Galectin 3 is an endogenous soluble beta-galactoside-specific lectin o
riginally identified and termed epsilon BP or IgE-binding protein in r
at basophilic leukemia cells, but its wide tissue distribution and the
multiple contexts in which it has been isolated have suggested that i
ts function may not be limited to IgE binding but may include a role i
n cell growth regulation and differentiation, neoplastic transformatio
n, and cell adhesion (Liu, 1990, Crit. Rev. Immunol., 10:289-306; Baro
ndes et al., 1994, J. Biol. Chem., 269:20807-20810). After immunoscree
ning of a lambda gt11 cDNA expression library made from bone-nodule fo
rming cultures of fetal rat calvaria (RC) cells with an antibody raise
d against osteoblastic tells (Turksen et al., 1992, J. Histochem. Cyto
chem., 40:1339-1352), three cDNA clones were isolated and sequenced; t
he sequence matched that of rat galectin 3. Galectin 3 mRNA was detect
ed in various fetal and adult rat tissues, including calvaria and cult
ured RC cells. In RC cells and the rat osteosarcoma cell line ROS 17/2
.8, galectin 3 mRNA expression increased with time in culture, in cont
rast to its behavior in fetal rat skin fibroblasts (RSF) in which its
expression decreased with time in culture. in a second rat osteosarcom
a line, UMR 106.01, galectin 3 mRNA was almost nondetectable. The synt
hetic glucocorticoid dexamethasone (Dex) enhanced galectin 3 expressio
n in RSF cell cultures, while 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-
3) had no significant effect. In contrast, Dex downregulated and 1,25(
OH)(2)D-3 upregulated galectin 3 expression in RC and ROS 17/2.8 cells
, especially at later time points in culture when expression of osteob
last-associated differentiation markers by these cell types is most ma
rked. Immunolabeling with an antibody against rat galectin 3 to identi
fy galectin 3 protein showed that cells labelled within both the ROS 1
7/2.8 and RC populations but with marked intercellular heterogeneity o
f intensity. Our data support the conclusion that galectin 3 is a prev
iously unrecognized product of osteoblastic cells, that galectin 3 mRN
A and protein expression increases with time in vitro concomitant with
other markers of osteogenesis, including formation of bone nodules an
d expression of osteoblast-associated markers such as alkaline phospha
tase, bone sialoprotein, and osteocalcin, and that its expression is r
egulated by hormones such as glucocorticoids and 1,25(OH)(2)D-3 that m
odulate other aspects of the osteoblast phenotype. (C) 1996 Wiley-Liss
, Inc.