Differential regulation by TGF-beta 1 and insulin of insulin-like growth factor binding protein-2 in IEC-6 cells.
The purposes of this study were to determine the regulation of insulin-like growth factor binding protein-2 (IGFBP-2) in IEC-6 cells by transforming growth factor-beta 1 (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 medium (CM) of IEC-6 cells in a dose-dependent fashion and that low doses of insulin (1.0 and 5.0 microgram/ml) also increased IGFBP levels in the CM of IEC-6 cells, but a high dose of insulin (10 micrograms/ml) depressed IGFBP release in the CM. Immunoblotting has shown that the IGFBP of 32 kDa 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 micrograms/ml). In addition, des (1-3) IGF-I (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-I. These findings suggest that the upregulation of IGFBP-2 by TGF-beta 1 occurs, at least in part, at the level of mRNA, whereas 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.
Guo
Y S
YS
Department of Surgery, University of Texas Medical Branch, Galveston 77555, USA.
Townsend
C M
CM
Jin
G F
GF
Beauchamp
R D
RD
Thompson
J C
JC
D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000302:isolation & purification / Q000378:metabolism; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D018971:Insulin-Like Growth Factor Binding Protein 2; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology; D007413:Intestinal Mucosa; D007583:Jejunum; D015347:RNA Probes; D051381:Rats; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D007328:Insulin; D018971:Insulin-Like Growth Factor Binding Protein 2; D015347:RNA Probes; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I