Induction of galectin-1 expression by HTLV-I Tax and its impact on HTLV-I infectivity.
BACKGROUND
Cell-free Human T-cell Leukemia Virus type I (HTLV-I) virions are poorly infectious and cell-to-cell contact is often required to achieve infection. Other factors might thus importantly contribute in increasing infection by HTLV-I. Galectin-1 is a galactoside-binding lectin which is secreted by activated T lymphocytes. Several functions have been attributed to this protein including its capacity to increase cell-to-cell adhesion. Based on previous studies, we postulated that this protein could also accentuate HTLV-I infection.


RESULTS
Herein, we demonstrate that galectin-1 expression and release are higher in HTLV-I-infected T cells in comparison to uninfected T cells. Furthermore, galectin-1 expression was activated in various cell lines expressing the wild type viral Tax protein while this induction was minimal upon expression of NF-kappaB activation-defective TaxM22. Cotransfection of these Tax expression vectors with galectin-1 promoter-driven luciferase constructs confirmed that Tax upregulated galectin-1 promoter activity. However, a NF-kappaB-independent mechanism was strongly favoured in this induction of galectin-1 expression as no activation of the promoter was apparent in Jurkat cells treated with known NF-kappaB activators. Using HTLV-I envelope pseudotyped HIV-1 virions, galectin-1 was shown to increase infectivity. In addition, a co-culture assay with HTLV-I-infected cells also indicated an increase in cell fusion upon addition of galectin-1. This effect was not mediated by factors present in the supernatant of the HTLV-I-infected cells.


CONCLUSIONS
These data suggest that HTLV-I Tax increases galectin-1 expression and that this modulation could play an important role in HTLV-I infection by stabilizing both cell-to-cell and virus-cell interactions.
Gauthier
Sonia
S
Université du Québec à Montréal, Département des sciences biologiques, 2080 St-Urbain, Montréal, Québec, H2X 3X8, Canada. sonia.gauthier@crchul.ulaval.ca
Pelletier
Isabelle
I
Ouellet
Michel
M
Vargas
Amandine
A
Tremblay
Michel J
MJ
Sato
Sachiko
S
Barbeau
Benoit
B
D002448:Cell Adhesion; D002460:Cell Line; D018920:Coculture Techniques; D037483:Galectin 1 / Q000096:biosynthesis*; D016356:Gene Products, tax / Q000235:genetics / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000254:growth & development / Q000472:pathogenicity*; D006801:Humans; D016328:NF-kappa B / Q000172:deficiency; D013601:T-Lymphocytes / Q000821:virology*; D014774:Virulence
D037483:Galectin 1; D016356:Gene Products, tax; D016328:NF-kappa B; C514970:tax protein, Human T-lymphotrophic virus 1