We previously identified the insulin-like growth factor-binding protein 3 (IGFBP-3) as an invasion-suppressor in ovarian endometrioid adenocarcinoma using an ovarian cancer invasion model of OVTW59 sublines and cDNA microarray analysis. IGFBP-3 was found highly expressed in the lower invasive subline P0 and lower expressed in the higher invasive subline P4. The functional role of differential expression of IGFBP-3 in the tumor progression, especially in the invasion and metastasis of ovarian cancer, was studied by IGFBP-3 cDNA transfection into the P4 cells and siRNA transfection into the P0 cells. It was found that higher IGFBP-3 expression was associated with more contracted morphology and lesser cell lamellipodial protrusion. IGFBP-3 could inhibit cell migration in the scratch analysis and cell invasion in the invasion chamber assay; in addition, it could also inhibit tumor growth and metastasis and cause apoptosis in the animal model. IGFBP-3 suppression using siRNA could reverse these functions. We further studied the inhibitory mechanism of IGFBP-3 in cancer migration, invasion and metastasis, especially focusing in the signaling pathways and the interacting genes related to IGFBP-3. Our result showed that IGFBP-3 expression was associated with lower activation of mitogen-activated protein kinases (MAPKs) ERK1 and 2, but not the phosphatidylinositol 3-kinases (PI3K). Inhibition of ERK activity using PD98059 showed similar inhibition of cell migration in scratch test and in three-dimensional culture system. Clinically, 35 patients with ovarian Endometrioid adenocarcinoma were immunostained with IGFBP-3, and low IGFBP-3 expression was found correlated significantly with higher tumor grade, advanced stage and poor survival. Both in animal model and clinical cases, low IGFBP-3 expression was associated significantly with nuclear localization of pERK. It is concluded that the IGFBP-3 gene plays a role as a tumor suppressor in ovarian cancer pathogenesis to inhibit tumor cell migration, invasion and metastasis. The suppression of invasive ability was associated with the inhibition of ERK MAPK signaling pathway.
