IGF-I induces collagen and IGFBP-5 mRNA in rat intestinal smooth muscle

Insulin-like growth factor (IGF) binding protein 5 (IGFBP-5) mRNA was studied in intestines of rats with peptidoglycan-polysaccharide enterocolitis by Northern analysis and in situ hybridization. IGFBP-5 mRNA was increased 2.4 +/- 0.5-fold in inflamed rat colon compared with controls and was highly expressed in smooth muscle. Cultured rat intestinal smooth muscle cells were used to study the regulation of IGFBP-5 and type I collagen synthesis. IGF-I (100 ng/ml) increased IGFBP-5 mRNA(1.9 +/- 0.1-fold) and collagen type al(I) mRNA (1.6 +/- 0.2-fold) in cultured smooth muscle cells. IGF-I induced a dose-and time-dependent increase in IGFBP-5 in conditioned medium by Western ligand blot and by immunoblot. IGF-I did not affect the IGFBP-5 mRNA decay rate after transcriptional blockade. Cycloheximide abolished IGFBP-5 mRNA. In conclusion, IGFBP-5 mRNA is expressed by intestinal smooth muscle and is increased during chronic inflammation. IGF-I increases IGFBP-5 and collagen mRNAs in intestinal smooth muscle cells.