The Pro-Fibrotic Factor IGFBP-5 Induces Lung Fibroblast and Mononuclear Cell Migration

Abstract

We have previously shown that insulin-like growth factor-binding protein-5 (IGFBP-5) is overexpressed in fibrotic lung tissues and that it induces production of extracellular matrix components such as collagen and fibronectin both in vitro and in vivo. We recently observed mononuclear cell infiltration in lung tissues of mice expressing IGFBP-5. We therefore examined the role of IGFBP-5 on the migration of immune cells. Migration assays demonstrated that IGFBP-5 induced migration of peripheral blood mononuclear cells (PBMCs) in a dose-dependent manner. Preferential migration of monocytes/macrophages, natural killer cells, and T cells was observed. Moreover, the CD4/CD8 ratio of migrating cells was significantly higher in vitro and in vivo in response to IGFBP-5. IGFBP-5 resulted in preferential migration of activated CD4 1 T cells and monocytes. Interestingly, IGFBP-5 also induced migration of primary human lung fibroblasts. Exogenous administration of IGFBP-5 induced activation of mitogen-activated protein kinase (MAPK) signaling cascade but not PI3K in PBMCs. IGFBP-5-induced migration was blocked by the MEK1/2 inhibitor U0126, suggesting that IGFBP-5-induced migration occurs via MAPK activation. Furthermore, monocytes treated with recombinant IGFBP-5 expressed the mesenchymal markers a-smooth muscle actin and fibronectin in vitro and in vivo, suggesting that IGFBP-5 can induce the transformation of monocytes into mesenchymal cells. Collectively, our results suggest that IGFBP-5 induces cell migration via MAPK-dependent and IGF-Iindependent mechanisms.

Defining the Disulfide Bonds of Insulin-like Growth Factor-binding Protein-5 by Tandem Mass Spectrometry with Electron Transfer Dissociation and Collision-induced Dissociation

“…Our results definitively identify 5 of 9 disulfide bonds in the protein, and determine that the other 4 linkages involve the four cysteines within the conserved GCGCCMTC motif (residues [32][33][34][35][36][37][38][39] in the N-terminal region of the protein.…”

The Fibrotic Phenotype Induced by IGFBP-5 Is Regulated by MAPK Activation and Egr-1-Dependent and -Independent Mechanisms

“…36 The role of MAPK activation as a mediator of IGFBP-5 effects is also supported by our recent findings demonstrating that IGFBP-5 triggers the migration of peripheral blood mononuclear cells in an IGF-I-independent MAPK-dependent manner. 37 Collectively, these observations suggest that the MAPK pathway is a convergent pathway for multiple mediators of fibrosis, including IGFBP-5.…”

“…We have recently reported IGFBP-5's chemoattractant activity for human peripheral blood mononuclear cells. 19,37 IGFBP-5 has also been shown to induce migration of mouse embryonic cells, 52 porcine vascular smooth muscle cells, 21 and rat glomerular mesengial cells. 53 We and others have shown that activation of MAPK and c-Raf also plays an important role in the regulation of cell migration.…”

Insulin-like growth factor binding proteins and mammary gland development

“…This would not be anticipated if they were both acting by inhibiting the actions of IGFs. ERK activation by IGFBP-5 has been described and p38MAPK-dependent actions of IGFBP-5 and the ability of IGFBP-5 to activate p44/p42MAPK (Yasuoka et al, 2009b) have also been reported. It is also still a matter of debate as to whether IGFBPs exert intracellular actions, including within the nucleus.…”

“…Increased IGFBP-5 expression is associated with poor outcome during mammary metastasis (Huynh, 1998, McGuire et al, 1994, Mita et al, 2007, Pekonen et al, 1992. IGFBP-5 also stimulates lung, dermal and hepatic fibroblasts, inducing fibrotic responses similar to those of TGFb1 (Pilewski et al, 2005, Yasuoka et al, 2009a, Yasuoka et al, 2006a, Yasuoka et al, 2009b, Yasuoka et al, 2006b). This was somewhat surprising given that, at high concentrations, IGFBP-5 is apoptotic in mammary epithelial cells in vitro and in vivo (Marshman et al, 2003, Tonner et al, 2002 and is the IGFBP which increases dramatically during involution of the mammary gland (Clarkson andWatson, 2003, Stein et al, 2004) Consistent with an apoptotic function, two recent studies have shown that decreased expression of IGFBP-5 is associated with increased tumourigenesis in osteosarcoma (Su et al, 2011) and in breast cancer induced by foetal alcohol exposure (Polanco et al, 2010).…”