Insulin-like growth factor binding protein 5 suppresses tumor growth and metastasis of human osteosarcoma

Abstract

Osteosarcoma (OS) is the most common primary malignancy of bone. There is a critical need to identify the events that lead to the poorly understood mechanism of OS development and metastasis. The goal of this investigation is to identify and characterize a novel marker of OS progression. We have established and characterized a highly metastatic OS subline that is derived from the less metastatic human MG63 line through serial passages in nude mice via intratibial injections. Microarray analysis of the parental MG63, the highly metastatic MG63.2 subline, as well as the corresponding primary tumors and pulmonary metastases revealed insulin-like growth factor binding protein 5 (IGFBP5) to be one of the significantly downregulated genes in the metastatic subline. Confirmatory quantitative RT-PCR on 20 genes of interest demonstrated IGFBP5 to be the most differentially expressed and was therefore chosen to be one of the genes for further investigation. Adenoviral mediated overexpression and knockdown of IGFBP5 in the MG63 and MG63.2 cell lines, as well as other OS lines (143B and MNNG/HOS) that are independent of our MG63 lines, were employed to examine the role of IGFBP5. We found that overexpression of IGFBP5 inhibited in vitro cell proliferation, migration and invasion of OS cells. Additionally, IGFBP5 overexpression promoted apoptosis and cell cycle arrest in the G1 phase. In an orthotopic xenograft animal model, overexpression of IGFBP5 inhibited OS tumor growth and pulmonary metastases. Conversely, siRNA-mediated knockdown of IGFBP5 promoted OS tumor growth and pulmonary metastases in vivo. Immunohistochemical staining of patient-matched primary and metastatic OS samples demonstrated decreased IGFBP5 expression in the metastases. These results suggest 1) a role for IGFBP5 as a novel marker that has an important role in the pathogenesis of OS, and 2) that the loss of IGFBP5 function may contribute to more metastatic phenotypes in OS.

c-Src and IL-6 inhibit osteoblast differentiation and integrate IGFBP5 signalling

“…In this instance, the cooperation between c-Src and STAT3 could delay osteoblast differentiation with a positive feedback between IL-6 and c-Src pathways. Consistent with our model, we demonstrated that IL-6 enhances the expression of Igfbp5, which has been described to have important roles in bone physiology and pathology [19][20][21][22] . Interestingly, we found that IGFBP5 directly induced c-Src activation without affecting IGF-1 receptor phosphorylation.…”

Majority of differentially expressed genes are down-regulated during malignant transformation in a four-stage model

“…The involvement of IGFBPs in cancer is not fully understood, but there are reports suggesting that down-regulation of these proteins correlates with cancer progression (28)(29)(30)(31). Fig.…”

IGFBP-5 enhances epithelial cell adhesion and protects epithelial cells from TGFβ1-induced mesenchymal invasion

“…For example, IGFBP-5 expression has recently been shown to be associated with increased survival times in breast cancer patients as well as being responsible for maintaining sensitivity to tamoxifen (Ahn et al , 2010). In addition, overexpression of IGFBP-5 in MCF-7 xenografts inhibited tumour development in mice (Ahn, Elwi, 2010) whilst recent studies have demonstrated a tumour suppressor role for IGFBP-5 in ovarian cancer cells (Rho et al , 2008) in osteosarcoma (Su et al , 2011) and in breast cancer after foetal alcohol exposure (Polanco et al , 2010). An intriguing relationship between IGFBP-5 and tumour dormancy has also been described.…”