IGFBP-3 mediates TGF-β1-induced cell growth in human airway smooth muscle cells

Abstract

Both insulin-like growth factor binding protein-3 (IGFBP-3) and transforming growth factor-β (TGF-β) have been separately shown to have cell-specific growth-inhibiting or growth-potentiating effects. TGF-β stimulates IGFBP-3 mRNA and peptide expression in several cell types, and TGF-β-induced growth inhibition and apoptosis have been shown to be mediated through the induction of IGFBP-3. However, a link between the growth stimulatory effects of TGF-β and IGFBP-3-induction has not been shown. In this study, we investigated the role of IGFBP-3 in mediating TGF-β1-induced cell growth using human airway smooth muscle (ASM) cells as our model. TGF-β1 (1 ng/ml) treatment induced a 10- to 20-fold increase in the levels of expression of IGFBP-3 mRNA and protein. Addition of either IGFBP-3 or TGF-β1 to the growth medium resulted in an approximately twofold increase in cell proliferation. Coincubation of ASM cells with IGFBP-3 antisense (but not sense) oligomers as well as with an IGFBP-3 neutralizing antibody (but not with control IgG) blocked the growth induced by TGF-β1 ( P < 0.001). Several IGFBP-3-associated proteins were observed in ASM cell lysates, which may have a role in the cellular responses to IGFBP-3. These findings demonstrate that IGFBP-3 is capable of mediating the growth stimulatory effect of TGF-β in ASM cells.