Differential regulation by tgf-[beta]1 and insulin of insulin-like growth
factor binding protein -2 in iec-6 cells.
Guo, Yan-Shi, Courtney M. Townsend, Jr, Gui-Fang Jin, R. Daniel Beauchamp, and
James C. Thompson.
Departments of Surgery, and Microbiology, and Human Biological Chemistry
and Genetics, The University of Texas Medical Branch, Galveston, Texas
77555
APStracts 2:0010E, 1995.
The purposes of this study were to determine the regulation of IGFBP-2 in IEC
-6 cells by TGF-[beta]1 and insulin, and to determine whether IGFBP-2 mediated
the growth inhibitory action on the cells. Utilizing western ligand blot
analysis, we found that TGF-[beta]1 at concentrations of 0.5, 1.0 and 2 ng/ml
significantly increased levels of 32 KDa IGFBP in the conditioned media (CM)
of IEC-6 cells in a dose-dependent fashion and that low doses of insulin (1.0
and 5.0 [mu]g/ml) also increased IGFBP levels in the CM of IEC-6 cells, but
high dose of insulin (10 [mu]g/ml) depressed IGFBP release in the CM.
Immunobloting has shown that the IGFBP of 32KDa was IGFBP-2 and further
confirmed the above results. IGFBP-2 mRNA levels were stimulated by TGF-
[beta]1 (2.0 ng/ml) and suppressed by insulin (5.0 [mu]g/ml). In addition, des
(1-3) IGF-1 (50 ng/ml) and insulin stimulated the proliferation of IEC-6
cells. Anti-IGFBP-2 antibodies partially blocked the inhibitory role in IEC-6
cell growth evoked by Des (1-3) IGF-1. These findings suggest that the up-
regulation of IGFBP-2 by TGF-[beta]1 occurs, at least in part, at the level of
mRNA, while the regulation by insulin appears to be at a posttranslational
level, and that the TGF-[beta]1-stimulated production of IGFBP may contribute
to the growth -inhibitory action in intestinal epithelial cells.
Received 1 September 1994; accepted in final form 19 January 1995
APS Manuscript Number E359-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 February 1995.