Inhibition of IGFBP‐5 binding to extracellular matrix and IGF‐I–stimulated DNA synthesis by a peptide fragment of IGFBP‐5

Abstract

Insulin-like growth factor binding protein-5 (IGFBP-5) is synthesized and secreted by smooth muscle cells (SMC). IGFBP-5 synthesis is stimulated five- to sixfold by IGF-I, and IGFBP-5 has been shown to augment IGF-I-stimulated DNA synthesis in this cell type. The ability of IGFBP-5 to augment the SMC response to IGF-I is dependent upon its binding to extracellular matrix. A highly charged region of IGFBP-5 that contains amino acids in positions 201-218 has been shown to mediate binding of IGFBP-5 to human fibroblast extracellular matrix (ECM), and a synthetic peptide containing this sequence inhibits IGFBP-5 binding to fibroblast ECM. In this study we show that exposure of SMC cultures that are constitutively synthesizing IGFBP-5 to a synthetic peptide (termed peptide A) containing this sequence has no effect on its synthesis but reduces its abundance within the ECM. The addition of increasing concentrations of the peptide to SMC cultures resulted in a concentration-dependent reduction in ECM-associated IGFBP-5. In contrast, a control peptide (peptide B), which contained the region of amino acids in positions 131-141 and had a similar charge-to-mass ratio, caused a minimal decrease in ECM binding. This effect was functionally significant since the addition of 10 microg/ml of peptide A inhibited the cellular replication response to 10 ng/ml IGF-I by 51%, and peptide B had no effect. The effects of peptide A were not due to nonspecific cytotoxicity since it had no inhibitory effect on the response of these cells to human serum and was associated with only minimal inhibition of the cellular response to platelet-derived growth factor. The findings suggest that inhibiting IGFBP-5 binding to porcine SMC ECM results in reduced cellular responses to IGF-I.

Regulation of IGFBP‐5 expression during tumourigenesis and differentiation of oral keratinocytes

“…Conversely, the low or absent expression in OSCC counterparts suggests, together with other studies, that the down‐regulation of IGFBP‐5 is an important event in OSCC, as it is in transformed mesenchymal cells and experimental breast cancers 8–12. Since the function of IGFBP‐5 varies in different tissues 6, 12–15, the executive roles of IGFBP‐5 in the proliferation, apoptosis, and migration of OSCC cells, as well as the interaction of IGFBP‐5 with environmental elements that might affect tumour progression, should be carefully addressed 4, 8. We have established that OECM‐1 cells stably express a low level of IGFBP‐5.…”

“…The kinase activity of the putative IGFBP‐5 receptor is enhanced by IGFBP‐5, suggesting that it has a role in mediating IGF‐independent action 7. There is evidence that the IGFBP‐5 gene has a role as a potential suppressor gene through the inhibition of IGF‐I‐induced proliferation and migration of a variety of cells 4, 8–11. It has been shown that inhibition of the growth of MCF‐7 breast adenocarcinoma cells induced by anti‐oestrogen is associated with increased transcription of IGFBP‐5 12.…”

PTEN overexpression suppresses proliferation and differentiation and enhances apoptosis of the mouse mammary epithelium

“…After 48 hours, the medium was removed and fresh medium was added with or without the IGFBP-5-blocking peptide for 24 hours. This IGFBP-5-blocking peptide (25) was kindly provided by D.R. Clemmons (Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA).…”