P. De Los Rios et Dj. Hill, Expression and release of insulin-like growth factor binding proteins in isolated epiphyseal growth plate chondrocytes from the ovine fetus, J CELL PHYS, 183(2), 2000, pp. 172-181
Insulin-like growth factor-ii (IGF-II) is an autocrine modulator of epiphys
eal chondrogenesis in the fetus. The cellular availability of ICFs are infl
uenced by the IGF-binding proteins (ICFBPs). In this study, we investigated
the control of expression and release of ICFBPs from isolated epiphyseal g
rowth plate chondrocytes from the ovine fetus by hormones and growth factor
s implicated in the chondrogenic process. Chondrocytes were isolated from t
he proliferative zone of the fetal ovine proximal tibial growth plate and m
aintained in monolayer culture at early passage number. Culture media condi
tioned by chondrocytes under basal conditions released ICFBPs of 24, 34, an
d 29 kDa, and a less abundant species of 39-43 kDa that were identified imm
unologically as IGFBP-4, IGFBP-2, IGFBP-5, and IGFBP-3, respectively. Messe
nger RNAs encoding each species were identified by Northern blot analysis w
ithin chondrocytes, as was mRNA encoding IGFBP-6. Exposure to ICF-I or IGF-
II (13 or 26 nM) caused an increase in expression and release of 1GFBP-3. T
he release of 1GFBP-2 and IGFBP-5 were also potentiated without changes to
steady state mRNA, and for IGFBP-5 this was due in part to a release from t
he cell membrane in the presence of ICF-II. Insulin (16.7 or 167 nM)selecti
vely increased mRNA and the release of IGFBP-3, while cortisol il or 5 mu M
) inhibited both mRNA and release of IGFBP-2 and ICFBP-5, Transforming grow
th factor-beta 1 (TGF-beta 1) (0.1 or 0.2 nM) increased the expression and
release of IGFBP-3. and caused an increase in mRNAs encoding IGFBP-2 and IC
FBP-5. Neither growth hormone (GH), Fibroblast growth factor-2, nor thyroxi
ne (T-4) had any effect on IGFBP expression or release. The results suggest
that IGFBP expression and release within the developing growth plate can b
e modulates by IGF-II and other trophic factors, thus controlling IGF avail
ability and action. (C) 2000 Wiley-Liss, Inc.