Animal lectins play important roles in a variety of biological processes vi
a their recognition of glycoconjugates. Galectin-3 is a beta-galactoside-bi
nding lectin whose expression is associated with various pathological proce
sses including human T lymphotropic virus (HTLV)-I-infection of human T cel
l lines and human immunodeficiency virus (HIV) infection of T-lymphoblastic
Molt-3 cell line. In the case of HIV-infected cells, it has been suggested
that the increase in galectin-3 expression could be related to the express
ion of the viral regulatory gene tat. These results prompt us to perform mo
re extensive analyses of the relationship between galectin-3 and HIV-1 Tat
expressions. In this study, we found that Tat protein expression induces an
upregulation of galectin-3 in several human cell lines. In cotransfection
experiments, the 5'-regulatory sequences of the galectin-3 gene were signif
icantly upregulated by expression vectors encoding the Tat protein. Analysi
s performed with 5'-regulatory deleted sequences suggested that galectin-3
induction by Tat is dependent on activation of the Sp-1 binding transcripti
on factor.