Down-regulation of hepatoma-derived growth factor inhibits anchorage-independent growth and invasion of non-small cell lung cancer cells

We recently reported that a high level of hepatoma-derived growth factor (HDGF) expression in tumors correlates with a high incidence of tumor relapse or distant metastasis and shortened survival time in patients with non-small cell lung cancer (NSCLC). However, the mechanisms of the HDGF-associated aggressive biological behavior are unknown. In this study, we knocked down HDGF expression in NSCLC cells to determine the biological consequences. Transfection with HDGF-specific small interfering RNA (siRNA) resulted in down-regulation of HDGF expression in four NSCLC cell lines. Down-regulation of HDGF resulted in no detectable effect on anchorage-dependent cell growth as determined with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, a microelectronic cell sensor system, and flow cytometry. In contrast, cells transfected with HDGF-siRNA grew more slowly and formed significantly fewer colonies in soft agar than did cells treated with LipofectAMINE alone or transfected with negative control siRNA. In an in vitro invasion assay, significantly fewer cells transfected with HDGF-siRNA than cells treated with LipofectAMINE alone were able to invade across a Matrigel membrane barrier. In an in vivo mouse model, A549 cells treated with HDGF-siRNA grown significantly slower than the cells treated with LipofectAMINE alone or negative control siRNA. Morphologically, HDGF-siRNA-treated tumors exhibited markedly reduced blood vessel formation and increased necrosis, whereas the Ki67 labeling indices were similar in tumors treated with controls. Our results suggest that HDGF is involved in anchorage-independent growth, cell invasion, and formation of neovasculature of NSCLC. These qualities may contribute to the HDGF-associated aggressive biological behavior of NSCLC.