IGF-I INDUCES COLLAGEN AND IGFBP-5 MESSENGER-RNA 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 entero colitis by Northern analysis and in situ hybridization. IGFBP-5 mRNA w as increased 2.4 +/- 0.5-fold in inflamed rat colon compared with cont rols and was highly expressed in smooth muscle. Cultured rat intestina l 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 cu ltured smooth muscle cells. IGF-I induced a dose-and time-dependent in crease 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 tra nscriptional blockade. Cycloheximide abolished IGFBP-5 mRNA. In conclu sion, IGFBP-5 mRNA is expressed by intestinal smooth muscle and is inc reased during chronic inflammation. IGF-I increases IGFBP-5 and collag en mRNAs in intestinal smooth muscle cells.