Insulin-like growth factor-binding protein-7 functions as a potential tumor suppressor in hepatocellular carcinoma

Abstract

Purpose: Hepatocellular carcinoma (HCC) is a highly virulent malignancy with no effective treatment, thus requiring innovative and effective targeted therapies. The oncogene astrocyte-elevated gene-1 (AEG-1) plays a seminal role in hepatocarcinogenesis and profoundly downregulates insulin-like growth factor-binding protein-7 (IGFBP7). The present study focuses on analyzing potential tumor suppressor functions of IGFBP7 in HCC and the relevance of IGFBP7 downregulation in mediating AEG-1 function.

Experimental design: IGFBP7 expression was detected by immunohistochemistry in HCC tissue microarray and real-time PCR and ELISA in human HCC cell lines. Dual FISH was done to detect LOH at IGFBP7 locus. Stable IGFBP7-overexpressing clones were established in the background of AEG-1-overexpressing human HCC cells and were analyzed for in vitro proliferation and senescence and in vivo tumorigenesis and angiogenesis.

Results: IGFBP7 expression is significantly downregulated in human HCC samples and cell lines compared with normal liver and hepatocytes, respectively, and inversely correlates with the stages and grades of HCC. Genomic deletion of IGFBP7 was identified in 26% of patients with HCC. Forced overexpression of IGFBP7 in AEG-1-overexpressing HCC cells inhibited in vitro growth and induced senescence, and profoundly suppressed in vivo growth in nude mice that might be an end result of inhibition of angiogenesis by IGFBP7.

Conclusion: The present findings provide evidence that IGFBP7 functions as a novel putative tumor suppressor for HCC and establish the corollary that IGFBP7 downregulation can effectively modify AEG-1 function. Accordingly, targeted overexpression of IGFBP7 might be a potential novel therapy for HCC.

Fig. 1

IGFBP7 is downregulated in human HCC samples. A. Analysis of IGFBP7 expression in tissue microarray by immunohistochemistry. C. Fluorescence In Situ Hybridization (FISH) was performed on human HCC samples for IGFBP7 and CEP4 (probe targeting pericentromeric region of chromosome 4). Red: IGFBP7; green: CEP4.

Fig. 2

IGFBP7 is downregulated in human HCC cell lines and by AEG-1. A. Determination of IGFBP7 mRNA expression by real-time PCR in the indicated cells. THLE-3 is normal immortal human hepatocytes. GAPDH was used as normalization control. B. Secreted IGFBP7 protein level in the conditioned media of the indicated cells determined by ELISA. C. Determination of IGFBP7 mRNA expression by real-time PCR in Hep-pc-4 (pc-4) cells and three independent clones of HepG3 cells overexpressing AEG-1. D. Immunofluorescence detection of IGFBP7 protein in Hep-pc-4 (pc-4) and Hep-AEG-1-14 (AEG1-14) cells. E. Immunohistochemical analysis of AEG-1 and IGFBP7 expression in normal liver and matched HCC from the same patient. The figure represents data from one patient. Similar finding was observed in 13 out of 18 HCC patients. For A-C, data represents mean ± SEM of three independent experiments. *: p<0.05.

Fig. 3

Overexpression of IGFBP7 inhibits growth of AEG-1-overexpressing cells. Stable clones of Hep-AEG1-14 cells expressing IGFBP7 (IGFBP7-11 and IGFBP7-12) were generated by selection with zeocin. Zeocin-resistant clone of Hep-AEG1-14 cells (Control-2) served as a control. A. IGFBP7 mRNA expression in the indicated cells detected by real-time PCR. B. Secreted IGFBP7 protein level in the indicated cells detected by ELISA. C. Cell viability (MTT) assay of the indicated cells. D. Colony formation assay of the indicated cells. For A-D, data represents mean ± SEM of three independent experiments. *: p<0.05. E. Western blot analysis performed in the indicated cells with the indicated antibodies. EF1α was used as loading control.

Fig. 4

IGFBP7 induces senescence. A. Photomicrograph of Control-2, IGFBP7-11 and IGFBP7-12 clones of Hep-AEG-1-14 cells stained for senescence-associated β-galactosidase (SA-β-gal) after 1 week of culture. B. Graphical representation of quantification of SA-β-gal positive cells. At least 1,000 cells were counted for each group. Data represents mean ± SEM of three independent experiments. *: p<0.05. C. Photomicrograph of Control-2, IGFBP7-11 and IGFBP7-12 clones of Hep-AEG-1-14 cells stained for γ-H2AX and counterstained with DAPI to stain the nucleus. D. B. Graphical representation of quantification of γ-H2AX foci/cell. At least 100 cells were scored for each group. Data represents mean ± SEM of three independent experiments. *: p<0.05.

Fig. 5

Overexpression of IGFBP7 inhibits AEG-1-mediated tumorigenesis in nude mice. Subcutaneous xenografts were established in athymic nude mice using Control-2, IGFBP7-11 and IGFBP7-12 clones of Hep-AEG-1-14 cells. A. A representative photograph of tumor-bearing mice at the end of the study. B. Measurement of tumor volume at the indicate time point. Data represents mean ± SEM. *: p<0.05. C. Tumor sections were immunostained for IGFBP7, CD31 and Ki-67.

Fig. 6

IGFBP7 inhibits angiogenesis. A. Control-2, IGFBP7-11 and IGFBP7-12 clones of Hep-AEG1-14 cells were implanted in chicken chorioallantoic membrane (CAM) and neovascularization was photographed. B. Graphical representation of new blood vessel formation in CAM when the indicated cells were implanted. The numbers indicate percentage of new blood vessels arising from the existing blood vessels in naïve CAM when VEGF-treated CAM was considered as 100%. Data represents mean ± SEM. *: p<0.05. C. HUVECs were treated with conditioned media from the indicated cells and tube formation was photographed. D. Graphical representation of tube formation by HUVEC treated with conditioned media from the indicated cells. The numbers indicate percentage of tube-like structures when VEGF-treated tube formation was considered as 100%. The data represents mean ± SEM. *: p<0.05.