and ClaI (5124 -7384) to generate a fragment that included the entire HTLV-II Env coding sequences.…”

“…Specific binding of HTSU-IgG to target cells was examined essentially as previously described (20) with the following modifications. Briefly, the lysates containing immunoadhesin (either HTSU-IgG or SUA-IgG) were centrifuged at 12,000 ϫ g for 1 min.…”

“…The cells were then sonicated twice, and the lysates were centrifuged at 800 ϫ g for 5 min. The clarified lysate was then aliquoted and stored at Ϫ80°C, and the concentration of immunoadhesins was determined by ELISA, as previously described (20).…”

“…293-T cells were transfected with either the plasmid vector encoding HTSU-IgG (HTSU-IgG/pSK100; Ref. 20) or a plasmid encoding a similar fusion protein (SUA-rIgG) containing the SU protein from the avian retrovirus ALSV-A (45). The latter was used as a negative control in all studies.…”