"In vivo, HIV replication is restricted to haematopoietic cells that express CD4 and either CCR5 or CXCR4. HIV therefore contrasts with other highly lymphotropic retroviruses, such as human T-lymophotropic virus type I, where virus receptors are expressed on diverse cell types (Weiss et al., 1985). For other retroviral receptors see the review by Sommerfelt (1999). "
[Show abstract][Hide abstract] ABSTRACT: Human immunodeficiency virus (HIV) exploits cell surface receptors to attach to and gain entry into cells. The HIV envelope spike glycoprotein on the surface of virus particles binds both CD4 and a seven-transmembrane coreceptor. These interactions trigger conformational changes in the envelope spike that induce fusion of viral and cellular membranes and entry of the viral core into the cell cytoplasm. Other cell surface receptors also interact with gp120 and aid attachment of virus particles. This review describes these receptors, their roles in HIV entry and their influence on cell tropism.
Journal of General Virology 09/2002; 83(Pt 8):1809-29. · 3.53 Impact Factor
"The viral proteins Gag, Pro, and Pol are expressed as precursor polyproteins Pr53 Gag , Pr76 Gag-Pro , and Pr160 Gag-Pro-Pol , respectively. The Env glycoprotein is synthesized as a 61-kDa precursor protein, which is subsequently glycosylated and cleaved into cell-surface (gp46) and transmembrane (gp21) proteins (Weiss et al., 1985). The expression of the pol gene requires two ribosomal frame-shiftings: one between gag and pro that generates Pr76 "
[Show abstract][Hide abstract] ABSTRACT: In this study, we examined the ability of human T-cell leukemia virus type I (HTLV-I) Gag and Gag-Pro to assemble immature virus-like particles (VLPs) and bud from insect and mammalian cells. Transmission electron microscopy of insect cells infected with a recombinant baculovirus carrying the entire gag gene revealed that Pr53(Gag) is targeted to the plasma membrane, where it extensively accumulates and forms electron-dense evaginations. However, no particles could be detected either inside the cells or in the culture supernatants. With the Gag-Pro-expressing construct, we observed HTLV-I-specific cytoplasmic proteolysis of the Gag precursor, but again no particle released in the culture supernatants. Transmission electron microscopic analysis of insect cells expressing Gag-Pro polyprotein revealed large vacuoles in the cytoplasm and no budding particles at the plasma membrane. In contrast, human immunodeficiency virus type 1 Gag polyprotein expressed in insect cells is able to release VLPs. These data showed that unlike other retroviruses, Pr53(Gag) is unable to be released as immature VLPs from insect cells. To determine whether the block in particle budding and release is due to an intrinsic property of Pr53(Gag) or the absence of essential cellular factors in insect cells, we expressed Gag and Gag-Pro polyproteins in human 293 cells. The results indicate that Pr53(Gag) and p24 capsid are released within particles into the culture supernatants of human 293 cells. We found that the myristylation of the N-terminal glycine residue is essential for Gag release. Altogether, these results strongly suggest that the proper assembly of HTLV-I particles is dependent on mammalian host cell factors.
"It is expressed on the surface of the infected cell and the virion as a complex of a 289-amino-acid, 46-kDa surface glycoprotein and a 176-amino-acid, 21-kDa transmembrane protein (TM). Analogous to other retroviruses, it is assumed that the surface glycoprotein binds to a cellular receptor, leading to conformational activation of the fusion sequence in the TM (Weiss et al., 1985). The nature of the cellular receptor and cellular entry is poorly understood. "
[Show abstract][Hide abstract] ABSTRACT: The receptor for human T-cell leukemia virus type 1 (HTLV-1) was found to be expressed on a broad range of cell lines derived from multiple species. Receptor expression was assessed using human immunodeficiency virus type 1 particles, pseudotyped with the HTLV-1 envelope glycoprotein, and expressing luciferase under the control of an SV40 enhancer and promoter. Infection by pseudotyped virus was blocked with neutralizing antibodies to HTLV-1, and infection was dependent on the presence of the cleavage and fusogenic sequences in the envelope protein precursor. Trypsin treatment of susceptible target lymphocytes reduced entry. Entry was partially resistant to ammonium chloride.
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